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Full Discussion: Perl strict
Top Forums Shell Programming and Scripting Perl strict Post 302276573 by buffoonix on Wednesday 14th of January 2009 05:42:27 AM
Old 01-14-2009
If you don't use the strict pragma in a Perl programme all the variables you define (or rather introduce) become implicitly package globals that appear in the symbol table.
At first glance this might tremendously ease the coding (for the novice) but this also is hugely error prone, especially to typos.
So if you inadvertently misspell a variable without strict the Perl compiler would silently declare a new package global without the faintest sign of warning, but this most of the times is pretty useless or even detrimental and will break your programme logic since you intended to refer to some previously declared and defined variable.
Instead when you use strict the Perl compiler will immediately abort compilation and issue an error message hinting at the reason and line which violated the syntax.
Besides, it is considered bad programming style to use global variables,
and one should almost always use lexically scoped variables (those declared by my)
Therefore, even the seasoned Perl programmer should always have the use strict; line at the beginning at their code, and that is one vital marker that indicates good Perl code.
 

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

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, 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 wasn't declared via "our" or "use vars", localized via "my()", or wasn't fully qualified. Because this is to avoid variable suicide problems and subtle dynamic scoping issues, a merely local() vari- able isn't good enough. See "my" in perlfunc and "local" in 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 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 subrou- tine, unless 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: bareword in curlies always ok $SIG{PIPE} = &Plumber; # preferred form See "Pragmatic Modules" in perlmodlib. perl v5.8.0 2002-06-01 strict(3pm)
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