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PERLFUNC(1)            Perl Programmers Reference Guide            PERLFUNC(1)

       perlfunc - Perl builtin functions

       The functions in(1,8) this section can serve as terms in(1,8) an expression.
       They fall into two major categories: list operators and named(5,8) unary
       operators.  These differ in(1,8) their precedence relationship with a fol-
       lowing comma.  (See the precedence table in(1,8) perlop.)  List operators
       take more than one argument, while unary operators can never take more
       than one argument.  Thus, a comma terminates the argument of a unary
       operator, but merely separates the arguments of a list operator.  A
       unary operator generally provides a scalar context to its argument,
       while a list operator may provide either scalar or list contexts for
       its arguments.  If it does both, the scalar arguments will be first,
       and the list argument will follow.  (Note that there can ever be only
       one such list argument.)  For instance, splice() has three scalar argu-
       ments followed by a list, whereas gethostbyname() has four scalar argu-

       In the syntax descriptions that follow, list operators that expect a
       list (and provide list context for the elements of the list) are shown
       with LIST as an argument.  Such a list may consist of any combination
       of scalar arguments or list values; the list values will be included in(1,8)
       the list as if(3,n) each individual element were interpolated at that point
       in(1,8) the list, forming a longer single-dimensional list value.  Elements
       of the LIST should be separated by commas.

       Any function in(1,8) the list below may be used either with or without
       parentheses around its arguments.  (The syntax descriptions omit the
       parentheses.)  If you use the parentheses, the simple (but occasionally
       surprising) rule is this: It looks like a function, therefore it is a
       function, and precedence doesn't matter.  Otherwise it's a list opera-
       tor or unary operator, and precedence does matter.  And whitespace
       between the function and left parenthesis doesn't count--so you need to
       be careful sometimes:

           print 1+2+4;        # Prints 7.
           print(1+2) + 4;     # Prints 3.
           print (1+2)+4;      # Also prints 3!
           print +(1+2)+4;     # Prints 7.
           print ((1+2)+4);    # Prints 7.

       If you run Perl with the -w switch(1,n) it can warn you about this.  For
       example, the third line above produces:

           print (...) interpreted as function at - line 1.
           Useless use of integer addition in(1,8) void context at - line 1.

       A few functions take no arguments at all, and therefore work as neither
       unary nor list operators.  These include such functions as "time(1,2,n)" and
       "endpwent".  For example, "time(1,2,n)+86_400" always means "time(1,2,n)() + 86_400".

       For functions that can be used in(1,8) either a scalar or list context, non-
       abortive failure is generally indicated in(1,8) a scalar context by return-
       ing the undefined value, and in(1,8) a list context by returning the null

       Remember the following important rule: There is no rule that relates
       the behavior of an expression in(1,8) list context to its behavior in(1,8) scalar
       context, or vice versa.  It might do two totally different things.
       Each operator and function decides which sort(1,3) of value it would be most
       appropriate to return in(1,8) scalar context.  Some operators return the
       length of the list that would have been returned in(1,8) list context.  Some
       operators return the first value in(1,8) the list.  Some operators return
       the last value in(1,8) the list.  Some operators return a count of success-
       ful operations.  In general, they do what you want, unless you want

       A named(5,8) array in(1,8) scalar context is quite different from what would at
       first glance appear to be a list in(1,8) scalar context.  You can't get a
       list like "(1,2,3)" into being in(1,8) scalar context, because the compiler
       knows the context at compile time.  It would generate the scalar comma
       operator there, not the list construction version(1,3,5) of the comma.  That
       means it was never a list to start with.

       In general, functions in(1,8) Perl that serve as wrappers for system calls
       of the same name (like chown(1,2)(2), fork(2), closedir(2), etc.) all return
       true when they succeed and "undef" otherwise, as is usually mentioned
       in(1,8) the descriptions below.  This is different from the C interfaces,
       which return "-1" on failure.  Exceptions to this rule are "wait",
       "waitpid", and "syscall".  System calls also set(7,n,1 builtins) the special $!  vari-
       able on failure.  Other functions do not, except accidentally.

       Perl Functions by Category

       Here are Perl's functions (including things that look(1,8,3 Search::Dict) like functions,
       like some keywords and named(5,8) operators) arranged by category.  Some
       functions appear in(1,8) more than one place.

       Functions for SCALARs or strings
           "chomp", "chop", "chr", "crypt", "hex", "index", "lc", "lcfirst",
           "length", "oct", "ord", "pack(3,n,n pack-old)", "q/STRING/", "qq/STRING/",
           "reverse", "rindex", "sprintf", "substr", "tr///", "uc", "ucfirst",

       Regular expressions and pattern matching
           "m//", "pos", "quotemeta", "s///", "split(1,n)", "study", "qr//"

       Numeric functions
           "abs", "atan2", "cos", "exp", "hex", "int", "log", "oct", "rand(1,3)",
           "sin", "sqrt", "srand"

       Functions for real @ARRAYs
           "pop", "push", "shift", "splice", "unshift"

       Functions for list data
           "grep", "join(1,n)", "map", "qw/STRING/", "reverse", "sort(1,3)", "unpack"

       Functions for real %HASHes
           "delete", "each", "exists", "keys", "values"

       Input and output functions
           "binmode", "close(2,7,n)", "closedir", "dbmclose", "dbmopen", "die",
           "eof", "fileno", "flock(1,2)", "format", "getc", "print", "printf(1,3,1 builtins)",
           "read(2,n,1 builtins)", "readdir(2,3)", "rewinddir", "seek", "seekdir", "select(2,7,2 select_tut)",
           "syscall", "sysread", "sysseek", "syswrite", "tell", "telldir",
           "truncate(2,7)", "warn", "write(1,2)"

       Functions for fixed length data or records
           "pack(3,n,n pack-old)", "read(2,n,1 builtins)", "syscall", "sysread", "syswrite", "unpack", "vec"

       Functions for filehandles, files, or directories
           "-X", "chdir", "chmod(1,2)", "chown(1,2)", "chroot(1,2)", "fcntl", "glob(1,3,7,n)",
           "ioctl", "link(1,2)", "lstat", "mkdir(1,2)", "open(2,3,n)", "opendir", "readlink(1,2)",
           "rename(1,2,n)", "rmdir(1,2)", "stat(1,2)", "symlink", "sysopen", "umask", "unlink(1,2)",

       Keywords related to the control flow of your perl program
           "caller", "continue", "die", "do", "dump", "eval", "exit(3,n,1 builtins)", "goto",
           "last", "next", "redo", "return", "sub", "wantarray"

       Keywords related to scoping
           "caller", "import", "local", "my", "our", "package", "use"

       Miscellaneous functions
           "defined", "dump", "eval", "formline", "local", "my", "our",
           "reset(1,7,1 tput)", "scalar", "undef", "wantarray"

       Functions for processes and process groups
           "alarm(1,2)", "exec(3,n,1 builtins)", "fork", "getpgrp", "getppid", "getpriority",
           "kill(1,2,1 builtins)", "pipe(2,8)", "qx/STRING/", "setpgrp", "setpriority", "sleep(1,3)",
           "system", "times", "wait", "waitpid"

       Keywords related to perl modules
           "do", "import", "no", "package", "require", "use"

       Keywords related to classes and object-orientedness
           "bless", "dbmclose", "dbmopen", "package", "ref", "tie", "tied",
           "untie", "use"

       Low-level socket(2,7,n) functions
           "accept(2,8)", "bind(2,n,1 builtins)", "connect", "getpeername(1,2)", "getsockname", "get-
           sockopt", "listen(1,2,7)", "recv", "send(2,n)", "setsockopt", "shutdown(2,8)",
           "socket(2,7,n)", "socketpair"

       System V interprocess communication functions
           "msgctl", "msgget", "msgrcv", "msgsnd", "semctl", "semget",
           "semop", "shmctl", "shmget", "shmread", "shmwrite"

       Fetching user and group info(1,5,n)
           "endgrent", "endhostent", "endnetent", "endpwent", "getgrent",
           "getgrgid", "getgrnam", "getlogin", "getpwent", "getpwnam", "getp-
           wuid", "setgrent", "setpwent"

       Fetching network info(1,5,n)
           "endprotoent", "endservent", "gethostbyaddr", "gethostbyname",
           "gethostent", "getnetbyaddr", "getnetbyname", "getnetent", "getpro-
           tobyname", "getprotobynumber", "getprotoent", "getservbyname",
           "getservbyport", "getservent", "sethostent", "setnetent", "setpro-
           toent", "setservent"

       Time-related functions
           "gmtime", "localtime", "time(1,2,n)", "times"

       Functions new in(1,8) perl5
           "abs", "bless", "chomp", "chr", "exists", "formline", "glob(1,3,7,n)",
           "import", "lc", "lcfirst", "map", "my", "no", "our", "prototype",
           "qx", "qw", "readline", "readpipe", "ref", "sub*", "sysopen",
           "tie", "tied", "uc", "ucfirst", "untie", "use"

           * - "sub" was a keyword in(1,8) perl4, but in(1,8) perl5 it is an operator,
           which can be used in(1,8) expressions.

       Functions obsoleted in(1,8) perl5
           "dbmclose", "dbmopen"


       Perl was born in(1,8) Unix and can therefore access(2,5) all common Unix system
       calls.  In non-Unix environments, the functionality of some Unix system
       calls may not be available, or details of the available functionality
       may differ slightly.  The Perl functions affected by this are:

       "-X", "binmode", "chmod(1,2)", "chown(1,2)", "chroot(1,2)", "crypt", "dbmclose",
       "dbmopen", "dump", "endgrent", "endhostent", "endnetent", "endpro-
       toent", "endpwent", "endservent", "exec(3,n,1 builtins)", "fcntl", "flock(1,2)", "fork",
       "getgrent", "getgrgid", "gethostbyname", "gethostent", "getlogin",
       "getnetbyaddr", "getnetbyname", "getnetent", "getppid", "getprgp",
       "getpriority", "getprotobynumber", "getprotoent", "getpwent", "getpw-
       nam", "getpwuid", "getservbyport", "getservent", "getsockopt", "glob(1,3,7,n)",
       "ioctl", "kill(1,2,1 builtins)", "link(1,2)", "lstat", "msgctl", "msgget", "msgrcv",
       "msgsnd", "open(2,3,n)", "pipe(2,8)", "readlink(1,2)", "rename(1,2,n)", "select(2,7,2 select_tut)", "semctl",
       "semget", "semop", "setgrent", "sethostent", "setnetent", "setpgrp",
       "setpriority", "setprotoent", "setpwent", "setservent", "setsockopt",
       "shmctl", "shmget", "shmread", "shmwrite", "socket(2,7,n)", "socketpair",
       "stat(1,2)", "symlink", "syscall", "sysopen", "system", "times", "truncate(2,7)",
       "umask", "unlink(1,2)", "utime", "wait", "waitpid"

       For more information about the portability of these functions, see
       perlport and other available platform-specific documentation.

       Alphabetical Listing of Perl Functions

       -X EXPR
       -X      A file(1,n) test, where X is one of the letters listed below.  This
               unary operator takes one argument, either a filename or a file-
               handle, and tests the associated file(1,n) to see if(3,n) something is
               true about it.  If the argument is omitted, tests $_, except
               for "-t", which tests STDIN.  Unless otherwise documented, it
               returns 1 for true and '' for false, or the undefined value if(3,n)
               the file(1,n) doesn't exist.  Despite the funny names, precedence is
               the same as any other named(5,8) unary operator, and the argument
               may be parenthesized like any other unary operator.  The opera-
               tor may be any of:

                   -r  File is readable by effective uid/gid.
                   -w  File is writable by effective uid/gid.
                   -x  File is executable by effective uid/gid.
                   -o  File is owned by effective uid.

                   -R  File is readable by real uid/gid.
                   -W  File is writable by real uid/gid.
                   -X  File is executable by real uid/gid.
                   -O  File is owned by real uid.

                   -e  File exists.
                   -z  File has zero size (is empty).
                   -s  File has nonzero size (returns size in(1,8) bytes).

                   -f  File is a plain file.
                   -d  File is a directory.
                   -l  File is a symbolic link.
                   -p  File is a named(5,8) pipe(2,8) (FIFO), or Filehandle is a pipe.
                   -S  File is a socket.
                   -b  File is a block special file.
                   -c  File is a character special file.
                   -t  Filehandle is opened to a tty.

                   -u  File has setuid bit set.
                   -g  File has setgid bit set.
                   -k  File has sticky bit set.

                   -T  File is an ASCII text file(1,n) (heuristic guess).
                   -B  File is a "binary" file(1,n) (opposite of -T).

                   -M  Script start time(1,2,n) minus file(1,n) modification time(1,2,n), in(1,8) days.
                   -A  Same for access(2,5) time.
                   -C  Same for inode change time(1,2,n) (Unix, may differ for other platforms)


                   while (<>) {
                       next unless -f $_;      # ignore specials

               The interpretation of the file(1,n) permission operators "-r", "-R",
               "-w", "-W", "-x", and "-X" is by default based solely on the
               mode of the file(1,n) and the uids and gids of the user.  There may
               be other reasons you can't actually read(2,n,1 builtins), write(1,2), or execute the
               file.  Such reasons may be for example network filesystem
               access(2,5) controls, ACLs (access(2,5) control lists), read-only
               filesystems, and unrecognized executable formats.

               Also note that, for the superuser on the local filesystems, the
               "-r", "-R", "-w", and "-W" tests always return 1, and "-x" and
               "-X" return 1 if(3,n) any execute bit is set(7,n,1 builtins) in(1,8) the mode.  Scripts
               run by the superuser may thus need to do a stat(1,2)() to determine
               the actual mode of the file(1,n), or temporarily set(7,n,1 builtins) their effective
               uid to something else.

               If you are using ACLs, there is a pragma called "filetest" that
               may produce more accurate results than the bare stat(1,2)() mode
               bits.  When under the "use filetest 'access(2,5)'" the above-men-
               tioned filetests will test whether the permission can (not) be
               granted using the access(2,5)() family of system calls.  Also note
               that the "-x" and "-X" may under this pragma return true even
               if(3,n) there are no execute permission bits set(7,n,1 builtins) (nor any extra exe-
               cute permission ACLs).  This strangeness is due to the underly-
               ing system calls' definitions.  Read the documentation for the
               "filetest" pragma for more information.

               Note that "-s/a/b/" does not do a negated substitution.  Saying
               "-exp($foo)" still works as expected, however--only single let-
               ters following a minus are interpreted as file(1,n) tests.

