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strict(3) - strict - Perl pragma to restrict unsafe constructs - man 3 strict

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strict(3)              Perl Programmers Reference Guide              strict(3)



NAME
       strict - Perl pragma to restrict unsafe constructs

SYNOPSIS
           use strict;

           use strict "vars";
           use strict "refs";
           use strict "subs";

           use strict;
           no strict "vars";

DESCRIPTION
       If no import list is supplied, all possible restrictions are assumed.
       (This is the safest mode to operate in(1,8), but is sometimes too strict for
       casual programming.)  Currently, there are three possible things to be
       strict about:  "subs", "vars", and "refs".

       "strict refs"
             This generates a runtime error(8,n) if(3,n) you use symbolic references
             (see perlref).

                 use strict 'refs';
                 $ref = \$foo;
                 print $$ref;        # ok
                 $ref = "foo";
                 print $$ref;        # runtime error(8,n); normally ok
                 $file(1,n) = "STDOUT";
                 print $file(1,n) "Hi!";  # error(8,n); note: no comma after $file(1,n)

             There is one exception to this rule:

                 $bar = \&{'foo'};
                 &$bar;

             is allowed so that "goto &$AUTOLOAD" would not break under stric-
             ture.

       "strict vars"
             This generates a compile-time error(8,n) if(3,n) you access(2,5) a variable that
             wasn't declared via "our" or "use vars", localized via "my()", or
             wasn't fully qualified.  Because this is to avoid variable sui-
             cide problems and subtle dynamic scoping issues, a merely local()
             variable isn't good enough.  See "my" in(1,8) perlfunc and "local" in(1,8)
             perlfunc.

                 use strict 'vars';
                 $X::foo = 1;         # ok, fully qualified
                 my $foo = 10;        # ok, my() var
                 local $foo = 9;      # blows up

                 package Cinna;
                 our $bar;                   # Declares $bar in(1,8) current package
                 $bar = 'HgS';               # ok, global declared via pragma

             The local() generated a compile-time error(8,n) because you just
             touched a global name without fully qualifying it.

             Because of their special use by sort(1,3)(), the variables $a and $b
             are exempted from this check.

       "strict subs"
             This disables the poetry optimization, generating a compile-time
             error(8,n) if(3,n) you try to use a bareword identifier that's not a sub-
             routine, unless it is a simple identifier (no colons) and that it
             appears in(1,8) curly braces or on the left hand side of the "=>" sym-
             bol.

                 use strict 'subs';
                 $SIG{PIPE} = Plumber;       # blows up
                 $SIG{PIPE} = "Plumber";     # just fine: quoted string(3,n) is always ok
                 $SIG{PIPE} = \&Plumber;     # preferred form

       See "Pragmatic Modules" in(1,8) perlmodlib.

HISTORY
       "strict 'subs'", with Perl 5.6.1, erroneously permitted to use an
       unquoted compound identifier (e.g. "Foo::Bar") as a hash key (before
       "=>" or inside curlies), but without forcing it always to a literal
       string.

       Starting with Perl 5.8.1 strict is strict about its restrictions: if(3,n)
       unknown restrictions are used, the strict pragma will abort(3,7) with

           Unknown 'strict' tag(s) '...'



perl v5.8.5                       2001-09-21                         strict(3)

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