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grep(1) - egrep, fgrep, grep, egrep, fgrep, grep - print lines matching a pattern - man 1 grep

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GREP(1)                                                                GREP(1)



NAME
       grep, egrep, fgrep - print lines matching a pattern

SYNOPSIS
       grep [options] PATTERN [FILE...]
       grep [options] [-e PATTERN | -f FILE] [FILE...]

DESCRIPTION
       Grep  searches the named(5,8) input FILEs (or standard input if(3,n) no files are
       named(5,8), or the file(1,n) name - is given) for lines containing a match to the
       given PATTERN.  By default, grep prints the matching lines.

       In addition, two variant programs egrep and fgrep are available.  Egrep
       is the same as grep -E.  Fgrep is the same as grep -F.

OPTIONS
       -A NUM, --after-context=NUM
              Print NUM  lines  of  trailing  context  after  matching  lines.
              Places  a  line  containing  --  between  contiguous  groups  of
              matches.

       -a, --text
              Process a binary file(1,n) as if(3,n) it were text; this is equivalent  to
              the --binary-files=text option.

       -B NUM, --before-context=NUM
              Print  NUM  lines  of  leading  context  before  matching lines.
              Places  a  line  containing  --  between  contiguous  groups  of
              matches.

       -C NUM, --context=NUM
              Print  NUM lines of output context.  Places a line containing --
              between contiguous groups of matches.

       -b, --byte-offset
              Print the byte offset within the input file(1,n) before each line  of
              output.

       --binary-files=TYPE
              If the first few bytes of a file(1,n) indicate that the file(1,n) contains
              binary data, assume that the file(1,n) is of type TYPE.  By  default,
              TYPE is binary, and grep normally outputs either a one-line mes-
              sage saying that a binary file(1,n) matches, or no message  if(3,n)  there
              is  no  match.   If  TYPE  is without-match, grep assumes that a
              binary file(1,n) does not match; this is equivalent to the -I option.
              If  TYPE  is  text,  grep  processes a binary file(1,n) as if(3,n) it were
              text; this is  equivalent  to  the  -a  option.   Warning:  grep
              --binary-files=text  might output binary garbage, which can have
              nasty side effects if(3,n) the output is a terminal and if(3,n) the termi-
              nal driver interprets some of it as commands.

       --colour[=WHEN], --color[=WHEN]
              Surround  the matching string(3,n) with the marker find in(1,8) GREP_COLOR
              environment variable. WHEN may be `never', `always', or `auto(5,8)'

       -c, --count
              Suppress normal output; instead print a count of matching  lines
              for  each  input  file.  With the -v, --invert-match option (see
              below), count non-matching lines.

       -D ACTION, --devices=ACTION
              If an input file(1,n) is a device, FIFO  or  socket(2,7,n),  use  ACTION  to
              process  it.   By  default,  ACTION  is  read(2,n,1 builtins),  which means that
              devices are read(2,n,1 builtins) just as if(3,n) they were ordinary files.  If ACTION
              is skip, devices are silently skipped.

       -d ACTION, --directories=ACTION
              If  an  input file(1,n) is a directory, use ACTION to process it.  By
              default, ACTION is read(2,n,1 builtins), which means that directories  are  read(2,n,1 builtins)
              just  as if(3,n) they were ordinary files.  If ACTION is skip, direc-
              tories are silently skipped.  If ACTION is recurse,  grep  reads
              all  files under each directory, recursively; this is equivalent
              to the -r option.

       -E, --extended-regexp
              Interpret PATTERN as an extended regular expression (see below).

       -e PATTERN, --regexp=PATTERN
              Use PATTERN as the pattern; useful to protect patterns beginning
              with -.

       -F, --fixed-strings
              Interpret PATTERN as a list of fixed strings, separated by  new-
              lines,  any of which is to be matched.  -P, --perl-regexp Inter-
              pret PATTERN as a Perl regular expression.

       -f FILE, --file=FILE
              Obtain patterns from FILE, one per line.  The  empty  file(1,n)  con-
              tains zero patterns, and therefore matches nothing.

       -G, --basic-regexp
              Interpret  PATTERN  as  a  basic regular expression (see below).
              This is the default.

       -H, --with-filename
              Print the filename for each match.

       -h, --no-filename
              Suppress the prefixing of  filenames  on  output  when  multiple
              files are searched.

       --help Output a brief help message.

       -I     Process  a  binary  file(1,n) as if(3,n) it did not contain matching data;
              this is equivalent to the --binary-files=without-match option.

       -i, --ignore-case
              Ignore case distinctions in(1,8)  both  the  PATTERN  and  the  input
              files.

       -L, --files-without-match
              Suppress  normal  output;  instead  print the name of each input
              file(1,n) from which no output would normally have been printed.  The
              scanning will stop on the first match.