               The "-T" and "-B" switches work as follows.  The first block or
               so of the file(1,n) is examined for odd characters such as strange
               control codes or characters with the high bit set.  If too many
               strange characters (>30%) are found, it's a "-B" file(1,n), other-
               wise it's a "-T" file.  Also, any file(1,n) containing null in(1,8) the
               first block is considered a binary file.  If "-T" or "-B" is
               used on a filehandle, the current IO buffer is examined rather
               than the first block.  Both "-T" and "-B" return true on a null
               file(1,n), or a file(1,n) at EOF when testing a filehandle.  Because you
               have to read(2,n,1 builtins) a file(1,n) to do the "-T" test, on most occasions you
               want to use a "-f" against the file(1,n) first, as in(1,8) "next unless
               -f $file(1,n) && -T $file(1,n)".

               If any of the file(1,n) tests (or either the "stat(1,2)" or "lstat" oper-
               ators) are given the special filehandle consisting of a soli-
               tary underline, then the stat(1,2) structure of the previous file(1,n)
               test (or stat(1,2) operator) is used, saving a system call.  (This
               doesn't work with "-t", and you need to remember that lstat()
               and "-l" will leave values in(1,8) the stat(1,2) structure for the sym-
               bolic link(1,2), not the real file.)  (Also, if(3,n) the stat(1,2) buffer was
               filled by a "lstat" call, "-T" and "-B" will reset(1,7,1 tput) it with the
               results of "stat(1,2) _").  Example:

                   print "Can do.\n" if(3,n) -r $a || -w _ || -x _;

                   print "Readable\n" if(3,n) -r _;
                   print "Writable\n" if(3,n) -w _;
                   print "Executable\n" if(3,n) -x _;
                   print "Setuid\n" if(3,n) -u _;
                   print "Setgid\n" if(3,n) -g _;
                   print "Sticky\n" if(3,n) -k _;
                   print "Text\n" if(3,n) -T _;
                   print "Binary\n" if(3,n) -B _;

       abs VALUE
       abs     Returns the absolute value of its argument.  If VALUE is omit-
               ted, uses $_.

               Accepts an incoming socket(2,7,n) connect, just as the accept(2,8)(2) sys-
               tem call does.  Returns the packed address if(3,n) it succeeded,
               false otherwise.  See the example in(1,8) "Sockets: Client/Server
               Communication" in(1,8) perlipc.

               On systems that support a close-on-exec flag on files, the flag
               will be set(7,n,1 builtins) for the newly opened file(1,n) descriptor, as determined
               by the value of $^F.  See "$^F" in(1,8) perlvar.

       alarm(1,2) SECONDS
       alarm(1,2)   Arranges to have a SIGALRM delivered to this process after the
               specified number of wallclock seconds have elapsed.  If SECONDS
               is not specified, the value stored in(1,8) $_ is used. (On some
               machines, unfortunately, the elapsed time(1,2,n) may be up to one sec-
               ond less(1,3) or more than you specified because of how seconds are
               counted, and process scheduling may delay the delivery of the
               signal(2,7) even further.)

               Only one timer may be counting at once.  Each call disables the
               previous timer, and an argument of 0 may be supplied to cancel
               the previous timer without starting a new one.  The returned
               value is the amount of time(1,2,n) remaining on the previous timer.

               For delays of finer granularity than one second, you may use
               Perl's four-argument version(1,3,5) of select(2,7,2 select_tut)() leaving the first
               three arguments undefined, or you might be able to use the
               "syscall" interface to access(2,5) setitimer(2) if(3,n) your system sup-
               ports it.  The Time::HiRes module (from CPAN, and starting from
               Perl 5.8 part of the standard distribution) may also prove use-

               It is usually a mistake to intermix "alarm(1,2)" and "sleep(1,3)" calls.
               ("sleep(1,3)" may be internally implemented in(1,8) your system with

               If you want to use "alarm(1,2)" to time(1,2,n) out a system call you need
               to use an "eval"/"die" pair.  You can't rely on the alarm(1,2) caus-
               ing the system call to fail with $! set(7,n,1 builtins) to "EINTR" because Perl
               sets up signal(2,7) handlers to restart system calls on some sys-
               tems.  Using "eval"/"die" always works, modulo the caveats
               given in(1,8) "Signals" in(1,8) perlipc.

                   eval {
                       local $SIG{ALRM} = sub { die "alarm(1,2)\n" }; # NB: \n required
                       alarm(1,2) $timeout(1,3x,3x cbreak);
                       $nread = sysread SOCKET, $buffer, $size;
                       alarm(1,2) 0;
                   if(3,n) ($@) {
                       die unless $@ eq "alarm(1,2)\n";   # propagate unexpected errors
                       # timed out
                   else {
                       # didn't

               For more information see perlipc.

       atan2 Y,X
               Returns the arctangent of Y/X in(1,8) the range -PI to PI.

               For the tangent operation, you may use the "Math::Trig::tan"
               function, or use the familiar relation:

                   sub tan { sin($_[0]) / cos($_[0])  }

       bind(2,n,1 builtins) SOCKET,NAME
               Binds a network address to a socket(2,7,n), just as the bind(2,n,1 builtins) system
               call does.  Returns true if(3,n) it succeeded, false otherwise.
               NAME should be a packed address of the appropriate type for the
               socket.  See the examples in(1,8) "Sockets: Client/Server Communica-
               tion" in(1,8) perlipc.

       binmode FILEHANDLE, LAYER
       binmode FILEHANDLE
               Arranges for FILEHANDLE to be read(2,n,1 builtins) or written in(1,8) "binary" or
               "text" mode on systems where the run-time libraries distinguish
               between binary and text files.  If FILEHANDLE is an expression,
               the value is taken as the name of the filehandle.  Returns true
               on success, otherwise it returns "undef" and sets $! (errno).

               On some systems (in(1,8) general, DOS and Windows-based systems)
               binmode() is necessary when you're not working with a text
               file.  For the sake of portability it is a good idea to always
               use it when appropriate, and to never use it when it isn't
               appropriate.  Also, people can set(7,n,1 builtins) their I/O to be by default
               UTF-8 encoded Unicode, not bytes.

               In other words: regardless of platform, use binmode() on binary
               data, like for example images.

               If LAYER is present it is a single string(3,n), but may contain mul-
               tiple directives. The directives alter the behaviour of the
               file(1,n) handle.  When LAYER is present using binmode on text file(1,n)
               makes sense.

               If LAYER is omitted or specified as ":raw" the filehandle is
               made suitable for passing binary data. This includes turning
               off possible CRLF translation and marking it as bytes (as
               opposed to Unicode characters).  Note that, despite what may be
               implied in(1,8) "Programming Perl" (the Camel) or elsewhere, ":raw"
               is not the simply inverse of ":crlf" -- other layers which
               would affect binary nature of the stream are also disabled. See
               PerlIO, perlrun and the discussion about the PERLIO environment

               The ":bytes", ":crlf", and ":utf8", and any other directives of
               the form ":...", are called I/O layers.  The "open(2,3,n)" pragma can
               be used to establish default I/O layers.  See open.

               The LAYER parameter of the binmode() function is described as
               "DISCIPLINE" in(1,8) "Programming Perl, 3rd Edition".  However,
               since the publishing of this book, by many known as "Camel
               III", the consensus of the naming of this functionality has
               moved from "discipline" to "layer".  All documentation of this
               version(1,3,5) of Perl therefore refers to "layers" rather than to
               "disciplines".  Now back to the regularly scheduled documenta-

               To mark FILEHANDLE as UTF-8, use ":utf8".

               In general, binmode() should be called after open(2,3,n)() but before
               any I/O is done on the filehandle.  Calling binmode() will nor-
               mally flush(8,n) any pending buffered output data (and perhaps pend-
               ing input data) on the handle.  An exception to this is the
               ":encoding" layer that changes the default character encoding(3,n)
               of the handle, see open.  The ":encoding" layer sometimes needs
               to be called in(1,8) mid-stream, and it doesn't flush(8,n) the stream.
               The ":encoding" also implicitly pushes on top of itself the
               ":utf8" layer because internally Perl will operate on UTF-8
               encoded Unicode characters.

               The operating system, device drivers, C libraries, and Perl
               run-time system all work together to let the programmer treat a
               single character ("\n") as the line terminator, irrespective of
               the external representation.  On many operating systems, the
               native text file(1,n) representation matches the internal represen-
               tation, but on some platforms the external representation of
               "\n" is made up of more than one character.

               Mac OS, all variants of Unix, and Stream_LF files on VMS use a
               single character to end each line in(1,8) the external representa-
               tion of text (even though that single character is CARRIAGE
               RETURN on Mac OS and LINE FEED on Unix and most VMS files). In
               other systems like OS/2, DOS and the various flavors of MS-Win-
               dows your program sees a "\n" as a simple "\cJ", but what's
               stored in(1,8) text files are the two characters "\cM\cJ".  That
               means that, if(3,n) you don't use binmode() on these systems,
               "\cM\cJ" sequences on disk will be converted to "\n" on input,
               and any "\n" in(1,8) your program will be converted back to "\cM\cJ"
               on output.  This is what you want for text files, but it can be
               disastrous for binary files.

               Another consequence of using binmode() (on some systems) is
               that special end-of-file markers will be seen as part of the
               data stream.  For systems from the Microsoft family this means
               that if(3,n) your binary data contains "\cZ", the I/O subsystem will
               regard it as the end of the file(1,n), unless you use binmode().

               binmode() is not only important for readline() and print()
               operations, but also when using read(2,n,1 builtins)(), seek(), sysread(),
               syswrite() and tell() (see perlport for more details).  See the
               $/ and "$\" variables in(1,8) perlvar for how to manually set(7,n,1 builtins) your
               input and output line-termination sequences.

       bless REF,CLASSNAME
       bless REF
               This function tells the thingy referenced by REF that it is now
               an object in(1,8) the CLASSNAME package.  If CLASSNAME is omitted,
               the current package is used.  Because a "bless" is often the
               last thing in(1,8) a constructor, it returns the reference for con-
               venience.  Always use the two-argument version(1,3,5) if(3,n) the function
               doing the blessing might be inherited by a derived class.  See
               perltoot and perlobj for more about the blessing (and bless-
               ings) of objects.

               Consider always blessing objects in(1,8) CLASSNAMEs that are mixed
               case.  Namespaces with all lowercase names are considered
               reserved for Perl pragmata.  Builtin types have all uppercase
               names, so to prevent confusion, you may wish to avoid such
               package names as well.  Make sure that CLASSNAME is a true

               See "Perl Modules" in(1,8) perlmod.

       caller EXPR
       caller  Returns the context of the current subroutine call.  In scalar
               context, returns the caller's package name if(3,n) there is a
               caller, that is, if(3,n) we're in(1,8) a subroutine or "eval" or
               "require", and the undefined value otherwise.  In list context,

                   ($package, $filename, $line) = caller;

               With EXPR, it returns some extra information that the debugger
               uses to print a stack trace.  The value of EXPR indicates how
               many call frames to go back before the current one.

                   ($package, $filename, $line, $subroutine, $hasargs,
                   $wantarray, $evaltext, $is_require, $hints, $bitmask) = caller($i);

               Here $subroutine may be "(eval)" if(3,n) the frame is not a subrou-
               tine call, but an "eval".  In such a case additional elements
               $evaltext and $is_require are set: $is_require is true if(3,n) the
               frame is created by a "require" or "use" statement, $evaltext
               contains the text of the "eval EXPR" statement.  In particular,
               for an "eval BLOCK" statement, $filename is "(eval)", but
               $evaltext is undefined.  (Note also that each "use" statement
               creates a "require" frame inside an "eval EXPR" frame.)  $sub-
               routine may also be "(unknown)" if(3,n) this particular subroutine
               happens to have been deleted from the symbol table.  $hasargs
               is true if(3,n) a new instance of @_ was set(7,n,1 builtins) up for the frame.
               $hints and $bitmask contain pragmatic hints that the caller was
               compiled with.  The $hints and $bitmask values are subject to
               change between versions of Perl, and are not meant for external

               Furthermore, when called from within the DB package, caller
               returns more detailed information: it sets the list variable
               @DB::args to be the arguments with which the subroutine was

               Be aware that the optimizer might have optimized call frames
               away before "caller" had a chance to get the information.  That
               means that caller(N) might not return information about the
               call frame you expect it do, for "N > 1".  In particular,
               @DB::args might have information from the previous time(1,2,n)
               "caller" was called.

       chdir EXPR
               Changes the working directory to EXPR, if(3,n) possible. If EXPR is
               omitted, changes to the directory specified by $ENV{HOME}, if(3,n)
               set(7,n,1 builtins); if(3,n) not, changes to the directory specified by
               $ENV{LOGDIR}. (Under VMS, the variable $ENV{SYS$LOGIN} is also
               checked, and used if(3,n) it is set.) If neither is set(7,n,1 builtins), "chdir"
               does nothing. It returns true upon success, false otherwise.
               See the example under "die".

       chmod(1,2) LIST
               Changes the permissions of a list of files.  The first element
               of the list must be the numerical mode, which should probably
               be an octal number, and which definitely should not a string(3,n) of
               octal digits: 0644 is okay, '0644' is not.  Returns the number
               of files successfully changed.  See also "oct", if(3,n) all you have
               is a string.

                   $cnt = chmod(1,2) 0755, 'foo', 'bar';
                   chmod(1,2) 0755, @executables;
                   $mode = '0644'; chmod(1,2) $mode, 'foo';      # !!! sets mode to
                                                            # --w----r-T
                   $mode = '0644'; chmod(1,2) oct($mode), 'foo'; # this is better
                   $mode = 0644;   chmod(1,2) $mode, 'foo';      # this is best

               You can also import the symbolic "S_I*" constants from the
               Fcntl module:

                   use Fcntl ':mode';

                   chmod(1,2) S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH, @executables;
                   # This is identical to the chmod(1,2) 0755 of the above example.

       chomp VARIABLE
       chomp( LIST )
       chomp   This safer version(1,3,5) of "chop" removes any trailing string(3,n) that
               corresponds to the current value of $/ (also known as
               $INPUT_RECORD_SEPARATOR in(1,8) the "English" module).  It returns
               the total number of characters removed from all its arguments.
               It's often used to remove the newline from the end of an input
               record when you're worried that the final record may be missing
               its newline.  When in(1,8) paragraph mode ("$/ = """), it removes
               all trailing newlines from the string.  When in(1,8) slurp mode ("$/
               = undef") or fixed-length record mode ($/ is a reference to an
               integer or the like, see perlvar) chomp() won't remove any-
               thing.  If VARIABLE is omitted, it chomps $_.  Example:

                   while (<>) {
                       chomp;  # avoid \n on last field
                       @array = split(1,n)(/:/);
                       # ...

               If VARIABLE is a hash, it chomps the hash's values, but not its

               You can actually chomp anything that's an lvalue, including an

                   chomp($cwd = `pwd(1,n,1 builtins)`);
                   chomp($answer = <STDIN>);

               If you chomp a list, each element is chomped, and the total
               number of characters removed is returned.

