#!/usr/bin/perl

use strict;
use warnings;

$thing = "bleh";
print "hello $thing $bleh\n";
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#!/usr/bin/perl

use strict;
use warnings;
use Perl::Critic;

my $file = shift;
my $critic = Perl::Critic->new();
my @violations = $critic->critique($file);

print "@violations\n";
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$ perl critic ;perl thing 
Global symbol "$thing" requires explicit package name at thing line 6.
Global symbol "$thing" requires explicit package name at thing line 8.
Global symbol "$bleh" requires explicit package name at thing line 8.
Execution of thing aborted due to compilation errors.
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What's the purpose of this 'critic' module anyhow?

It is an attempt to programmatically check code against the conventions described in the "Perl Best Practices" book:

http://search.cpan.org/~elliotjs/Perl-Critic-1.116/lib/Perl/Critic.pm#DESCRIPTION

Your small code sample has no violations using the default settings on Perl::Critic. However, you can turn up the severity, and start to get complaints. I am more familiar with the perlcritic command line tool:

$ perlcritic -1 critic
Code is not tidy at line 1, column 1.  See page 33 of PBP.  (Severity:
+ 1)
Use Emacs file variables to declare coding style at line 1, column 1. 
+ Emacs can read per-file settings.  (Severity: 2)
RCS keywords $Id$ not found at line 1, column 1.  See page 441 of PBP.
+  (Severity: 2)
RCS keywords $Revision$, $HeadURL$, $Date$ not found at line 1, column
+ 1.  See page 441 of PBP.  (Severity: 2)
RCS keywords $Revision$, $Source$, $Date$ not found at line 1, column 
+1.  See page 441 of PBP.  (Severity: 2)
Missing Perl version at line 1, column 1.  Add "use 5.006" or similar.
+  (Severity: 1)
No package-scoped "$VERSION" variable found at line 1, column 1.  See 
+page 404 of PBP.  (Severity: 2)
Return value of flagged function ignored - print at line 11, column 1.
+  See pages 208,278 of PBP.  (Severity: 1)
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Your results may vary depending on the version of Perl::Critic (I also have additional policies loaded on my system).

UPDATE: Why didn't you pass a filename on the command line to your critic program? $file has not been assigned a value.

Also, to set the severity in your critic program:

my $critic = Perl::Critic->new(-severity=>1);
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