       -l, --files-with-matches
              Suppress  normal  output;  instead  print the name of each input
              file(1,n) from which output would normally have  been  printed.   The
              scanning will stop on the first match.

       -m NUM, --max-count=NUM
              Stop  reading  a file(1,n) after NUM matching lines.  If the input is
              standard input from a regular file(1,n), and NUM matching  lines  are
              output,  grep  ensures  that the standard input is positioned to
              just after the last matching line before exiting, regardless  of
              the  presence of trailing context lines.  This enables a calling
              process to resume a search.  When grep stops after NUM  matching
              lines,  it  outputs  any trailing context lines.  When the -c or
              --count option is also  used,  grep  does  not  output  a  count
              greater  than NUM.  When the -v or --invert-match option is also
              used, grep stops after outputting NUM non-matching lines.

       --mmap If possible, use the mmap(2) system call to read(2,n,1 builtins) input,  instead
              of  the default read(2,n,1 builtins)(2) system call.  In some situations, --mmap
              yields better performance.  However, --mmap can cause  undefined
              behavior  (including  core dumps) if(3,n) an input file(1,n) shrinks while
              grep is operating, or if(3,n) an I/O error(8,n) occurs.

       -n, --line-number
              Prefix each line of output with the line number within its input
              file.

       -o, --only-matching
              Show only the part of a matching line that matches PATTERN.

       --label=LABEL
              Displays input actually coming from standard input as input com-
              ing from file(1,n) LABEL.  This is especially useful for  tools  like
              zgrep, e.g.  gzip -cd foo.gz |grep --label=foo something

       --line-buffering
              Use line buffering, it can be a performance penality.

       -q, --quiet, --silent
              Quiet;  do  not write(1,2) anything to standard output.  Exit immedi-
              ately with zero status if(3,n) any match is found, even if(3,n)  an  error(8,n)
              was detected.  Also see the -s or --no-messages option.

       -R, -r, --recursive
              Read all files under each directory, recursively; this is equiv-
              alent to the -d recurse option.

         --include=PATTERN
              Recurse in(1,8) directories only searching file(1,n) matching PATTERN.

         --exclude=PATTERN
              Recurse in(1,8) directories skip file(1,n) matching PATTERN.

       -s, --no-messages
              Suppress error(8,n) messages about nonexistent or  unreadable  files.
              Portability note: unlike GNU grep, traditional grep did not con-
              form to POSIX.2, because traditional grep lacked a -q option and
              its  -s option behaved like GNU grep's -q option.  Shell scripts
              intended to be portable to traditional grep should avoid both -q
              and -s and should redirect output to /dev/null instead.

       -U, --binary
              Treat  the  file(1,n)(s) as binary.  By default, under MS-DOS and MS-
              Windows, grep guesses the file(1,n) type by looking at  the  contents
              of  the first 32KB read(2,n,1 builtins) from the file.  If grep decides the file(1,n)
              is a text file(1,n), it strips the CR characters  from  the  original
              file(1,n)  contents  (to  make  regular expressions with ^ and $ work
              correctly).  Specifying -U overrules this guesswork, causing all
              files  to be read(2,n,1 builtins) and passed to the matching mechanism verbatim;
              if(3,n) the file(1,n) is a text file(1,n) with CR/LF pairs at the end  of  each
              line,  this  will  cause some regular expressions to fail.  This
              option has no effect on platforms other than MS-DOS and  MS-Win-
              dows.

       -u, --unix-byte-offsets
              Report  Unix-style  byte  offsets.   This  switch(1,n) causes grep to
              report byte offsets as if(3,n) the file(1,n) were  Unix-style  text  file(1,n),
              i.e. with CR characters stripped off.  This will produce results
              identical to running grep on a Unix machine.  This option has no
              effect  unless -b option is also used; it has no effect on plat-
              forms other than MS-DOS and MS-Windows.

       -V, --version
              Print the version(1,3,5) number of grep to standard error.   This  ver-
              sion(1,3,5) number should be included in(1,8) all bug reports (see below).

       -v, --invert-match
              Invert the sense of matching, to select(2,7,2 select_tut) non-matching lines.

       -w, --word-regexp
              Select  only  those  lines  containing  matches  that form whole
              words.  The test is that the matching substring must  either  be
              at  the  beginning  of  the line, or preceded by a non-word con-
              stituent character.  Similarly, it must be either at the end  of
              the line or followed by a non-word constituent character.  Word-
              constituent characters are letters, digits, and the  underscore.

       -x, --line-regexp
              Select only those matches that exactly match the whole line.

       -y     Obsolete synonym for -i.