               If the "encoding(3,n)" pragma is in(1,8) scope then the lengths returned
               are calculated from the length of $/ in(1,8) Unicode characters,
               which is not always the same as the length of $/ in(1,8) the native

               Note that parentheses are necessary when you're chomping any-
               thing that is not a simple variable.  This is because "chomp
               $cwd = `pwd(1,n,1 builtins)`;" is interpreted as "(chomp $cwd) = `pwd(1,n,1 builtins)`;",
               rather than as "chomp( $cwd = `pwd(1,n,1 builtins)` )" which you might expect.
               Similarly, "chomp $a, $b" is interpreted as "chomp($a), $b"
               rather than as "chomp($a, $b)".

       chop VARIABLE
       chop( LIST )
       chop    Chops off the last character of a string(3,n) and returns the char-
               acter chopped.  It is much more efficient than "s/.$//s"
               because it neither scans nor copies the string.  If VARIABLE is
               omitted, chops $_.  If VARIABLE is a hash, it chops the hash's
               values, but not its keys.

               You can actually chop anything that's an lvalue, including an

               If you chop a list, each element is chopped.  Only the value of
               the last "chop" is returned.

               Note that "chop" returns the last character.  To return all but
               the last character, use "substr($string(3,n), 0, -1)".

               See also "chomp".

       chown(1,2) LIST
               Changes the owner (and group) of a list of files.  The first
               two elements of the list must be the numeric uid and gid, in(1,8)
               that order.  A value of -1 in(1,8) either position is interpreted by
               most systems to leave that value unchanged.  Returns the number
               of files successfully changed.

                   $cnt = chown(1,2) $uid, $gid, 'foo', 'bar';
                   chown(1,2) $uid, $gid, @filenames;

               Here's an example that looks up nonnumeric uids in(1,8) the passwd(1,5)

                   print "User: ";
                   chomp($user = <STDIN>);
                   print "Files: ";
                   chomp($pattern = <STDIN>);

                   ($login(1,3,5),$pass,$uid,$gid) = getpwnam($user)
                       or die "$user not in(1,8) passwd(1,5) file(1,n)";

                   @ary = glob(1,3,7,n)($pattern);      # expand filenames
                   chown(1,2) $uid, $gid, @ary;

               On most systems, you are not allowed to change the ownership of
               the file(1,n) unless you're the superuser, although you should be
               able to change the group to any of your secondary groups.  On
               insecure systems, these restrictions may be relaxed, but this
               is not a portable assumption.  On POSIX systems, you can detect
               this condition this way:

                   use POSIX qw(sysconf _PC_CHOWN_RESTRICTED);
                   $can_chown_giveaway = not sysconf(_PC_CHOWN_RESTRICTED);

       chr NUMBER
       chr     Returns the character represented by that NUMBER in(1,8) the charac-
               ter set.  For example, "chr(65)" is "A" in(1,8) either ASCII or Uni-
               code, and chr(0x263a) is a Unicode smiley face.  Note that
               characters from 128 to 255 (inclusive) are by default not
               encoded in(1,8) UTF-8 Unicode for backward compatibility reasons
               (but see encoding(3,n)).

               If NUMBER is omitted, uses $_.

               For the reverse, use "ord".

               Note that under the "bytes" pragma the NUMBER is masked to the
               low eight bits.

               See perlunicode and encoding(3,n) for more about Unicode.

       chroot(1,2) FILENAME
       chroot(1,2)  This function works like the system call by the same name: it
               makes the named(5,8) directory the new root directory for all fur-
               ther pathnames that begin with a "/" by your process and all
               its children.  (It doesn't change your current working direc-
               tory, which is unaffected.)  For security reasons, this call is
               restricted to the superuser.  If FILENAME is omitted, does a
               "chroot(1,2)" to $_.

       close(2,7,n) FILEHANDLE
       close(2,7,n)   Closes the file(1,n) or pipe(2,8) associated with the file(1,n) handle,
               returning true only if(3,n) IO buffers are successfully flushed and
               closes the system file(1,n) descriptor.  Closes the currently
               selected filehandle if(3,n) the argument is omitted.

               You don't have to close(2,7,n) FILEHANDLE if(3,n) you are immediately going
               to do another "open(2,3,n)" on it, because "open(2,3,n)" will close(2,7,n) it for
               you.  (See "open(2,3,n)".)  However, an explicit "close(2,7,n)" on an input
               file(1,n) resets the line counter ($.), while the implicit close(2,7,n)
               done by "open(2,3,n)" does not.

               If the file(1,n) handle came from a piped open(2,3,n), "close(2,7,n)" will addi-
               tionally return false if(3,n) one of the other system calls involved
               fails, or if(3,n) the program exits with non-zero status.  (If the
               only problem was that the program exited non-zero, $! will be
               set(7,n,1 builtins) to 0.)  Closing a pipe(2,8) also waits for the process executing
               on the pipe(2,8) to complete, in(1,8) case you want to look(1,8,3 Search::Dict) at the output
               of the pipe(2,8) afterwards, and implicitly puts(3,n) the exit(3,n,1 builtins) status
               value of that command into $?.

               Prematurely closing the read(2,n,1 builtins) end of a pipe(2,8) (i.e. before the
               process writing to it at the other end has closed it) will
               result in(1,8) a SIGPIPE being delivered to the writer.  If the
               other end can't handle that, be sure to read(2,n,1 builtins) all the data
               before closing the pipe.


                   open(2,3,n)(OUTPUT, '|sort(1,3) >foo')  # pipe(2,8) to sort(1,3)
                       or die "Can't start sort: $!";
                   #...                        # print stuff to output
                   close(2,7,n) OUTPUT                # wait for sort(1,3) to finish
                       or warn $! ? "Error closing sort(1,3) pipe: $!"
                                  : "Exit status $? from sort(1,3)";
                   open(2,3,n)(INPUT, 'foo')          # get sort(1,3)'s results
                       or die "Can't open(2,3,n) 'foo' for input: $!";

               FILEHANDLE may be an expression whose value can be used as an
               indirect filehandle, usually the real filehandle name.

       closedir DIRHANDLE
               Closes a directory opened by "opendir" and returns the success
               of that system call.

       connect SOCKET,NAME
               Attempts to connect to a remote socket(2,7,n), just as the connect
               system call does.  Returns true if(3,n) it succeeded, false other-
               wise.  NAME should be a packed address of the appropriate type
               for the socket.  See the examples in(1,8) "Sockets: Client/Server
               Communication" in(1,8) perlipc.

       continue BLOCK
               Actually a flow control statement rather than a function.  If
               there is a "continue" BLOCK attached to a BLOCK (typically in(1,8) a
               "while" or "foreach"), it is always executed just before the
               conditional is about to be evaluated again, just like the third
               part of a "for" loop in(1,8) C.  Thus it can be used to increment a
               loop variable, even when the loop has been continued via the
               "next" statement (which is similar to the C "continue" state-

               "last", "next", or "redo" may appear within a "continue" block.
               "last" and "redo" will behave as if(3,n) they had been executed
               within the main block.  So will "next", but since it will exe-
               cute a "continue" block, it may be more entertaining.

                   while (EXPR) {
                       ### redo always comes here
                   } continue {
                       ### next always comes here
                       # then back the top to re-check EXPR
                   ### last always comes here

               Omitting the "continue" section is semantically equivalent to
               using an empty one, logically enough.  In that case, "next"
               goes directly back to check the condition at the top of the

       cos EXPR
       cos     Returns the cosine of EXPR (expressed in(1,8) radians).  If EXPR is
               omitted, takes cosine of $_.

               For the inverse cosine operation, you may use the
               "Math::Trig::acos()" function, or use this relation:

                   sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) }

       crypt PLAINTEXT,SALT
               Encrypts a string(3,n) exactly like the crypt(3) function in(1,8) the C
               library (assuming that you actually have a version(1,3,5) there that
               has not been extirpated as a potential munition).  This can
               prove useful for checking the password file(1,n) for lousy pass-
               words, amongst other things.  Only the guys wearing white hats
               should do this.

               Note that crypt is intended to be a one-way function, much like
               breaking eggs to make an omelette.  There is no (known) corre-
               sponding decrypt function (in(1,8) other words, the crypt() is a
               one-way hash function).  As a result, this function isn't all
               that useful for cryptography.  (For that, see your nearby CPAN

               When verifying an existing encrypted string(3,n) you should use the
               encrypted text as the salt (like "crypt($plain, $crypted) eq
               $crypted").  This allows your code to work with the standard
               crypt and with more exotic implementations.  In other words, do
               not assume anything about the returned string(3,n) itself, or how
               many bytes in(1,8) the encrypted string(3,n) matter.

               Traditionally the result is a string(3,n) of 13 bytes: two first
               bytes of the salt, followed by 11 bytes from the set(7,n,1 builtins)
               "[./0-9A-Za-z]", and only the first eight bytes of the
               encrypted string(3,n) mattered, but alternative hashing schemes
               (like MD5), higher level security schemes (like C2), and imple-
               mentations on non-UNIX platforms may produce different strings.

               When choosing a new salt create a random(3,4,6) two character string(3,n)
               whose characters come from the set(7,n,1 builtins) "[./0-9A-Za-z]" (like "join(1,n)
               '', ('.', '/', 0..9, 'A'..'Z', 'a'..'z')[rand(1,3) 64, rand(1,3) 64]").
               This set(7,n,1 builtins) of characters is just a recommendation; the characters
               allowed in(1,8) the salt depend solely on your system's crypt
               library, and Perl can't restrict what salts "crypt()" accepts.

               Here's an example that makes sure that whoever runs this pro-
               gram knows their own password:

                   $pwd(1,n,1 builtins) = (getpwuid($<))[1];

                   system "stty -echo";
                   print "Password: ";
                   chomp($word = <STDIN>);
                   print "\n";
                   system "stty echo(1,3x,1 builtins)";

                   if(3,n) (crypt($word, $pwd(1,n,1 builtins)) ne $pwd(1,n,1 builtins)) {
                       die "Sorry...\n";
                   } else {
                       print "ok\n";

               Of course, typing in(1,8) your own password to whoever asks you for
               it is unwise.

               The crypt function is unsuitable for encrypting large quanti-
               ties of data, not least of all because you can't get the infor-
               mation back.  Look at the by-module/Crypt and by-module/PGP
               directories on your favorite CPAN mirror for a slew of poten-
               tially useful modules.

               If using crypt() on a Unicode string(3,n) (which potentially has
               characters with codepoints above 255), Perl tries to make sense
               of the situation by trying to downgrade (a copy of the string(3,n))
               the string(3,n) back to an eight-bit byte string(3,n) before calling
               crypt() (on that copy).  If that works, good.  If not, crypt()
               dies with "Wide character in(1,8) crypt".

       dbmclose HASH
               [This function has been largely superseded by the "untie" func-

               Breaks the binding between a DBM file(1,n) and a hash.

       dbmopen HASH,DBNAME,MASK
               [This function has been largely superseded by the "tie" func-

               This binds a dbm(3), ndbm(3), sdbm(3), gdbm(3), or Berkeley DB
               file(1,n) to a hash.  HASH is the name of the hash.  (Unlike normal
               "open(2,3,n)", the first argument is not a filehandle, even though it
               looks like one).  DBNAME is the name of the database (without
               the .dir or .pag extension if(3,n) any).  If the database does not
               exist, it is created with protection specified by MASK (as mod-
               ified by the "umask").  If your system supports only the older
               DBM functions, you may perform only one "dbmopen" in(1,8) your pro-
               gram.  In older versions of Perl, if(3,n) your system had neither
               DBM nor ndbm, calling "dbmopen" produced a fatal error(8,n); it now
               falls back to sdbm(3).

               If you don't have write(1,2) access(2,5) to the DBM file(1,n), you can only
               read(2,n,1 builtins) hash variables, not set(7,n,1 builtins) them.  If you want to test whether
               you can write(1,2), either use file(1,n) tests or try setting a dummy
               hash entry inside an "eval", which will trap the error.

               Note that functions such as "keys" and "values" may return huge
               lists when used on large DBM files.  You may prefer to use the
               "each" function to iterate over large DBM files.  Example:

                   # print out history(1,3,n,1 builtins) file(1,n) offsets
                   dbmopen(%HIST,'/usr/lib/news/history(1,3,n,1 builtins)',0666);
                   while (($key,$val) = each %HIST) {
                       print $key, ' = ', unpack('L',$val), "\n";

               See also AnyDBM_File for a more general description of the pros
               and cons of the various dbm approaches, as well as DB_File for
               a particularly rich implementation.

               You can control which DBM library you use by loading that
               library before you call dbmopen():

                   use DB_File;
                   dbmopen(%NS_Hist, "$ENV{HOME}/.netscape/history.db")
                       or die "Can't open(2,3,n) netscape history(1,3,n,1 builtins) file: $!";

       defined EXPR
       defined Returns a Boolean value telling whether EXPR has a value other
               than the undefined value "undef".  If EXPR is not present, $_
               will be checked.

               Many operations return "undef" to indicate failure, end of
               file(1,n), system error(8,n), uninitialized variable, and other excep-
               tional conditions.  This function allows you to distinguish
               "undef" from other values.  (A simple Boolean test will not
               distinguish among "undef", zero, the empty string(3,n), and "0",
               which are all equally false.)  Note that since "undef" is a
               valid scalar, its presence doesn't necessarily indicate an
               exceptional condition: "pop" returns "undef" when its argument
               is an empty array, or when the element to return happens to be

               You may also use "defined(&func)" to check whether subroutine
               &func has ever been defined.  The return value is unaffected by
               any forward declarations of &func.  Note that a subroutine
               which is not defined may still be callable: its package may
               have an "AUTOLOAD" method that makes it spring into existence
               the first time(1,2,n) that it is called -- see perlsub.

               Use of "defined" on aggregates (hashes and arrays) is depre-
               cated.  It used to report whether memory for that aggregate has
               ever been allocated.  This behavior may disappear in(1,8) future
               versions of Perl.  You should instead use a simple test for

                   if(3,n) (@an_array) { print "has array elements\n" }
                   if(3,n) (%a_hash)   { print "has hash members\n"   }

               When used on a hash element, it tells you whether the value is
               defined, not whether the key exists in(1,8) the hash.  Use "exists"
               for the latter purpose.


                   print if(3,n) defined $switch(1,n){'D'};
                   print "$val\n" while defined($val = pop(@ary));
                   die "Can't readlink(1,2) $sym: $!"
                       unless defined($value = readlink(1,2) $sym);
                   sub foo { defined &$bar ? &$bar(@_) : die "No bar"; }
                   $debugging = 0 unless defined $debugging;

               Note:  Many folks tend to overuse "defined", and then are sur-
               prised to discover(1,3,5) that the number 0 and "" (the zero-length
               string(3,n)) are, in(1,8) fact, defined values.  For example, if(3,n) you say

                   "ab" =~ /a(.*)b/;

               The pattern match succeeds, and $1 is defined, despite the fact
               that it matched "nothing".  But it didn't really match noth-
               ing--rather, it matched something that happened to be zero
               characters long.  This is all very above-board and honest.
               When a function returns an undefined value, it's an admission
               that it couldn't give you an honest answer.  So you should use
               "defined" only when you're questioning the integrity of what
               you're trying to do.  At other times, a simple comparison to 0
               or "" is what you want.

