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

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, 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 or on the left hand side of the "=>" symbol. use strict 'subs'; $SIG{PIPE} = Plumber; # blows up $SIG{PIPE} = "Plumber"; # just 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. perl v5.16.3 2013-03-04 strict(3pm)

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Symbol(3pm)						 Perl Programmers Reference Guide					       Symbol(3pm)

Symbol - manipulate Perl symbols and their names SYNOPSIS
use Symbol; $sym = gensym; open($sym, "filename"); $_ = <$sym>; # etc. ungensym $sym; # no effect # replace *FOO{IO} handle but not $FOO, %FOO, etc. *FOO = geniosym; print qualify("x"), " "; # "main::x" print qualify("x", "FOO"), " "; # "FOO::x" print qualify("BAR::x"), " "; # "BAR::x" print qualify("BAR::x", "FOO"), " "; # "BAR::x" print qualify("STDOUT", "FOO"), " "; # "main::STDOUT" (global) print qualify(*x), " "; # returns *x print qualify(*x, "FOO"), " "; # returns *x use strict refs; print { qualify_to_ref $fh } "foo! "; $ref = qualify_to_ref $name, $pkg; use Symbol qw(delete_package); delete_package('Foo::Bar'); print "deleted " unless exists $Foo::{'Bar::'}; DESCRIPTION
"Symbol::gensym" creates an anonymous glob and returns a reference to it. Such a glob reference can be used as a file or directory handle. For backward compatibility with older implementations that didn't support anonymous globs, "Symbol::ungensym" is also provided. But it doesn't do anything. "Symbol::geniosym" creates an anonymous IO handle. This can be assigned into an existing glob without affecting the non-IO portions of the glob. "Symbol::qualify" turns unqualified symbol names into qualified variable names (e.g. "myvar" -> "MyPackage::myvar"). If it is given a second parameter, "qualify" uses it as the default package; otherwise, it uses the package of its caller. Regardless, global variable names (e.g. "STDOUT", "ENV", "SIG") are always qualified with "main::". Qualification applies only to symbol names (strings). References are left unchanged under the assumption that they are glob references, which are qualified by their nature. "Symbol::qualify_to_ref" is just like "Symbol::qualify" except that it returns a glob ref rather than a symbol name, so you can use the result even if "use strict 'refs'" is in effect. "Symbol::delete_package" wipes out a whole package namespace. Note this routine is not exported by default--you may want to import it explicitly. BUGS
"Symbol::delete_package" is a bit too powerful. It undefines every symbol that lives in the specified package. Since perl, for performance reasons, does not perform a symbol table lookup each time a function is called or a global variable is accessed, some code that has already been loaded and that makes use of symbols in package "Foo" may stop working after you delete "Foo", even if you reload the "Foo" module afterwards. perl v5.16.3 2013-02-26 Symbol(3pm)
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