Perl

Perl Development Skill

Assist with all aspects of Perl development including creating files, writing code, running scripts, debugging, and testing.

Creating New Files

When creating a new Perl script (.pl) or module (.pm), always include the file header from CLAUDE.md using the Perl template. Every script must begin with:

#!/usr/bin/env perl
use strict;
use warnings;
use v5.36;

For modules, use the standard package structure:

package MyModule;
use strict;
use warnings;
use v5.36;

# module code here

1;

Running and Testing

• Run scripts with: perl -w <script.pl>
• Check syntax without executing: perl -c <script.pl>
• Run tests with: prove -v or perl -Ilib t/*.t
• Use perl -d <script.pl> information to help debug issues when the user asks

Code Quality

• Always use strict and use warnings
• Prefer modern Perl idioms (v5.36+ features like use v5.36 which enables strict, signatures, etc.)
• Use descriptive variable names following snake_case convention
• Use Perl's built-in documentation: check perldoc for module usage
• Prefer core modules over external dependencies when practical
• Use three-argument open with lexical filehandles
• Handle errors explicitly (open my $fh, '<', $file or die "Cannot open $file: $!")

Debugging

Built-in Perl debugging

• Add use Data::Dumper for inspecting complex data structures
• Use warn for debug output to STDERR
• Check for common issues: missing semicolons, incorrect sigils, scope problems
• Run perl -MO=Deparse <script.pl> to see how Perl interprets the code

Perl debugger (perl -d)

• Launch with: perl -d <script.pl>
• Key commands:
  • n (next line), s (step into), c (continue)
  • b <line> (set breakpoint), B <line> (delete breakpoint)
  • p <expr> (print expression), x <expr> (dump structure)
  • l (list source), T (stack backtrace)
  • w <expr> (watch expression), R (restart)
  • q (quit)
• Use perl -d -e 0 for an interactive Perl shell

Perl::Critic (static analysis)

• Enforces coding standards based on Perl Best Practices
• Run with: perlcritic <script.pl>
• Severity levels 1 (most strict) to 5 (least strict): perlcritic --severity 3 <script.pl>
• Use a .perlcriticrc file for project-specific policies
• Disable specific policies inline: ## no critic (PolicyName)
• Install with: cpanm Perl::Critic

Perl::Tidy (code formatter)

• Reformats Perl code to a consistent style
• Run with: perltidy <script.pl> (creates <script.pl>.tdy)
• In-place formatting: perltidy -b <script.pl>
• Use a .perltidyrc file for project-specific settings
• Install with: cpanm Perl::Tidy

Test::More and prove (testing framework)

• Perl's standard testing framework
• Run tests with: prove -v or prove -v -r t/
• Run a single test: prove -v t/specific_test.t
• Test file structure:

  use Test::More;
  
  is(my_function(1, 2), 3, 'addition works');
  ok(defined $result, 'result is defined');
  like($string, qr/pattern/, 'string matches pattern');
  is_deeply(\@got, \@expected, 'arrays match');
  
  done_testing();
  

• Additional test modules:
  • Test::Exception -- test that code dies/lives as expected
  • Test::Warn -- test warning output
  • Test::Deep -- flexible deep structure comparison
  • Test::MockObject -- mock objects for unit testing

CPAN Modules

• Install modules with: cpanm <Module::Name>
• Check if a module is installed: perl -M<Module::Name> -e1
• Prefer well-maintained, widely-used modules

Argument Handling

• If $ARGUMENTS is a filename ending in .pl or .pm, work with that file
• If $ARGUMENTS is "new ", scaffold a new file with proper headers
• If $ARGUMENTS is "run ", execute the script and report output
• If $ARGUMENTS is "test", run the project's test suite
• Otherwise, treat $ARGUMENTS as a general Perl development request