               See also "undef", "exists", "ref".

       delete EXPR
               Given an expression that specifies a hash element, array ele-
               ment, hash slice, or array slice, deletes the specified ele-
               ment(s) from the hash or array.  In the case of an array, if(3,n)
               the array elements happen to be at the end, the size of the
               array will shrink to the highest element that tests true for
               exists() (or 0 if(3,n) no such element exists).

               Returns a list with the same number of elements as the number
               of elements for which deletion was attempted.  Each element of
               that list consists of either the value of the element deleted,
               or the undefined value.  In scalar context, this means that you
               get the value of the last element deleted (or the undefined
               value if(3,n) that element did not exist).

                   %hash = (foo => 11, bar => 22, baz => 33);
                   $scalar = delete $hash{foo};             # $scalar is 11
                   $scalar = delete @hash{qw(foo bar)};     # $scalar is 22
                   @array  = delete @hash{qw(foo bar baz)}; # @array  is (undef,undef,33)

               Deleting from %ENV modifies the environment.  Deleting from a
               hash tied to a DBM file(1,n) deletes the entry from the DBM file.
               Deleting from a "tie"d hash or array may not necessarily return

               Deleting an array element effectively returns that position of
               the array to its initial, uninitialized state.  Subsequently
               testing for the same element with exists() will return false.
               Note that deleting array elements in(1,8) the middle of an array
               will not shift the index of the ones after them down--use
               splice() for that.  See "exists".

               The following (inefficiently) deletes all the values of %HASH
               and @ARRAY:

                   foreach $key (keys %HASH) {
                       delete $HASH{$key};

                   foreach $index (0 .. $#ARRAY) {
                       delete $ARRAY[$index];

               And so do these:

                   delete @HASH{keys %HASH};

                   delete @ARRAY[0 .. $#ARRAY];

               But both of these are slower than just assigning the empty list
               or undefining %HASH or @ARRAY:

                   %HASH = ();         # completely empty %HASH
                   undef %HASH;        # forget %HASH ever existed

                   @ARRAY = ();        # completely empty @ARRAY
                   undef @ARRAY;       # forget @ARRAY ever existed

               Note that the EXPR can be arbitrarily complicated as long as
               the final operation is a hash element, array element,  hash
               slice, or array slice lookup:

                   delete $ref->[$x][$y]{$key};
                   delete @{$ref->[$x][$y]}{$key1, $key2, @morekeys};

                   delete $ref->[$x][$y][$index];
                   delete @{$ref->[$x][$y]}[$index1, $index2, @moreindices];

       die LIST
               Outside an "eval", prints the value of LIST to "STDERR" and
               exits with the current value of $! (errno).  If $! is 0, exits
               with the value of "($? >> 8)" (backtick `command` status).  If
               "($? >> 8)" is 0, exits with 255.  Inside an "eval()," the
               error(8,n) message is stuffed into $@ and the "eval" is terminated
               with the undefined value.  This makes "die" the way to raise(3,n) an

               Equivalent examples:

                   die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news';
                   chdir '/usr/spool/news' or die "Can't cd to spool: $!\n"

               If the last element of LIST does not end in(1,8) a newline, the cur-
               rent script line number and input line number (if(3,n) any) are also
               printed, and a newline is supplied.  Note that the "input line
               number" (also known as "chunk") is subject to whatever notion
               of "line" happens to be currently in(1,8) effect, and is also avail-
               able as the special variable $..  See "$/" in(1,8) perlvar and "$."
               in(1,8) perlvar.

               Hint: sometimes appending ", stopped" to your message will
               cause it to make better sense when the string(3,n) "at foo line 123"
               is appended.  Suppose you are running script "canasta".

                   die "/etc/games is no good";
                   die "/etc/games is no good, stopped";

               produce, respectively

                   /etc/games is no good at canasta line 123.
                   /etc/games is no good, stopped at canasta line 123.

               See also exit(3,n,1 builtins)(), warn(), and the Carp module.

               If LIST is empty and $@ already contains a value (typically
               from a previous eval) that value is reused after appending
               "\t...propagated".  This is useful for propagating exceptions:

                   eval { ... };
                   die unless $@ =~ /Expected exception/;

               If LIST is empty and $@ contains an object reference that has a
               "PROPAGATE" method, that method will be called with additional
               file(1,n) and line number parameters.  The return value replaces the
               value in(1,8) $@.  ie. as if(3,n) "$@ = eval { $@->PROPAGATE(__FILE__,
               __LINE__) };" were called.

               If $@ is empty then the string(3,n) "Died" is used.

               die() can also be called with a reference argument.  If this
               happens to be trapped within an eval(), $@ contains the refer-
               ence.  This behavior permits a more elaborate exception han-
               dling implementation using objects that maintain arbitrary
               state about the nature of the exception.  Such a scheme is
               sometimes preferable to matching particular string(3,n) values of $@
               using regular expressions.  Here's an example:

                   eval { ... ; die Some::Module::Exception->new( FOO => "bar" ) };
                   if(3,n) ($@) {
                       if(3,n) (ref($@) && UNIVERSAL::isa($@,"Some::Module::Exception")) {
                           # handle Some::Module::Exception
                       else {
                           # handle all other possible exceptions

               Because perl will stringify uncaught exception messages before
               displaying them, you may want to overload stringification oper-
               ations on such custom exception objects.  See overload for
               details about that.

               You can arrange for a callback to be run just before the "die"
               does its deed, by setting the $SIG{__DIE__} hook.  The associ-
               ated handler will be called with the error(8,n) text and can change
               the error(8,n) message, if(3,n) it sees fit, by calling "die" again.  See
               "$SIG{expr(1,3,n)}" in(1,8) perlvar for details on setting %SIG entries,
               and "eval BLOCK" for some examples.  Although this feature was
               meant to be run only right before your program was to exit(3,n,1 builtins),
               this is not currently the case--the $SIG{__DIE__} hook is cur-
               rently called even inside eval()ed blocks/strings!  If one
               wants the hook to do nothing in(1,8) such situations, put

                       die @_ if(3,n) $^S;

               as the first line of the handler (see "$^S" in(1,8) perlvar).
               Because this promotes strange action at a distance, this coun-
               terintuitive behavior may be fixed in(1,8) a future release.

       do BLOCK
               Not really a function.  Returns the value of the last command
               in(1,8) the sequence of commands indicated by BLOCK.  When modified
               by a loop modifier, executes the BLOCK once before testing the
               loop condition.  (On other statements the loop modifiers test
               the conditional first.)

               "do BLOCK" does not count as a loop, so the loop control state-
               ments "next", "last", or "redo" cannot be used to leave or
               restart the block.  See perlsyn for alternative strategies.

               A deprecated form of subroutine call.  See perlsub.

       do EXPR Uses the value of EXPR as a filename and executes the contents
               of the file(1,n) as a Perl script.  Its primary use is to include
               subroutines from a Perl subroutine library.

                   do '';

               is just like

                   eval `cat`;

               except that it's more efficient and concise, keeps track of the
               current filename for error(8,n) messages, searches the @INC
               libraries, and updates %INC if(3,n) the file(1,n) is found.  See "Prede-
               fined Names" in(1,8) perlvar for these variables.  It also differs
               in(1,8) that code evaluated with "do FILENAME" cannot see lexicals
               in(1,8) the enclosing scope; "eval STRING" does.  It's the same,
               however, in(1,8) that it does reparse the file(1,n) every time(1,2,n) you call
               it, so you probably don't want to do this inside a loop.

               If "do" cannot read(2,n,1 builtins) the file(1,n), it returns undef and sets $! to
               the error.  If "do" can read(2,n,1 builtins) the file(1,n) but cannot compile it, it
               returns undef and sets an error(8,n) message in(1,8) $@.   If the file(1,n) is
               successfully compiled, "do" returns the value of the last
               expression evaluated.

               Note that inclusion of library modules is better done with the
               "use" and "require" operators, which also do automatic error(8,n)
               checking and raise(3,n) an exception if(3,n) there's a problem.

               You might like to use "do" to read(2,n,1 builtins) in(1,8) a program configuration
               file.  Manual error(8,n) checking can be done this way:

                   # read(2,n,1 builtins) in(1,8) config(1,5) files: system first, then user
                   for $file(1,n) ("/share/prog/defaults.rc",
                       unless ($return = do $file(1,n)) {
                           warn "couldn't parse $file: $@" if(3,n) $@;
                           warn "couldn't do $file: $!"    unless defined $return;
                           warn "couldn't run $file(1,n)"       unless $return;

       dump LABEL
       dump    This function causes an immediate core dump.  See also the -u
               command-line switch(1,n) in(1,8) perlrun, which does the same thing.
               Primarily this is so that you can use the undump program (not
               supplied) to turn your core dump into an executable binary
               after having initialized all your variables at the beginning of
               the program.  When the new binary is executed it will begin by
               executing a "goto LABEL" (with all the restrictions that "goto"
               suffers).  Think of it as a goto with an intervening core dump
               and reincarnation.  If "LABEL" is omitted, restarts the program
               from the top.

               WARNING: Any files opened at the time(1,2,n) of the dump will not be
               open(2,3,n) any more when the program is reincarnated, with possible
               resulting confusion on the part of Perl.

               This function is now largely obsolete, partly because it's very
               hard to convert a core file(1,n) into an executable, and because the
               real compiler backends for generating portable bytecode and
               compilable C code have superseded it.  That's why you should
               now invoke it as "CORE::dump()", if(3,n) you don't want to be warned
               against a possible typo.

               If you're looking to use dump to speed up your program, con-
               sider generating bytecode or native C code as described in(1,8)
               perlcc.  If you're just trying to accelerate a CGI script, con-
               sider using the "mod_perl" extension to Apache, or the CPAN
               module, CGI::Fast.  You might also consider autoloading or
               selfloading, which at least make your program appear to run

       each HASH
               When called in(1,8) list context, returns a 2-element list consist-
               ing of the key and value for the next element of a hash, so
               that you can iterate over it.  When called in(1,8) scalar context,
               returns only the key for the next element in(1,8) the hash.

               Entries are returned in(1,8) an apparently random(3,4,6) order.  The actual
               random(3,4,6) order is subject to change in(1,8) future versions of perl,
               but it is guaranteed to be in(1,8) the same order as either the
               "keys" or "values" function would produce on the same (unmodi-
               fied) hash.  Since Perl 5.8.1 the ordering is different even
               between different runs of Perl for security reasons (see "Algo-
               rithmic Complexity Attacks" in(1,8) perlsec).

               When the hash is entirely read(2,n,1 builtins), a null array is returned in(1,8)
               list context (which when assigned produces a false (0) value),
               and "undef" in(1,8) scalar context.  The next call to "each" after
               that will start iterating again.  There is a single iterator
               for each hash, shared by all "each", "keys", and "values" func-
               tion calls in(1,8) the program; it can be reset(1,7,1 tput) by reading all the
               elements from the hash, or by evaluating "keys HASH" or "values
               HASH".  If you add or delete elements of a hash while you're
               iterating over it, you may get entries skipped or duplicated,
               so don't.  Exception: It is always safe to delete the item most
               recently returned by "each()", which means that the following
               code will work:

                       while (($key, $value) = each %hash) {
                         print $key, "\n";
                         delete $hash{$key};   # This is safe

               The following prints out your environment like the printenv(1)
               program, only in(1,8) a different order:

                   while (($key,$value) = each %ENV) {
                       print "$key=$value\n";

               See also "keys", "values" and "sort(1,3)".

       eof FILEHANDLE
       eof ()
       eof     Returns 1 if(3,n) the next read(2,n,1 builtins) on FILEHANDLE will return end of
               file(1,n), or if(3,n) FILEHANDLE is not open.  FILEHANDLE may be an
               expression whose value gives the real filehandle.  (Note that
               this function actually reads a character and then "ungetc"s it,
               so isn't very useful in(1,8) an interactive context.)  Do not read(2,n,1 builtins)
               from a terminal file(1,n) (or call "eof(FILEHANDLE)" on it) after
               end-of-file is reached.  File types such as terminals may lose
               the end-of-file condition if(3,n) you do.

               An "eof" without an argument uses the last file(1,n) read.  Using
               "eof()" with empty parentheses is very different.  It refers to
               the pseudo file(1,n) formed from the files listed on the command
               line and accessed via the "<>" operator.  Since "<>" isn't
               explicitly opened, as a normal filehandle is, an "eof()" before
               "<>" has been used will cause @ARGV to be examined to determine
               if(3,n) input is available.   Similarly, an "eof()" after "<>" has
               returned end-of-file will assume you are processing another
               @ARGV list, and if(3,n) you haven't set(7,n,1 builtins) @ARGV, will read(2,n,1 builtins) input from
               "STDIN"; see "I/O Operators" in(1,8) perlop.

               In a "while (<>)" loop, "eof" or "eof(ARGV)" can be used to
               detect the end of each file(1,n), "eof()" will only detect the end
               of the last file.  Examples:

                   # reset(1,7,1 tput) line numbering on each input file(1,n)
                   while (<>) {
                       next if(3,n) /^\s*#/;        # skip comments
                       print "$.\t$_";
                   } continue {
                       close(2,7,n) ARGV  if(3,n) eof;     # Not eof()!

                   # insert dashes just before last line of last file(1,n)
                   while (<>) {
                       if(3,n) (eof()) {            # check for end of last file(1,n)
                           print "--------------\n";
                       last if(3,n) eof();          # needed if(3,n) we're reading from a terminal

               Practical hint: you almost never need to use "eof" in(1,8) Perl,
               because the input operators typically return "undef" when they
               run out of data, or if(3,n) there was an error.

       eval EXPR
       eval BLOCK
               In the first form, the return value of EXPR is parsed and exe-
               cuted as if(3,n) it were a little Perl program.  The value of the
               expression (which is itself determined within scalar context)
               is first parsed, and if(3,n) there weren't any errors, executed in(1,8)
               the lexical context of the current Perl program, so that any
               variable settings or subroutine and format definitions remain
               afterwards.  Note that the value is parsed every time(1,2,n) the eval
               executes.  If EXPR is omitted, evaluates $_.  This form is typ-
               ically used to delay parsing and subsequent execution of the
               text of EXPR until run time.

               In the second form, the code within the BLOCK is parsed only
               once--at the same time(1,2,n) the code surrounding the eval itself was
               parsed--and executed within the context of the current Perl
               program.  This form is typically used to trap exceptions more
               efficiently than the first (see below), while also providing
               the benefit of checking the code within BLOCK at compile time.

               The final semicolon, if(3,n) any, may be omitted from the value of
               EXPR or within the BLOCK.

