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

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

NNAAMMEE #

 strict - Perl pragma to restrict unsafe constructs

SSYYNNOOPPSSIISS #

     use strict;

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

     use strict;
     no strict "vars";

DDEESSCCRRIIPPTTIIOONN #

 The "strict" pragma disables certain Perl expressions that could behave
 unexpectedly or are difficult to debug, turning them into errors. The
 effect of this pragma is limited to the current file or scope block.

 If no import list is supplied, all possible restrictions are assumed.
 (This is the safest mode to operate in, 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 if you use symbolic references (see
       perlref).

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

       There is one exception to this rule:

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

       is allowed so that "goto &$AUTOLOAD" would not break under
       stricture.

 "strict vars"
       This generates a compile-time error if you access a variable that
       was neither explicitly declared (using any of "my", "our", "state",
       or "use vars") nor fully qualified.  (Because this is to avoid
       variable suicide problems and subtle dynamic scoping issues, a
       merely "local" variable isn't good enough.)  See "my" in perlfunc,
       "our" in perlfunc, "state" in perlfunc, "local" in perlfunc, and
       vars.

           use strict 'vars';
           $X::foo = 1;         # ok, fully qualified
           my $foo = 10;        # ok, my() var
           local $baz = 9;      # blows up, $baz not declared before

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

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

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

 "strict subs"
       This disables the poetry optimization, generating a compile-time
       error if you try to use a bareword identifier that's not a
       subroutine, unless it is a simple identifier (no colons) and that
       it appears in curly braces, on the left hand side of the "=>"
       symbol, or has the unary minus operator applied to it.

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

 See "Pragmatic Modules" in perlmodlib.

HHIISSTTOORRYY #

 "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
 unknown restrictions are used, the strict pragma will abort with

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

 As of version 1.04 (Perl 5.10), strict verifies that it is used as
 "strict" to avoid the dreaded Strict trap on case insensitive file
 systems.

perl v5.36.3 2023-02-15 strict(3p)