phpman > man > strict(3perl)

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

          Because of their special use by sort(), 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.

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 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.