               In both forms, the value returned is the value of the last
               expression evaluated inside the mini-program; a return state-
               ment may be also used, just as with subroutines.  The expres-
               sion providing the return value is evaluated in(1,8) void, scalar,
               or list context, depending on the context of the eval itself.
               See "wantarray" for more on how the evaluation context can be

               If there is a syntax error(8,n) or runtime error(8,n), or a "die" state-
               ment is executed, an undefined value is returned by "eval", and
               $@ is set(7,n,1 builtins) to the error(8,n) message.  If there was no error(8,n), $@ is
               guaranteed to be a null string.  Beware that using "eval" nei-
               ther silences perl from printing warnings to STDERR, nor does
               it stuff the text of warning messages into $@.  To do either of
               those, you have to use the $SIG{__WARN__} facility, or turn off
               warnings inside the BLOCK or EXPR using "no warnings 'all'".
               See "warn", perlvar, warnings and perllexwarn.

               Note that, because "eval" traps otherwise-fatal errors, it is
               useful for determining whether a particular feature (such as
               "socket(2,7,n)" or "symlink") is implemented.  It is also Perl's
               exception trapping mechanism, where the die operator is used to
               raise(3,n) exceptions.

               If the code to be executed doesn't vary, you may use the eval-
               BLOCK form to trap run-time errors without incurring the
               penalty of recompiling each time.  The error(8,n), if(3,n) any, is still
               returned in(1,8) $@.  Examples:

                   # make divide-by-zero nonfatal
                   eval { $answer = $a / $b; }; warn $@ if(3,n) $@;

                   # same thing, but less(1,3) efficient
                   eval '$answer = $a / $b'; warn $@ if(3,n) $@;

                   # a compile-time error(8,n)
                   eval { $answer = };                 # WRONG

                   # a run-time error(8,n)
                   eval '$answer =';   # sets $@

               Due to the current arguably broken state of "__DIE__" hooks,
               when using the "eval{}" form as an exception trap in(1,8) libraries,
               you may wish not to trigger any "__DIE__" hooks that user code
               may have installed.  You can use the "local $SIG{__DIE__}" con-
               struct for this purpose, as shown in(1,8) this example:

                   # a very private exception trap for divide-by-zero
                   eval { local $SIG{'__DIE__'}; $answer = $a / $b; };
                   warn $@ if(3,n) $@;

               This is especially significant, given that "__DIE__" hooks can
               call "die" again, which has the effect of changing their error(8,n)

                   # __DIE__ hooks may modify error(8,n) messages
                      local $SIG{'__DIE__'} =
                             sub { (my $x = $_[0]) =~ s/foo/bar/g; die $x };
                      eval { die "foo lives here" };
                      print $@ if(3,n) $@;                # prints "bar lives here"

               Because this promotes action at a distance, this counterintu-
               itive behavior may be fixed in(1,8) a future release.

               With an "eval", you should be especially careful to remember
               what's being looked at when:

                   eval $x;            # CASE 1
                   eval "$x";          # CASE 2

                   eval '$x';          # CASE 3
                   eval { $x };        # CASE 4

                   eval "\$$x++";      # CASE 5
                   $$x++;              # CASE 6

               Cases 1 and 2 above behave identically: they run the code con-
               tained in(1,8) the variable $x.  (Although case 2 has misleading
               double quotes making the reader wonder what else might be hap-
               pening (nothing is).)  Cases 3 and 4 likewise behave in(1,8) the
               same way: they run the code '$x', which does nothing but return
               the value of $x.  (Case 4 is preferred for purely visual rea-
               sons, but it also has the advantage of compiling at compile-
               time(1,2,n) instead of at run-time.)  Case 5 is a place where normally
               you would like to use double quotes, except that in(1,8) this par-
               ticular situation, you can just use symbolic references
               instead, as in(1,8) case 6.

               "eval BLOCK" does not count as a loop, so the loop control
               statements "next", "last", or "redo" cannot be used to leave or
               restart the block.

               Note that as a very special case, an "eval ''" executed within
               the "DB" package doesn't see the usual surrounding lexical
               scope, but rather the scope of the first non-DB piece of code
               that called it. You don't normally need to worry about this
               unless you are writing a Perl debugger.

       exec(3,n,1 builtins) LIST
       exec(3,n,1 builtins) PROGRAM LIST
               The "exec(3,n,1 builtins)" function executes a system command and never
               returns-- use "system" instead of "exec(3,n,1 builtins)" if(3,n) you want it to
               return.  It fails and returns false only if(3,n) the command does
               not exist and it is executed directly instead of via your sys-
               tem's command shell (see below).

               Since it's a common mistake to use "exec(3,n,1 builtins)" instead of "system",
               Perl warns you if(3,n) there is a following statement which isn't
               "die", "warn", or "exit(3,n,1 builtins)" (if(3,n) "-w" is set(7,n,1 builtins)  -  but you always do
               that).   If you really want to follow an "exec(3,n,1 builtins)" with some other
               statement, you can use one of these styles to avoid the warn-

                   exec(3,n,1 builtins) ('foo')   or print STDERR "couldn't exec(3,n,1 builtins) foo: $!";
                   { exec(3,n,1 builtins) ('foo') }; print STDERR "couldn't exec(3,n,1 builtins) foo: $!";

               If there is more than one argument in(1,8) LIST, or if(3,n) LIST is an
               array with more than one value, calls execvp(3) with the argu-
               ments in(1,8) LIST.  If there is only one scalar argument or an
               array with one element in(1,8) it, the argument is checked for shell
               metacharacters, and if(3,n) there are any, the entire argument is
               passed to the system's command shell for parsing (this is
               "/bin/sh -c" on Unix platforms, but varies on other platforms).
               If there are no shell metacharacters in(1,8) the argument, it is
               split(1,n) into words and passed directly to "execvp", which is more
               efficient.  Examples:

                   exec(3,n,1 builtins) '/bin/echo(1,3x,1 builtins)', 'Your arguments are: ', @ARGV;
                   exec(3,n,1 builtins) "sort(1,3) $outfile | uniq";

               If you don't really want to execute the first argument, but
               want to lie to the program you are executing about its own
               name, you can specify the program you actually want to run as
               an "indirect object" (without a comma) in(1,8) front of the LIST.
               (This always forces interpretation of the LIST as a multivalued
               list, even if(3,n) there is only a single scalar in(1,8) the list.)

                   $shell = '/bin/csh';
                   exec(3,n,1 builtins) $shell '-sh';          # pretend it's a login(1,3,5) shell

               or, more directly,

                   exec(3,n,1 builtins) {'/bin/csh'} '-sh';    # pretend it's a login(1,3,5) shell

               When the arguments get executed via the system shell, results
               will be subject to its quirks and capabilities.  See "`STRING`"
               in(1,8) perlop for details.

               Using an indirect object with "exec(3,n,1 builtins)" or "system" is also more
               secure.  This usage (which also works fine with system())
               forces interpretation of the arguments as a multivalued list,
               even if(3,n) the list had just one argument.  That way you're safe
               from the shell expanding wildcards or splitting up words with
               whitespace in(1,8) them.

                   @args = ( "echo(1,3x,1 builtins) surprise" );

                   exec(3,n,1 builtins) @args;               # subject to shell escapes
                                               # if(3,n) @args == 1
                   exec(3,n,1 builtins) { $args[0] } @args;  # safe even with one-arg list

               The first version(1,3,5), the one without the indirect object, ran the
               echo(1,3x,1 builtins) program, passing it "surprise" an argument.  The second
               version(1,3,5) didn't--it tried to run a program literally called
               "echo(1,3x,1 builtins) surprise", didn't find it, and set(7,n,1 builtins) $? to a non-zero value
               indicating failure.

               Beginning with v5.6.0, Perl will attempt to flush(8,n) all files
               opened for output before the exec(3,n,1 builtins), but this may not be sup-
               ported on some platforms (see perlport).  To be safe, you may
               need to set(7,n,1 builtins) $| ($AUTOFLUSH in(1,8) English) or call the "aut-
               oflush()" method of "IO::Handle" on any open(2,3,n) handles in(1,8) order
               to avoid lost output.

               Note that "exec(3,n,1 builtins)" will not call your "END" blocks, nor will it
               call any "DESTROY" methods in(1,8) your objects.

       exists EXPR
               Given an expression that specifies a hash element or array ele-
               ment, returns true if(3,n) the specified element in(1,8) the hash or
               array has ever been initialized, even if(3,n) the corresponding
               value is undefined.  The element is not autovivified if(3,n) it
               doesn't exist.

                   print "Exists\n"    if(3,n) exists $hash{$key};
                   print "Defined\n"   if(3,n) defined $hash{$key};
                   print "True\n"      if(3,n) $hash{$key};

                   print "Exists\n"    if(3,n) exists $array[$index];
                   print "Defined\n"   if(3,n) defined $array[$index];
                   print "True\n"      if(3,n) $array[$index];

               A hash or array element can be true only if(3,n) it's defined, and
               defined if(3,n) it exists, but the reverse doesn't necessarily hold

               Given an expression that specifies the name of a subroutine,
               returns true if(3,n) the specified subroutine has ever been
               declared, even if(3,n) it is undefined.  Mentioning a subroutine
               name for exists or defined does not count as declaring it.
               Note that a subroutine which does not exist may still be
               callable: its package may have an "AUTOLOAD" method that makes
               it spring into existence the first time(1,2,n) that it is called --
               see perlsub.

                   print "Exists\n"    if(3,n) exists &subroutine;
                   print "Defined\n"   if(3,n) defined &subroutine;

               Note that the EXPR can be arbitrarily complicated as long as
               the final operation is a hash or array key lookup or subroutine

                   if(3,n) (exists $ref->{A}->{B}->{$key})  { }
                   if(3,n) (exists $hash{A}{B}{$key})       { }

                   if(3,n) (exists $ref->{A}->{B}->[$ix])   { }
                   if(3,n) (exists $hash{A}{B}[$ix])        { }

                   if(3,n) (exists &{$ref->{A}{B}{$key}})   { }

               Although the deepest nested array or hash will not spring into
               existence just because its existence was tested, any interven-
               ing ones will.  Thus "$ref->{"A"}" and "$ref->{"A"}->{"B"}"
               will spring into existence due to the existence test for the
               $key element above.  This happens anywhere the arrow operator
               is used, including even:

                   undef $ref;
                   if(3,n) (exists $ref->{"Some key"})      { }
                   print $ref;             # prints HASH(0x80d3d5c)

               This surprising autovivification in(1,8) what does not at first--or
               even second--glance appear to be an lvalue context may be fixed
               in(1,8) a future release.

               See "Pseudo-hashes: Using an array as a hash" in(1,8) perlref for
               specifics on how exists() acts when used on a pseudo-hash.

               Use of a subroutine call, rather than a subroutine name, as an
               argument to exists() is an error.

                   exists &sub;        # OK
                   exists &sub();      # Error

       exit(3,n,1 builtins) EXPR
               Evaluates EXPR and exits immediately with that value.    Exam-

                   $ans = <STDIN>;
                   exit(3,n,1 builtins) 0 if(3,n) $ans =~ /^[Xx]/;

               See also "die".  If EXPR is omitted, exits with 0 status.  The
               only universally recognized values for EXPR are 0 for success
               and 1 for error(8,n); other values are subject to interpretation
               depending on the environment in(1,8) which the Perl program is run-
               ning.  For example, exiting 69 (EX_UNAVAILABLE) from a sendmail(1,8)
               incoming-mail filter(1,3x,3x curs_util) will cause the mailer to return the item
               undelivered, but that's not true everywhere.

               Don't use "exit(3,n,1 builtins)" to abort(3,7) a subroutine if(3,n) there's any chance
               that someone might want to trap whatever error(8,n) happened.  Use
               "die" instead, which can be trapped by an "eval".

               The exit(3,n,1 builtins)() function does not always exit(3,n,1 builtins) immediately.  It calls
               any defined "END" routines first, but these "END" routines may
               not themselves abort(3,7) the exit.  Likewise any object destructors
               that need to be called are called before the real exit.  If
               this is a problem, you can call "POSIX:_exit($status)" to avoid
               END and destructor processing.  See perlmod for details.

       exp EXPR
       exp     Returns e (the natural logarithm base) to the power of EXPR.
               If EXPR is omitted, gives "exp($_)".

               Implements the fcntl(2) function.  You'll probably have to say

                   use Fcntl;

               first to get the correct constant definitions.  Argument pro-
               cessing and value return works just like "ioctl" below.  For

                   use Fcntl;
                   fcntl($filehandle, F_GETFL, $packed_return_buffer)
                       or die "can't fcntl F_GETFL: $!";

               You don't have to check for "defined" on the return from
               "fcntl".  Like "ioctl", it maps a 0 return from the system call
               into "0 but true" in(1,8) Perl.  This string(3,n) is true in(1,8) boolean con-
               text and 0 in(1,8) numeric context.  It is also exempt from the nor-
               mal -w warnings on improper numeric conversions.

               Note that "fcntl" will produce a fatal error(8,n) if(3,n) used on a
               machine that doesn't implement fcntl(2).  See the Fcntl module
               or your fcntl(2) manpage to learn what functions are available
               on your system.

               Here's an example of setting a filehandle named(5,8) "REMOTE" to be
               non-blocking at the system level.  You'll have to negotiate $|
               on your own, though.

                   use Fcntl qw(F_GETFL F_SETFL O_NONBLOCK);

                   $flags = fcntl(REMOTE, F_GETFL, 0)
                               or die "Can't get flags for the socket: $!\n";

                   $flags = fcntl(REMOTE, F_SETFL, $flags | O_NONBLOCK)
                               or die "Can't set(7,n,1 builtins) flags for the socket: $!\n";

       fileno FILEHANDLE
               Returns the file(1,n) descriptor for a filehandle, or undefined if(3,n)
               the filehandle is not open.  This is mainly useful for con-
               structing bitmaps for "select(2,7,2 select_tut)" and low-level POSIX tty-handling
               operations.  If FILEHANDLE is an expression, the value is taken
               as an indirect filehandle, generally its name.

               You can use this to find out whether two handles refer to the
               same underlying descriptor:

                   if(3,n) (fileno(THIS) == fileno(THAT)) {
                       print "THIS and THAT are dups\n";

               (Filehandles connected to memory objects via new features of
               "open(2,3,n)" may return undefined even though they are open.)

       flock(1,2) FILEHANDLE,OPERATION
               Calls flock(1,2)(2), or an emulation of it, on FILEHANDLE.  Returns
               true for success, false on failure.  Produces a fatal error(8,n) if(3,n)
               used on a machine that doesn't implement flock(1,2)(2), fcntl(2)
               locking, or lockf(3).  "flock(1,2)" is Perl's portable file(1,n) locking
               interface, although it locks only entire files, not records.