       -Z, --null
              Output  a  zero  byte  (the  ASCII NUL character) instead of the
              character that normally follows a file(1,n) name.  For example,  grep
              -lZ  outputs  a  zero  byte  after each file(1,n) name instead of the
              usual newline.  This option makes the output  unambiguous,  even
              in(1,8) the presence of file(1,n) names containing unusual characters like
              newlines.  This option can  be  used  with  commands  like  find
              -print0,  perl  -0,  sort(1,3)  -z, and xargs -0 to process arbitrary
              file(1,n) names, even those that contain newline characters.

REGULAR EXPRESSIONS
       A regular expression is a pattern that  describes  a  set(7,n,1 builtins)  of  strings.
       Regular  expressions  are constructed analogously to arithmetic expres-
       sions, by using various operators to combine smaller expressions.

       Grep understands two different versions of regular  expression  syntax:
       "basic"  and "extended."  In GNU grep, there is no difference in(1,8) avail-
       able functionality using  either  syntax.   In  other  implementations,
       basic regular expressions are less(1,3) powerful.  The following description
       applies to extended regular expressions; differences for basic  regular
       expressions are summarized afterwards.

       The  fundamental building blocks are the regular expressions that match
       a single character.  Most characters, including all letters and digits,
       are  regular expressions that match themselves.  Any metacharacter with
       special meaning may be quoted by preceding it with a backslash.

       A bracket expression is a list of characters enclosed by [ and  ].   It
       matches  any  single  character in(1,8) that list; if(3,n) the first character of
       the list is the caret ^ then it matches any character not in(1,8) the  list.
       For  example,  the  regular  expression [0123456789] matches any single
       digit.

       Within a bracket expression, a range expression consists of two charac-
       ters separated by a hyphen.  It matches any single character that sorts
       between the two characters, inclusive,  using  the  locale(3,5,7)'s  collating
       sequence  and  character  set.   For  example, in(1,8) the default C locale(3,5,7),
       [a-d] is equivalent to [abcd].  Many locales sort(1,3) characters in(1,8) dictio-
       nary  order,  and in(1,8) these locales [a-d] is typically not equivalent to
       [abcd]; it might be equivalent to [aBbCcDd], for  example.   To  obtain
       the  traditional interpretation of bracket expressions, you can use the
       C locale(3,5,7) by setting the LC_ALL environment variable to the value C.

       Finally, certain named(5,8) classes  of  characters  are  predefined  within
       bracket expressions, as follows.  Their names are self explanatory, and
       they  are  [:alnum:],  [:alpha:],  [:cntrl:],   [:digit:],   [:graph:],
       [:lower:],  [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:].
       For example, [[:alnum:]] means  [0-9A-Za-z],  except  the  latter  form
       depends upon the C locale(3,5,7) and the ASCII character encoding(3,n), whereas the
       former is independent of locale(3,5,7) and  character  set.   (Note  that  the
       brackets  in(1,8) these class names are part of the symbolic names, and must
       be included in(1,8) addition to the brackets delimiting the  bracket  list.)
       Most  metacharacters  lose  their  special  meaning  inside  lists.  To
       include a literal ] place it first in(1,8) the list.  Similarly, to  include
       a literal ^ place it anywhere but first.  Finally, to include a literal
       - place it last.

       The period .  matches any single character.  The symbol \w is a synonym
       for [[:alnum:]] and \W is a synonym for [^[:alnum]].

       The  caret ^ and the dollar sign $ are metacharacters that respectively
       match the empty string(3,n) at the beginning and end of a line.  The symbols
       \<  and \> respectively match the empty string(3,n) at the beginning and end
       of a word.  The symbol \b matches the empty string(3,n) at  the  edge  of  a
       word,  and \B matches the empty string(3,n) provided it's not at the edge of
       a word.

       A regular expression may be followed by one of several repetition oper-
       ators:
       ?      The preceding item is optional and matched at most once.
       *      The preceding item will be matched zero or more times.
       +      The preceding item will be matched one or more times.
       {n}    The preceding item is matched exactly n times.
       {n,}   The preceding item is matched n or more times.
       {n,m}  The  preceding  item  is  matched at least n times, but not more
              than m times.

       Two regular expressions may  be  concatenated;  the  resulting  regular
       expression  matches  any  string(3,n) formed by concatenating two substrings
       that respectively match the concatenated subexpressions.

       Two regular expressions may be joined by  the  infix  operator  |;  the
       resulting  regular expression matches any string(3,n) matching either subex-
       pression.

       Repetition takes precedence over concatenation,  which  in(1,8)  turn  takes
       precedence  over alternation.  A whole subexpression may be enclosed in(1,8)
       parentheses to override these precedence rules.

       The backreference \n, where n is a single digit, matches the  substring
       previously  matched by the nth parenthesized subexpression of the regu-
       lar expression.