               Two potentially non-obvious but traditional "flock(1,2)" semantics
               are that it waits indefinitely until the lock is granted, and
               that its locks merely advisory.  Such discretionary locks are
               more flexible, but offer fewer guarantees.  This means that
               files locked with "flock(1,2)" may be modified by programs that do
               not also use "flock(1,2)".  See perlport, your port's specific docu-
               mentation, or your system-specific local manpages for details.
               It's best to assume traditional behavior if(3,n) you're writing por-
               table programs.  (But if(3,n) you're not, you should as always feel
               perfectly free to write(1,2) for your own system's idiosyncrasies
               (sometimes called "features").  Slavish adherence to portabil-
               ity concerns shouldn't get in(1,8) the way of your getting your job

               OPERATION is one of LOCK_SH, LOCK_EX, or LOCK_UN, possibly com-
               bined with LOCK_NB.  These constants are traditionally valued
               1, 2, 8 and 4, but you can use the symbolic names if(3,n) you import
               them from the Fcntl module, either individually, or as a group
               using the ':flock' tag.  LOCK_SH requests a shared lock,
               LOCK_EX requests an exclusive lock, and LOCK_UN releases a pre-
               viously requested lock.  If LOCK_NB is bitwise-or'ed with
               LOCK_SH or LOCK_EX then "flock(1,2)" will return immediately rather
               than blocking waiting for the lock (check the return status to
               see if(3,n) you got it).

               To avoid the possibility of miscoordination, Perl now flushes
               FILEHANDLE before locking or unlocking it.

               Note that the emulation built with lockf(3) doesn't provide
               shared locks, and it requires that FILEHANDLE be open(2,3,n) with
               write(1,2) intent.  These are the semantics that lockf(3) imple-
               ments.  Most if(3,n) not all systems implement lockf(3) in(1,8) terms of
               fcntl(2) locking, though, so the differing semantics shouldn't
               bite too many people.

               Note that the fcntl(2) emulation of flock(1,2)(3) requires that
               FILEHANDLE be open(2,3,n) with read(2,n,1 builtins) intent to use LOCK_SH and requires
               that it be open(2,3,n) with write(1,2) intent to use LOCK_EX.

               Note also that some versions of "flock(1,2)" cannot lock things over
               the network; you would need to use the more system-specific
               "fcntl" for that.  If you like you can force Perl to ignore
               your system's flock(1,2)(2) function, and so provide its own
               fcntl(2)-based emulation, by passing the switch(1,n) "-Ud_flock" to
               the Configure program when you configure perl.

               Here's a mailbox appender for BSD systems.

                   use Fcntl ':flock'; # import LOCK_* constants

                   sub lock {
                       # and, in(1,8) case someone appended
                       # while we were waiting...
                       seek(MBOX, 0, 2);

                   sub unlock {

                   open(2,3,n)(MBOX, ">>/usr/spool/mail(1,8)/$ENV{'USER'}")
                           or die "Can't open(2,3,n) mailbox: $!";

                   print MBOX $msg,"\n\n";

               On systems that support a real flock(1,2)(), locks are inherited
               across fork() calls, whereas those that must resort to the more
               capricious fcntl() function lose the locks, making it harder to
               write(1,2) servers.

               See also DB_File for other flock(1,2)() examples.

       fork    Does a fork(2) system call to create a new process running the
               same program at the same point.  It returns the child pid to
               the parent process, 0 to the child process, or "undef" if(3,n) the
               fork is unsuccessful.  File descriptors (and sometimes locks on
               those descriptors) are shared, while everything else is copied.
               On most systems supporting fork(), great care has gone into
               making it extremely efficient (for example, using copy-on-write
               technology on data pages), making it the dominant paradigm for
               multitasking over the last few decades.

               Beginning with v5.6.0, Perl will attempt to flush(8,n) all files
               opened for output before forking the child process, but this
               may not be supported on some platforms (see perlport).  To be
               safe, you may need to set(7,n,1 builtins) $| ($AUTOFLUSH in(1,8) English) or call
               the "autoflush()" method of "IO::Handle" on any open(2,3,n) handles in(1,8)
               order to avoid duplicate output.

               If you "fork" without ever waiting on your children, you will
               accumulate zombies.  On some systems, you can avoid this by
               setting $SIG{CHLD} to "IGNORE".  See also perlipc for more
               examples of forking and reaping moribund children.

               Note that if(3,n) your forked child inherits system file(1,n) descriptors
               like STDIN and STDOUT that are actually connected by a pipe(2,8) or
               socket(2,7,n), even if(3,n) you exit(3,n,1 builtins), then the remote server (such as, say,
               a CGI script or a backgrounded job launched from a remote
               shell) won't think you're done.  You should reopen those to
               /dev/null if(3,n) it's any issue.

       format  Declare a picture format for use by the "write(1,2)" function.  For

                   format Something =
                       Test: @<<<<<<<< @||||| @>>>>>
                             $str,     $%,    '$' . int($num)

                   $str = "widget";
                   $num = $cost/$quantity;
                   $~ = 'Something';

               See perlform for many details and examples.

       formline PICTURE,LIST
               This is an internal function used by "format"s, though you may
               call it, too.  It formats (see perlform) a list of values
               according to the contents of PICTURE, placing the output into
               the format output accumulator, $^A (or $ACCUMULATOR in(1,8)
               English).  Eventually, when a "write(1,2)" is done, the contents of
               $^A are written to some filehandle, but you could also read(2,n,1 builtins) $^A
               yourself and then set(7,n,1 builtins) $^A back to "".  Note that a format typi-
               cally does one "formline" per line of form, but the "formline"
               function itself doesn't care how many newlines are embedded in(1,8)
               the PICTURE.  This means that the "~" and "~~" tokens will
               treat the entire PICTURE as a single line.  You may therefore
               need to use multiple formlines to implement a single record
               format, just like the format compiler.

               Be careful if(3,n) you put double quotes around the picture, because
               an "@" character may be taken to mean the beginning of an array
               name.  "formline" always returns true.  See perlform for other

       getc FILEHANDLE
       getc    Returns the next character from the input file(1,n) attached to
               FILEHANDLE, or the undefined value at end of file(1,n), or if(3,n) there
               was an error(8,n) (in(1,8) the latter case $! is set(7,n,1 builtins)).  If FILEHANDLE is
               omitted, reads from STDIN.  This is not particularly efficient.
               However, it cannot be used by itself to fetch single characters
               without waiting for the user to hit enter.  For that, try some-
               thing more like:

                   if(3,n) ($BSD_STYLE) {
                       system "stty cbreak </dev/tty(1,4) >/dev/tty(1,4) 2>&1";
                   else {
                       system "stty", '-icanon', 'eol', "\001";

                   $key = getc(STDIN);

                   if(3,n) ($BSD_STYLE) {
                       system "stty -cbreak </dev/tty(1,4) >/dev/tty(1,4) 2>&1";
                   else {
                       system "stty", 'icanon', 'eol', '^@'; # ASCII null
                   print "\n";

               Determination of whether $BSD_STYLE should be set(7,n,1 builtins) is left as an
               exercise to the reader.

               The "POSIX::getattr" function can do this more portably on sys-
               tems purporting POSIX compliance.  See also the "Term::ReadKey"
               module from your nearest CPAN site; details on CPAN can be
               found on "CPAN" in(1,8) perlmodlib.

               Implements the C library function of the same name, which on
               most systems returns the current login(1,3,5) from /etc/utmp, if(3,n) any.
               If null, use "getpwuid".

                   $login(1,3,5) = getlogin || getpwuid($<) || "Kilroy";

               Do not consider "getlogin" for authentication: it is not as
               secure as "getpwuid".

       getpeername(1,2) SOCKET
               Returns the packed sockaddr address of other end of the SOCKET

                   use Socket;
                   $hersockaddr    = getpeername(1,2)(SOCK);
                   ($port, $iaddr) = sockaddr_in($hersockaddr);
                   $herhostname    = gethostbyaddr($iaddr, AF_INET);
                   $herstraddr     = inet_ntoa($iaddr);

       getpgrp PID
               Returns the current process group for the specified PID.  Use a
               PID of 0 to get the current process group for the current
               process.  Will raise(3,n) an exception if(3,n) used on a machine that
               doesn't implement getpgrp(2).  If PID is omitted, returns
               process group of current process.  Note that the POSIX version(1,3,5)
               of "getpgrp" does not accept(2,8) a PID argument, so only "PID==0"
               is truly portable.

       getppid Returns the process id of the parent process.

               Note for Linux users: on Linux, the C functions "getpid()" and
               "getppid()" return different values from different threads. In
               order to be portable, this behavior is not reflected by the
               perl-level function "getppid()", that returns a consistent
               value across threads. If you want to call the underlying "getp-
               pid()", you may use the CPAN module "Linux::Pid".

       getpriority WHICH,WHO
               Returns the current priority for a process, a process group, or
               a user.  (See getpriority(2).)  Will raise(3,n) a fatal exception if(3,n)
               used on a machine that doesn't implement getpriority(2).

       getpwnam NAME
       getgrnam NAME
       gethostbyname NAME
       getnetbyname NAME
       getprotobyname NAME
       getpwuid UID
       getgrgid GID
       getservbyname NAME,PROTO
       gethostbyaddr ADDR,ADDRTYPE
       getnetbyaddr ADDR,ADDRTYPE
       getprotobynumber NUMBER
       getservbyport PORT,PROTO
       sethostent STAYOPEN
       setnetent STAYOPEN
       setprotoent STAYOPEN
       setservent STAYOPEN
               These routines perform the same functions as their counterparts
               in(1,8) the system library.  In list context, the return values from
               the various get routines are as follows:

                      $quota(1,8),$comment,$gcos,$dir,$shell,$expire) = getpw*
                   ($name,$passwd(1,5),$gid,$members) = getgr*
                   ($name,$aliases,$addrtype,$length,@addrs) = gethost*
                   ($name,$aliases,$addrtype,$net) = getnet*
                   ($name,$aliases,$proto) = getproto*
                   ($name,$aliases,$port,$proto) = getserv*

               (If the entry doesn't exist you get a null list.)

               The exact meaning of the $gcos field varies but it usually con-
               tains the real name of the user (as opposed to the login(1,3,5) name)
               and other information pertaining to the user.  Beware, however,
               that in(1,8) many system users(1,5) are able to change this information
               and therefore it cannot be trusted and therefore the $gcos is
               tainted (see perlsec).  The $passwd(1,5) and $shell, user's
               encrypted password and login(1,3,5) shell, are also tainted, because
               of the same reason.

               In scalar context, you get the name, unless the function was a
               lookup by name, in(1,8) which case you get the other thing, whatever
               it is.  (If the entry doesn't exist you get the undefined
               value.)  For example:

                   $uid   = getpwnam($name);
                   $name  = getpwuid($num);
                   $name  = getpwent();
                   $gid   = getgrnam($name);
                   $name  = getgrgid($num);
                   $name  = getgrent();

               In getpw*() the fields $quota(1,8), $comment, and $expire are spe-
               cial cases in(1,8) the sense that in(1,8) many systems they are unsup-
               ported.  If the $quota(1,8) is unsupported, it is an empty scalar.
               If it is supported, it usually encodes the disk quota.  If the
               $comment field is unsupported, it is an empty scalar.  If it is
               supported it usually encodes some administrative comment about
               the user.  In some systems the $quota(1,8) field may be $change or
               $age, fields that have to do with password aging.  In some sys-
               tems the $comment field may be $class.  The $expire field, if(3,n)
               present, encodes the expiration period of the account or the
               password.  For the availability and the exact meaning of these
               fields in(1,8) your system, please consult your getpwnam(3) documen-
               tation and your pwd.h file.  You can also find out from within
               Perl what your $quota(1,8) and $comment fields mean and whether you
               have the $expire field by using the "Config" module and the
               values "d_pwquota", "d_pwage", "d_pwchange", "d_pwcomment", and
               "d_pwexpire".  Shadow password files are only supported if(3,n) your
               vendor has implemented them in(1,8) the intuitive fashion that call-
               ing the regular C library routines gets(3,n) the shadow(3,5) versions if(3,n)
               you're running under privilege or if(3,n) there exists the shadow(3,5)(3)
               functions as found in(1,8) System V ( this includes Solaris and
               Linux.)  Those systems which implement a proprietary shadow(3,5)
               password facility are unlikely to be supported.

               The $members value returned by getgr*() is a space separated
               list of the login(1,3,5) names of the members of the group.

               For the gethost*() functions, if(3,n) the "h_errno" variable is sup-
               ported in(1,8) C, it will be returned to you via $? if(3,n) the function
               call fails.  The @addrs value returned by a successful call is
               a list of the raw(3x,7,8,3x cbreak) addresses returned by the corresponding sys-
               tem library call.  In the Internet domain, each address is four
               bytes long and you can unpack it by saying something like:

                   ($a,$b,$c,$d) = unpack('C4',$addr[0]);

               The Socket library makes this slightly easier:

                   use Socket;
                   $iaddr = inet_aton("127.1"); # or whatever address
                   $name  = gethostbyaddr($iaddr, AF_INET);

                   # or going the other way
                   $straddr = inet_ntoa($iaddr);

               If you get tired of remembering which element of the return
               list contains which return value, by-name interfaces are pro-
               vided in(1,8) standard modules: "File::stat", "Net::hostent",
               "Net::netent", "Net::protoent", "Net::servent", "Time::gmtime",
               "Time::localtime", and "User::grent".  These override the nor-
               mal built-ins, supplying versions that return objects with the
               appropriate names for each field.  For example:

                  use File::stat;
                  use User::pwent;
                  $is_his = (stat(1,2)($filename)->uid == pwent($whoever)->uid);

               Even though it looks like they're the same method calls (uid),
               they aren't, because a "File::stat" object is different from a
               "User::pwent" object.

       getsockname SOCKET
               Returns the packed sockaddr address of this end of the SOCKET
               connection, in(1,8) case you don't know the address because you have
               several different IPs that the connection might have come in(1,8)

                   use Socket;
                   $mysockaddr = getsockname(SOCK);
                   ($port, $myaddr) = sockaddr_in($mysockaddr);
                   printf(1,3,1 builtins) "Connect to %s [%s]\n",
                      scalar gethostbyaddr($myaddr, AF_INET),

       getsockopt SOCKET,LEVEL,OPTNAME
               Queries the option named(5,8) OPTNAME associated with SOCKET at a
               given LEVEL.  Options may exist at multiple protocol levels
               depending on the socket(2,7,n) type, but at least the uppermost socket(2,7,n)
               level SOL_SOCKET (defined in(1,8) the "Socket" module) will exist.
               To query options at another level the protocol number of the
               appropriate protocol controlling the option should be supplied.
               For example, to indicate that an option is to be interpreted by
               the TCP protocol, LEVEL should be set(7,n,1 builtins) to the protocol number of
               TCP, which you can get using getprotobyname.

               The call returns a packed string(3,n) representing the requested
               socket(2,7,n) option, or "undef" if(3,n) there is an error(8,n) (the error(8,n) rea-
               son will be in(1,8) $!). What exactly is in(1,8) the packed string(3,n)
               depends in(1,8) the LEVEL and OPTNAME, consult your system documen-
               tation for details. A very common case however is that the
               option is an integer, in(1,8) which case the result will be an
               packed integer which you can decode using unpack with the "i"
               (or "I") format.

               An example testing if(3,n) Nagle's algorithm is turned on on a

                   use Socket;

                   defined(my $tcp = getprotobyname("tcp"))
                       or die "Could not determine the protocol number for tcp";
                   # my $tcp = Socket::IPPROTO_TCP; # Alternative
                   my $packed = getsockopt($socket(2,7,n), $tcp, Socket::TCP_NODELAY)
                       or die "Could not query TCP_NODELAY SOCKEt option: $!";
                   my $nodelay = unpack("I", $packed);
                   print "Nagle's algorithm is turned ", $nodelay ? "off\n" : "on\n";

       glob(1,3,7,n) EXPR
       glob(1,3,7,n)    In list context, returns a (possibly empty) list of filename
               expansions on the value of EXPR such as the standard Unix shell
               /bin/csh would do. In scalar context, glob(1,3,7,n) iterates through
               such filename expansions, returning undef when the list is
               exhausted. This is the internal function implementing the
               "<*.c>" operator, but you can use it directly. If EXPR is omit-
               ted, $_ is used.  The "<*.c>" operator is discussed in(1,8) more
               detail in(1,8) "I/O Operators" in(1,8) perlop.

               Beginning with v5.6.0, this operator is implemented using the
               standard "File::Glob" extension.  See File::Glob for details.

       gmtime EXPR
               Converts a time(1,2,n) as returned by the time(1,2,n) function to an 8-ele-
               ment list with the time(1,2,n) localized for the standard Greenwich
               time(1,2,n) zone.  Typically used as follows:

                   #  0    1    2     3     4    5     6     7
                   ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday) =

               All list elements are numeric, and come straight out of the C
               `struct tm'.  $sec, $min, and $hour are the seconds, minutes,
               and hours of the specified time.  $mday is the day of the
               month, and $mon is the month itself, in(1,8) the range 0..11 with 0
               indicating January and 11 indicating December.  $year is the
               number of years since 1900.  That is, $year is 123 in(1,8) year
               2023.  $wday is the day of the week, with 0 indicating Sunday
               and 3 indicating Wednesday.  $yday is the day of the year, in(1,8)
               the range 0..364 (or 0..365 in(1,8) leap years.)

               Note that the $year element is not simply the last two digits
               of the year.  If you assume it is, then you create non-Y2K-com-
               pliant programs--and you wouldn't want to do that, would you?

               The proper way to get a complete 4-digit year is simply:

                       $year += 1900;

               And to get the last two digits of the year (e.g., '01' in(1,8) 2001)

                       $year = sprintf("%02d", $year % 100);

               If EXPR is omitted, "gmtime()" uses the current time(1,2,n)

               In scalar context, "gmtime()" returns the ctime(3) value:

                   $now_string = gmtime;  # e.g., "Thu Oct 13 04:54:34 1994"

               If you need local time(1,2,n) instead of GMT use the "localtime"
               builtin.  See also the "timegm" function provided by the
               "Time::Local" module, and the strftime(3) and mktime(3) func-
               tions available via the POSIX module.

               This scalar value is not locale(3,5,7) dependent (see perllocale), but
               is instead a Perl builtin.  To get somewhat similar but locale(3,5,7)
               dependent date strings, see the example in(1,8) "localtime".

       goto LABEL
       goto EXPR
       goto &NAME
               The "goto-LABEL" form finds the statement labeled with LABEL
               and resumes execution there.  It may not be used to go into any
               construct that requires initialization, such as a subroutine or
               a "foreach" loop.  It also can't be used to go into a construct
               that is optimized away, or to get out of a block or subroutine
               given to "sort(1,3)".  It can be used to go almost anywhere else
               within the dynamic scope, including out of subroutines, but
               it's usually better to use some other construct such as "last"
               or "die".  The author of Perl has never felt the need to use
               this form of "goto" (in(1,8) Perl, that is--C is another matter).
               (The difference being that C does not offer named(5,8) loops com-
               bined with loop control.  Perl does, and this replaces most
               structured uses of "goto" in(1,8) other languages.)

               The "goto-EXPR" form expects a label name, whose scope will be
               resolved dynamically.  This allows for computed "goto"s per
               FORTRAN, but isn't necessarily recommended if(3,n) you're optimizing
               for maintainability:

                   goto ("FOO", "BAR", "GLARCH")[$i];

               The "goto-&NAME" form is quite different from the other forms
               of "goto".  In fact, it isn't a goto in(1,8) the normal sense at
               all, and doesn't have the stigma associated with other gotos.
               Instead, it exits the current subroutine (losing any changes
               set(7,n,1 builtins) by local()) and immediately calls in(1,8) its place the named(5,8)
               subroutine using the current value of @_.  This is used by
               "AUTOLOAD" subroutines that wish to load(7,n) another subroutine and
               then pretend that the other subroutine had been called in(1,8) the
               first place (except that any modifications to @_ in(1,8) the current
               subroutine are propagated to the other subroutine.)  After the
               "goto", not even "caller" will be able to tell that this rou-
               tine was called first.

               NAME needn't be the name of a subroutine; it can be a scalar
               variable containing a code reference, or a block which evalu-
               ates to a code reference.

       grep BLOCK LIST
       grep EXPR,LIST
               This is similar in(1,8) spirit to, but not the same as, grep(1) and
               its relatives.  In particular, it is not limited to using regu-
               lar expressions.

               Evaluates the BLOCK or EXPR for each element of LIST (locally
               setting $_ to each element) and returns the list value consist-
               ing of those elements for which the expression evaluated to
               true.  In scalar context, returns the number of times the
               expression was true.

                   @foo = grep(!/^#/, @bar);    # weed out comments

               or equivalently,

                   @foo = grep {!/^#/} @bar;    # weed out comments

               Note that $_ is an alias to the list value, so it can be used
               to modify the elements of the LIST.  While this is useful and
               supported, it can cause bizarre results if(3,n) the elements of LIST
               are not variables.  Similarly, grep returns aliases into the
               original list, much as a for loop's index variable aliases the
               list elements.  That is, modifying an element of a list
               returned by grep (for example, in(1,8) a "foreach", "map" or another
               "grep") actually modifies the element in(1,8) the original list.
               This is usually something to be avoided when writing clear(1,3x,3x clrtobot)

               See also "map" for a list composed of the results of the BLOCK
               or EXPR.

       hex EXPR
       hex     Interprets EXPR as a hex string(3,n) and returns the corresponding
               value.  (To convert strings that might start with either 0, 0x,
               or 0b, see "oct".)  If EXPR is omitted, uses $_.

                   print hex '0xAf'; # prints '175'
                   print hex 'aF';   # same

               Hex strings may only represent integers.  Strings that would
               cause integer overflow trigger a warning.  Leading whitespace
               is not stripped, unlike oct().

       import  There is no builtin "import" function.  It is just an ordinary
               method (subroutine) defined (or inherited) by modules that wish
               to export names to another module.  The "use" function calls
               the "import" method for the package used.  See also "use",
               perlmod, and Exporter.

       index STR,SUBSTR
               The index function searches for one string(3,n) within another, but
               without the wildcard-like behavior of a full regular-expression
               pattern match.  It returns the position of the first occurrence
               of SUBSTR in(1,8) STR at or after POSITION.  If POSITION is omitted,
               starts searching from the beginning of the string.  The return
               value is based at 0 (or whatever you've set(7,n,1 builtins) the $[ variable
               to--but don't do that).  If the substring is not found, returns
               one less(1,3) than the base, ordinarily "-1".

       int EXPR
       int     Returns the integer portion of EXPR.  If EXPR is omitted, uses
               $_.  You should not use this function for rounding: one because
               it truncates towards 0, and two because machine representations
               of floating point numbers can sometimes produce counterintu-
               itive results.  For example, "int(-6.725/0.025)" produces -268
               rather than the correct -269; that's because it's really more
               like -268.99999999999994315658 instead.  Usually, the
               "sprintf", "printf(1,3,1 builtins)", or the "POSIX::floor" and "POSIX::ceil"
               functions will serve you better than will int().

               Implements the ioctl(2) function.  You'll probably first have
               to say

                   require ""; # probably in(1,8) /usr/local/lib/perl/

               to get the correct function definitions.  If doesn't
               exist or doesn't have the correct definitions you'll have to
               roll your own, based on your C header files such as
               <sys/ioctl.h>.  (There is a Perl script called h2ph that comes
               with the Perl kit that may help you in(1,8) this, but it's nontriv-
               ial.)  SCALAR will be read(2,n,1 builtins) and/or written depending on the
               FUNCTION--a pointer to the string(3,n) value of SCALAR will be
               passed as the third argument of the actual "ioctl" call.  (If
               SCALAR has no string(3,n) value but does have a numeric value, that
               value will be passed rather than a pointer to the string(3,n) value.
               To guarantee this to be true, add a 0 to the scalar before
               using it.)  The "pack(3,n,n pack-old)" and "unpack" functions may be needed to
               manipulate the values of structures used by "ioctl".

               The return value of "ioctl" (and "fcntl") is as follows:

                       if(3,n) OS returns:          then Perl returns:
                           -1                    undefined value
                            0                  string(3,n) "0 but true"
                       anything else               that number

               Thus Perl returns true on success and false on failure, yet you
               can still easily determine the actual value returned by the
               operating system:

                   $retval = ioctl(...) || -1;
                   printf(1,3,1 builtins) "System returned %d\n", $retval;

               The special string(3,n) "0 but true" is exempt from -w complaints
               about improper numeric conversions.

       join(1,n) EXPR,LIST
               Joins the separate strings of LIST into a single string(3,n) with
               fields separated by the value of EXPR, and returns that new
               string.  Example:

                   $rec = join(1,n)(':', $login(1,3,5),$passwd(1,5),$uid,$gid,$gcos,$home,$shell);

               Beware that unlike "split(1,n)", "join(1,n)" doesn't take a pattern as
               its first argument.  Compare "split(1,n)".

       keys HASH
               Returns a list consisting of all the keys of the named(5,8) hash.
               (In scalar context, returns the number of keys.)

               The keys are returned in(1,8) an apparently random(3,4,6) order.  The
               actual random(3,4,6) order is subject to change in(1,8) future versions of
               perl, but it is guaranteed to be the same order as either the
               "values" or "each" function produces (given that the hash has
               not been modified).  Since Perl 5.8.1 the ordering is different
               even between different runs of Perl for security reasons (see
               "Algorithmic Complexity Attacks" in(1,8) perlsec).

               As a side effect, calling keys() resets the HASH's internal
               iterator, see "each". (In particular, calling keys() in(1,8) void
               context resets the iterator with no other overhead.)

               Here is yet another way to print your environment:

                   @keys = keys %ENV;
                   @values = values %ENV;
                   while (@keys) {
                       print pop(@keys), '=', pop(@values), "\n";

               or how about sorted by key:

                   foreach $key (sort(1,3)(keys %ENV)) {
                       print $key, '=', $ENV{$key}, "\n";

               The returned values are copies of the original keys in(1,8) the
               hash, so modifying them will not affect the original hash.
               Compare "values".

               To sort(1,3) a hash by value, you'll need to use a "sort(1,3)" function.
               Here's a descending numeric sort(1,3) of a hash by its values:

                   foreach $key (sort(1,3) { $hash{$b} <=> $hash{$a} } keys %hash) {
                       printf(1,3,1 builtins) "%4d %s\n", $hash{$key}, $key;

               As an lvalue "keys" allows you to increase the number of hash
               buckets allocated for the given hash.  This can gain you a mea-
               sure of efficiency if(3,n) you know the hash is going to get big.
               (This is similar to pre-extending an array by assigning a
               larger number to $#array.)  If you say

                   keys %hash = 200;

               then %hash will have at least 200 buckets allocated for it--256
               of them, in(1,8) fact, since it rounds up to the next power of two.
               These buckets will be retained even if(3,n) you do "%hash = ()", use
               "undef %hash" if(3,n) you want to free the storage while %hash is
               still in(1,8) scope.  You can't shrink the number of buckets allo-
               cated for the hash using "keys" in(1,8) this way (but you needn't
               worry about doing this by accident, as trying has no effect).

               See also "each", "values" and "sort(1,3)".

       kill(1,2,1 builtins) SIGNAL, LIST
               Sends a signal(2,7) to a list of processes.  Returns the number of
               processes successfully signaled (which is not necessarily the
               same as the number actually killed).

                   $cnt = kill(1,2,1 builtins) 1, $child1, $child2;
                   kill(1,2,1 builtins) 9, @goners;

               If SIGNAL is zero, no signal(2,7) is sent to the process.  This is a
               useful way to check that a child process is alive and hasn't
               changed its UID.  See perlport for notes on the portability of
               this construct.

               Unlike in(1,8) the shell, if(3,n) SIGNAL is negative, it kills process
               groups instead of processes.  (On System V, a negative PROCESS
               number will also kill(1,2,1 builtins) process groups, but that's not portable.)
               That means you usually want to use positive not negative sig-
               nals.  You may also use a signal(2,7) name in(1,8) quotes.

               See "Signals" in(1,8) perlipc for more details.

       last LABEL
       last    The "last" command is like the "break" statement in(1,8) C (as used
               in(1,8) loops); it immediately exits the loop in(1,8) question.  If the
               LABEL is omitted, the command refers to the innermost enclosing
               loop.  The "continue" block, if(3,n) any, is not executed:

                   LINE: while (<STDIN>) {
                       last LINE if(3,n) /^$/;      # exit(3,n,1 builtins) when done with header

               "last" cannot be used to exit(3,n,1 builtins) a block which returns a value
               such as "eval {}", "sub {}" or "do {}", and should not be used
               to exit(3,n,1 builtins) a grep() or map() operation.

               Note that a block by itself is semantically identical to a loop
               that executes once.  Thus "last" can be used to effect an early
               exit(3,n,1 builtins) out of such a block.

               See also "continue" for an illustration of how "last", "next",
               and "redo" work.

       lc EXPR
       lc      Returns a lowercased version(1,3,5) of EXPR.  This is the internal
               function implementing the "\L" escape in(1,8) double-quoted strings.
               Respects current LC_CTYPE locale(3,5,7) if(3,n) "use locale(3,5,7)" in(1,8) force.  See
               perllocale and perlunicode for more details about locale(3,5,7) and
               Unicode support.

               If EXPR is omitted, uses $_.

       lcfirst EXPR
       lcfirst Returns the value of EXPR with the first character lowercased.
               This is the internal function implementing the "\l" escape in(1,8)
               double-quoted strings.  Respects current LC_CTYPE locale(3,5,7) if(3,n)
               "use locale(3,5,7)" in(1,8) force.  See perllocale and perlunicode for more
               details about locale(3,5,7) and Unicode support.