       In basic regular expressions the metacharacters ?, +, {, |,  (,  and  )
       lose  their  special  meaning; instead use the backslashed versions \?,
       \+, \{, \|, \(, and \).

       Traditional egrep did not support the { metacharacter, and  some  egrep
       implementations  support \{ instead, so portable scripts should avoid {
       in(1,8) egrep patterns and should use [{] to match a literal {.

       GNU egrep attempts to support traditional usage by assuming that  {  is
       not  special if(3,n) it would be the start of an invalid interval specifica-
       tion.  For example, the shell command egrep '{1' searches for the  two-
       character  string(3,n) {1 instead of reporting a syntax error(8,n) in(1,8) the regular
       expression.  POSIX.2 allows this behavior as an extension, but portable
       scripts should avoid it.

ENVIRONMENT VARIABLES
       Grep's behavior is affected by the following environment variables.

       A  locale(3,5,7)  LC_foo is specified by examining the three environment vari-
       ables LC_ALL, LC_foo, LANG, in(1,8) that order.  The first  of  these  vari-
       ables  that is set(7,n,1 builtins) specifies the locale.  For example, if(3,n) LC_ALL is not
       set(7,n,1 builtins), but LC_MESSAGES is set(7,n,1 builtins) to pt_BR, then Brazilian Portuguese is used
       for  the  LC_MESSAGES  locale.   The  C locale(3,5,7) is used if(3,n) none of these
       environment variables  are  set(7,n,1 builtins),  or  if(3,n)  the  locale(3,5,7)  catalog  is  not
       installed,  or  if(3,n) grep was not compiled with national language support
       (NLS).

       GREP_OPTIONS
              This variable specifies default options to be placed in(1,8) front of
              any   explicit   options.    For  example,  if(3,n)  GREP_OPTIONS  is
              '--binary-files=without-match --directories=skip', grep  behaves
              as  if(3,n) the two options --binary-files=without-match and --direc-
              tories=skip had been  specified  before  any  explicit  options.
              Option  specifications are separated by whitespace.  A backslash
              escapes the next character, so it can  be  used  to  specify  an
              option containing whitespace or a backslash.

       GREP_COLOR
              Specifies the marker for highlighting.

       LC_ALL, LC_COLLATE, LANG
              These  variables specify the LC_COLLATE locale(3,5,7), which determines
              the collating sequence used to interpret range expressions  like
              [a-z].

       LC_ALL, LC_CTYPE, LANG
              These  variables  specify  the LC_CTYPE locale(3,5,7), which determines
              the type of characters, e.g., which characters are whitespace.

       LC_ALL, LC_MESSAGES, LANG
              These variables specify the LC_MESSAGES locale(3,5,7), which determines
              the  language that grep uses for messages.  The default C locale(3,5,7)
              uses American English messages.

       POSIXLY_CORRECT
              If set(7,n,1 builtins),  grep  behaves  as  POSIX.2  requires;  otherwise,  grep
              behaves  more  like  other  GNU programs.  POSIX.2 requires that
              options that follow file(1,n) names must be treated as file(1,n) names; by
              default,  such  options are permuted to the front of the operand
              list and are treated as options.  Also,  POSIX.2  requires  that
              unrecognized  options  be diagnosed as "illegal", but since they
              are not really against the law the default is to  diagnose  them
              as   "invalid".   POSIXLY_CORRECT  also  disables  _N_GNU_nonop-
              tion_argv_flags_, described below.

       _N_GNU_nonoption_argv_flags_
              (Here N is grep's numeric process ID.)  If the ith character  of
              this  environment variable's value is 1, do not consider the ith
              operand of grep to be an option, even if(3,n) it appears to  be  one.
              A  shell  can put this variable in(1,8) the environment for each com-
              mand it runs, specifying which operands are the results of  file(1,n)
              name  wildcard  expansion and therefore should not be treated as
              options.  This  behavior  is  available  only  with  the  GNU  C
              library, and only when POSIXLY_CORRECT is not set.

DIAGNOSTICS
       Normally, exit(3,n,1 builtins) status is 0 if(3,n) selected lines are found and 1 otherwise.
       But the exit(3,n,1 builtins) status is 2 if(3,n) an error(8,n) occurred, unless the -q or --quiet
       or --silent option is used and a selected line is found.

BUGS
       Email  bug  reports  to  bug-gnu-utils@gnu.org.  Be sure to include the
       word "grep" somewhere in(1,8) the "Subject:" field.

       Large repetition counts in(1,8) the {n,m} construct may cause  grep  to  use
       lots of memory.  In addition, certain other obscure regular expressions
       require exponential time(1,2,n) and space, and may cause grep to  run  out  of
       memory.

       Backreferences are very slow, and may require exponential time.



GNU Project                       2002/01/22                           GREP(1)

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