               If EXPR is omitted, uses $_.

       length EXPR
       length  Returns the length in(1,8) characters of the value of EXPR.  If EXPR
               is omitted, returns length of $_.  Note that this cannot be
               used on an entire array or hash to find out how many elements
               these have.  For that, use "scalar @array" and "scalar keys
               %hash" respectively.

               Note the characters: if(3,n) the EXPR is in(1,8) Unicode, you will get
               the number of characters, not the number of bytes.  To get the
               length in(1,8) bytes, use "do { use bytes; length(EXPR) }", see

       link(1,2) OLDFILE,NEWFILE
               Creates a new filename linked to the old filename.  Returns
               true for success, false otherwise.

       listen(1,2,7) SOCKET,QUEUESIZE
               Does the same thing that the listen(1,2,7) system call does.  Returns
               true if(3,n) it succeeded, false otherwise.  See the example in(1,8)
               "Sockets: Client/Server Communication" in(1,8) perlipc.

       local EXPR
               You really probably want to be using "my" instead, because
               "local" isn't what most people think of as "local".  See "Pri-
               vate Variables via my()" in(1,8) perlsub for details.

               A local modifies the listed variables to be local to the
               enclosing block, file(1,n), or eval.  If more than one value is
               listed, the list must be placed in(1,8) parentheses.  See "Temporary
               Values via local()" in(1,8) perlsub for details, including issues
               with tied arrays and hashes.

       localtime EXPR
               Converts a time(1,2,n) as returned by the time(1,2,n) function to a 9-element
               list with the time(1,2,n) analyzed for the local time(1,2,n) zone.  Typically
               used as follows:

                   #  0    1    2     3     4    5     6     7     8
                   ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =

               All list elements are numeric, and come straight out of the C
               `struct tm'.  $sec, $min, and $hour are the seconds, minutes,
               and hours of the specified time.  $mday is the day of the
               month, and $mon is the month itself, in(1,8) the range 0..11 with 0
               indicating January and 11 indicating December.  $year is the
               number of years since 1900.  That is, $year is 123 in(1,8) year
               2023.  $wday is the day of the week, with 0 indicating Sunday
               and 3 indicating Wednesday.  $yday is the day of the year, in(1,8)
               the range 0..364 (or 0..365 in(1,8) leap years.)  $isdst is true if(3,n)
               the specified time(1,2,n) occurs during daylight savings time(1,2,n), false

               Note that the $year element is not simply the last two digits
               of the year.  If you assume it is, then you create non-Y2K-com-
               pliant programs--and you wouldn't want to do that, would you?

               The proper way to get a complete 4-digit year is simply:

                       $year += 1900;

               And to get the last two digits of the year (e.g., '01' in(1,8) 2001)

                       $year = sprintf("%02d", $year % 100);

               If EXPR is omitted, "localtime()" uses the current time(1,2,n)

               In scalar context, "localtime()" returns the ctime(3) value:

                   $now_string = localtime;  # e.g., "Thu Oct 13 04:54:34 1994"

               This scalar value is not locale(3,5,7) dependent but is a Perl
               builtin. For GMT instead of local time(1,2,n) use the "gmtime"
               builtin. See also the "Time::Local" module (to convert the sec-
               ond, minutes, hours, ... back to the integer value returned by
               time(1,2,n)()), and the POSIX module's strftime(3) and mktime(3) func-

               To get somewhat similar but locale(3,5,7) dependent date strings, set(7,n,1 builtins)
               up your locale(3,5,7) environment variables appropriately (please see
               perllocale) and try for example:

                   use POSIX qw(strftime);
                   $now_string = strftime "%a %b %e %H:%M:%S %Y", localtime;
                   # or for GMT formatted appropriately for your locale:
                   $now_string = strftime "%a %b %e %H:%M:%S %Y", gmtime;

               Note that the %a and %b, the short forms of the day of the week
               and the month of the year, may not necessarily be three charac-
               ters wide.

       lock THING
               This function places an advisory lock on a shared variable, or
               referenced object contained in(1,8) THING until the lock goes out of

               lock() is a "weak keyword" : this means that if(3,n) you've defined
               a function by this name (before any calls to it), that function
               will be called instead. (However, if(3,n) you've said "use threads",
               lock() is always a keyword.) See threads.

       log EXPR
       log     Returns the natural logarithm (base e) of EXPR.  If EXPR is
               omitted, returns log of $_.  To get the log of another base,
               use basic algebra: The base-N log of a number is equal to the
               natural log of that number divided by the natural log of N.
               For example:

                   sub log10 {
                       my $n = shift;
                       return log($n)/log(10);

               See also "exp" for the inverse operation.

       lstat EXPR
       lstat   Does the same thing as the "stat(1,2)" function (including setting
               the special "_" filehandle) but stats a symbolic link(1,2) instead
               of the file(1,n) the symbolic link(1,2) points to.  If symbolic links are
               unimplemented on your system, a normal "stat(1,2)" is done.  For
               much more detailed information, please see the documentation
               for "stat(1,2)".

               If EXPR is omitted, stats $_.

       m//     The match operator.  See perlop.

       map BLOCK LIST
       map EXPR,LIST
               Evaluates the BLOCK or EXPR for each element of LIST (locally
               setting $_ to each element) and returns the list value composed
               of the results of each such evaluation.  In scalar context,
               returns the total number of elements so generated.  Evaluates
               BLOCK or EXPR in(1,8) list context, so each element of LIST may pro-
               duce zero, one, or more elements in(1,8) the returned value.

                   @chars = map(chr, @nums);

               translates a list of numbers to the corresponding characters.

                   %hash = map { getkey($_) => $_ } @array;

               is just a funny way to write(1,2)

                   %hash = ();
                   foreach $_ (@array) {
                       $hash{getkey($_)} = $_;

               Note that $_ is an alias to the list value, so it can be used
               to modify the elements of the LIST.  While this is useful and
               supported, it can cause bizarre results if(3,n) the elements of LIST
               are not variables.  Using a regular "foreach" loop for this
               purpose would be clearer in(1,8) most cases.  See also "grep" for an
               array composed of those items of the original list for which
               the BLOCK or EXPR evaluates to true.

               "{" starts both hash references and blocks, so "map { ..."
               could be either the start of map BLOCK LIST or map EXPR, LIST.
               Because perl doesn't look(1,8,3 Search::Dict) ahead for the closing "}" it has to
               take a guess at which its dealing with based what it finds just
               after the "{". Usually it gets(3,n) it right, but if(3,n) it doesn't it
               won't realize something is wrong until it gets(3,n) to the "}" and
               encounters the missing (or unexpected) comma. The syntax error(8,n)
               will be reported close(2,7,n) to the "}" but you'll need to change
               something near the "{" such as using a unary "+" to give perl
               some help:

                   %hash = map {  "\L$_", 1  } @array  # perl guesses EXPR.  wrong
                   %hash = map { +"\L$_", 1  } @array  # perl guesses BLOCK. right
                   %hash = map { ("\L$_", 1) } @array  # this also works
                   %hash = map {  lc($_), 1  } @array  # as does this.
                   %hash = map +( lc($_), 1 ), @array  # this is EXPR and works!

                   %hash = map  ( lc($_), 1 ), @array  # evaluates to (1, @array)

               or to force an anon hash constructor use "+{"

                  @hashes = map +{ lc($_), 1 }, @array # EXPR, so needs , at end

               and you get list of anonymous hashes each with only 1 entry.

       mkdir(1,2) FILENAME,MASK
       mkdir(1,2) FILENAME
               Creates the directory specified by FILENAME, with permissions
               specified by MASK (as modified by "umask").  If it succeeds it
               returns true, otherwise it returns false and sets $! (errno).
               If omitted, MASK defaults to 0777.

               In general, it is better to create directories with permissive
               MASK, and let the user modify that with their "umask", than it
               is to supply a restrictive MASK and give the user no way to be
               more permissive.  The exceptions to this rule are when the file(1,n)
               or directory should be kept private (mail(1,8) files, for instance).
               The perlfunc(1) entry on "umask" discusses the choice of MASK
               in(1,8) more detail.

               Note that according to the POSIX 1003.1-1996 the FILENAME may
               have any number of trailing slashes.  Some operating and
               filesystems do not get this right, so Perl automatically
               removes all trailing slashes to keep everyone happy.

       msgctl ID,CMD,ARG
               Calls the System V IPC function msgctl(2).  You'll probably
               have to say

                   use IPC::SysV;

               first to get the correct constant definitions.  If CMD is
               "IPC_STAT", then ARG must be a variable which will hold the
               returned "msqid_ds" structure.  Returns like "ioctl": the unde-
               fined value for error(8,n), "0 but true" for zero, or the actual
               return value otherwise.  See also "SysV IPC" in(1,8) perlipc,
               "IPC::SysV", and "IPC::Semaphore" documentation.

       msgget KEY,FLAGS
               Calls the System V IPC function msgget(2).  Returns the message
               queue(1,3) id, or the undefined value if(3,n) there is an error.  See
               also "SysV IPC" in(1,8) perlipc and "IPC::SysV" and "IPC::Msg" docu-

       msgrcv ID,VAR,SIZE,TYPE,FLAGS
               Calls the System V IPC function msgrcv to receive a message
               from message queue(1,3) ID into variable VAR with a maximum message
               size of SIZE.  Note that when a message is received, the mes-
               sage type as a native long integer will be the first thing in(1,8)
               VAR, followed by the actual message.  This packing may be
               opened with "unpack("l! a*")".  Taints the variable.  Returns
               true if(3,n) successful, or false if(3,n) there is an error.  See also
               "SysV IPC" in(1,8) perlipc, "IPC::SysV", and "IPC::SysV::Msg" docu-

       msgsnd ID,MSG,FLAGS
               Calls the System V IPC function msgsnd to send(2,n) the message MSG
               to the message queue(1,3) ID.  MSG must begin with the native long
               integer message type, and be followed by the length of the
               actual message, and finally the message itself.  This kind of
               packing can be achieved with "pack(3,n,n pack-old)("l! a*", $type, $message)".
               Returns true if(3,n) successful, or false if(3,n) there is an error.  See
               also "IPC::SysV" and "IPC::SysV::Msg" documentation.

       my EXPR
       my TYPE EXPR
       my EXPR : ATTRS
       my TYPE EXPR : ATTRS
               A "my" declares the listed variables to be local (lexically) to
               the enclosing block, file(1,n), or "eval".  If more than one value
               is listed, the list must be placed in(1,8) parentheses.

               The exact semantics and interface of TYPE and ATTRS are still
               evolving.  TYPE is currently bound to the use of "fields"
               pragma, and attributes are handled using the "attributes"
               pragma, or starting from Perl 5.8.0 also via the
               "Attribute::Handlers" module.  See "Private Variables via my()"
               in(1,8) perlsub for details, and fields, attributes, and

       next LABEL
       next    The "next" command is like the "continue" statement in(1,8) C; it
               starts the next iteration of the loop:

                   LINE: while (<STDIN>) {
                       next LINE if(3,n) /^#/;      # discard comments

               Note that if(3,n) there were a "continue" block on the above, it
               would get executed even on discarded lines.  If the LABEL is
               omitted, the command refers to the innermost enclosing loop.

               "next" cannot be used to exit(3,n,1 builtins) a block which returns a value
               such as "eval {}", "sub {}" or "do {}", and should not be used
               to exit(3,n,1 builtins) a grep() or map() operation.

               Note that a block by itself is semantically identical to a loop
               that executes once.  Thus "next" will exit(3,n,1 builtins) such a block early.

               See also "continue" for an illustration of how "last", "next",
               and "redo" work.

       no Module VERSION LIST
       no Module VERSION
       no Module LIST
       no Module
               See the "use" function, which "no" is the opposite of.

       oct EXPR
       oct     Interprets EXPR as an octal string(3,n) and returns the correspond-
               ing value.  (If EXPR happens to start off with "0x", interprets
               it as a hex string.  If EXPR starts off with "0b", it is inter-
               preted as a binary string.  Leading whitespace is ignored in(1,8)
               all three cases.)  The following will handle decimal, binary,
               octal, and hex in(1,8) the standard Perl or C notation:

                   $val = oct($val) if(3,n) $val =~ /^0/;

               If EXPR is omitted, uses $_.   To go the other way (produce a
               number in(1,8) octal), use sprintf() or printf(1,3,1 builtins)():

                   $perms = (stat(1,2)("filename"))[2] & 07777;
                   $oct_perms = sprintf "%lo", $perms;

               The oct() function is commonly used when a string(3,n) such as 644
               needs to be converted into a file(1,n) mode, for example. (Although
               perl will automatically convert strings into numbers as needed,
               this automatic conversion assumes base 10.)

       open(2,3,n) FILEHANDLE,EXPR
       open(2,3,n) FILEHANDLE,MODE,EXPR
       open(2,3,n) FILEHANDLE,MODE,EXPR,LIST
       open(2,3,n) FILEHANDLE
               Opens the file(1,n) whose filename is given by EXPR, and associates
               it with FILEHANDLE.

               (The following is a comprehensive reference to open(2,3,n)(): for a
               gentler introduction you may consider perlopentut.)

               If FILEHANDLE is an undefined scalar variable (or array or hash
               element) the variable is assigned a reference to a new anony-
               mous filehandle, otherwise if(3,n) FILEHANDLE is an expression, its
               value is used as the name of the real filehandle wanted.  (This
               is considered a symbolic reference, so "use strict 'refs'"
               should not be in(1,8) effect.)

               If EXPR is omitted, the scalar variable of the same name as the
               FILEHANDLE contains the filename.  (Note that lexical vari-
               ables--those declared with "my"--will not work for this pur-
               pose; so if(3,n) you're using "my", specify EXPR in(1,8) your call to

               If three or more arguments are specified then the mode of open-
               ing and the file(1,n) name are separate. If MODE is '<' or nothing,
               the file(1,n) is opened for input.  If MODE is '>', the file(1,n) is
               truncated and opened for output, being created if(3,n) necessary.
               If MODE is '>>', the file(1,n) is opened for appending, again being
               created if(3,n) necessary.

               You can put a '+' in(1,8) front of the '>' or '<' to indicate that
               you want both read(2,n,1 builtins) and write(1,2) access(2,5) to the file(1,n); thus '+<' is
               almost always preferred for read(2,n,1 builtins)/write(1,2) updates--the '+>' mode
               would clobber the file(1,n) first.  You can't usually use either
               read-write mode for updating textfiles, since they have vari-
               able length records.  See the -i switch(1,n) in(1,8) perlrun for a better
               approach.  The file(1,n) is created with permissions of 0666 modi-
               fied by the process' "umask" value.

               These various prefixes correspond to the fopen(3) modes of 'r',
               'r+', 'w', 'w+', 'a', and 'a+'