Modern Perl Development Patterns Idiomatic Perl 5.36+ patterns and best practices for building robust, maintainable applications. When to Activate Writing new Perl code or modules Reviewing Perl code for idiom compliance Refactoring legacy Perl to modern standards Designing Perl module architecture Migrating pre-5.36 code to modern Perl How It Works Apply these patterns as a bias toward modern Perl 5.36+ defaults: signatures, explicit modules, focused error handling, and testable boundaries. The examples below are meant to be copied as starting points, then tightened for the actual app, dependency stack, and deployment model in front of you. Core Principles 1. Use v5.36 Pragma A single use v5.36 replaces the old boilerplate and enables strict, warnings, and subroutine signatures.
Good: Modern preamble
use v5.36 ; sub greet ( $name ) { say "Hello, $name!" ; }
Bad: Legacy boilerplate
use strict ; use warnings ; use feature 'say' , 'signatures' ; no warnings 'experimental::signatures' ; sub greet { my ( $name ) = @_ ; say "Hello, $name!" ; } 2. Subroutine Signatures Use signatures for clarity and automatic arity checking. use v5.36 ;
Good: Signatures with defaults
sub connect_db ( $host , $port = 5432 , $timeout = 30 ) {
$host is required, others have defaults
return DBI -> connect ( "dbi:Pg:host=$host;port=$port" , undef , undef , { RaiseError => 1 , PrintError => 0 , } ) ; }
Good: Slurpy parameter for variable args
sub log_message ( $level , @details ) { say "[$level] " . join ( ' ' , @details ) ; }
Bad: Manual argument unpacking
sub connect_db { my ( $host , $port , $timeout ) = @_ ; $port //= 5432 ; $timeout //= 30 ;
...
} 3. Context Sensitivity Understand scalar vs list context — a core Perl concept. use v5.36 ; my @items = ( 1 , 2 , 3 , 4 , 5 ) ; my @copy = @items ;
List context: all elements
my $count = @items ;
Scalar context: count (5)
say "Items: " . scalar @items ;
Force scalar context
- Postfix Dereferencing Use postfix dereference syntax for readability with nested structures. use v5.36 ; my $data = { users => [ { name => 'Alice' , roles => [ 'admin' , 'user' ] } , { name => 'Bob' , roles => [ 'user' ] } , ] , } ;
Good: Postfix dereferencing
my @users = $data -> { users } -> @ ; my @roles = $data -> { users } [ 0 ] { roles } -> @ ; my %first = $data -> { users } [ 0 ] -> %* ;
Bad: Circumfix dereferencing (harder to read in chains)
my @users = @ { $data -> { users } } ; my @roles = @ { $data -> { users } [ 0 ] { roles } } ; 5. The isa Operator (5.32+) Infix type-check — replaces blessed($o) && $o->isa('X') . use v5.36 ; if ( $obj isa 'My::Class' ) { $obj -> do_something } Error Handling eval/die Pattern use v5.36 ; sub parse_config ( $path ) { my $content = eval { path ( $path ) -> slurp_utf8 } ; die "Config error: $@" if $@ ; return decode_json ( $content ) ; } Try::Tiny (Reliable Exception Handling) use v5.36 ; use Try : : Tiny ; sub fetch_user ( $id ) { my $user = try { $db -> resultset ( 'User' ) -> find ( $id ) // die "User $id not found\n" ; } catch { warn "Failed to fetch user $id: $_" ; undef ; } ; return $user ; } Native try/catch (5.40+) use v5.40 ; sub divide ( $x , $y ) { try { die "Division by zero" if $y == 0 ; return $x / $ y; } catch ($e) { warn "Error: $e"; return; } } Modern OO with Moo Prefer Moo for lightweight, modern OO. Use Moose only when its metaprotocol is needed.
Good: Moo class
package User ; use Moo ; use Types : : Standard qw(Str Int ArrayRef) ; use namespace : : autoclean ; has name => ( is => 'ro' , isa => Str , required => 1 ) ; has email => ( is => 'ro' , isa => Str , required => 1 ) ; has age => ( is => 'ro' , isa => Int , default => sub { 0 } ) ; has roles => ( is => 'ro' , isa => ArrayRef [ Str ] , default => sub { [ ] } ) ; sub is_admin ( $self ) { return grep { $_ eq 'admin' } $self -> roles -> @* ; } sub greet ( $self ) { return "Hello, I'm " . $self -> name ; } 1 ;
Usage
my $user = User -> new ( name => 'Alice' , email => 'alice@example.com' , roles => [ 'admin' , 'user' ] , ) ;
Bad: Blessed hashref (no validation, no accessors)
package User ; sub new { my ( $class , %args ) = @ ; return bless \ %args , $class ; } sub name { return $ [ 0 ] -> { name } } 1 ; Moo Roles package Role : : Serializable ; use Moo : : Role ; use JSON : : MaybeXS qw(encode_json) ; requires 'TO_HASH' ; sub to_json ( $self ) { encode_json ( $self -> TO_HASH ) } 1 ; package User ; use Moo ; with 'Role::Serializable' ; has name => ( is => 'ro' , required => 1 ) ; has email => ( is => 'ro' , required => 1 ) ; sub TO_HASH ( $self ) { { name => $self -> name , email => $self -> email } } 1 ; Native class Keyword (5.38+, Corinna) use v5.38 ; use feature 'class' ; no warnings 'experimental::class' ; class Point { field $x : param ; field $y : param ; method magnitude ( ) { sqrt ( $x * 2 + $y * 2 ) } } my $p = Point -> new ( x => 3 , y => 4 ) ; say $p -> magnitude ;
5
Regular Expressions Named Captures and /x Flag use v5.36 ;
Good: Named captures with /x for readability
my
$log_re
=
qr
{
^
(
?
Bad: Positional captures (hard to maintain)
if ($line =~ /^(\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2})\s+[(\w+)]\s + ( . + ) $/ ) { say "Time: $1, Level: $2" ; } Precompiled Patterns use v5.36 ;
Good: Compile once, use many
my $email_re = qr/^[A-Za-z0-9.%+-]+\@[A-Za-z0-9.-]+.[A-Za-z]{2,}$/ ; sub validate_emails ( @emails ) { return grep { $ =~ $email_re } @emails ; } Data Structures References and Safe Deep Access use v5.36 ;
Hash and array references
my $config = { database => { host => 'localhost' , port => 5432 , options => [ 'utf8' , 'sslmode=require' ] , } , } ;
Safe deep access (returns undef if any level missing)
my $port = $config -> { database } { port } ;
5432
my $missing = $config -> { cache } { host } ;
undef, no error
Hash slices
my %subset ; @subset { qw(host port) } = @ { $config -> { database } } { qw(host port) } ;
Array slices
my @first_two = $config -> { database } { options } -> @[ 0 , 1 ] ;
Multi-variable for loop (experimental in 5.36, stable in 5.40)
use feature 'for_list' ; no warnings 'experimental::for_list' ; for my ( $key , $val ) ( %$config ) { say "$key => $val" ; } File I/O Three-Argument Open use v5.36 ;
Good: Three-arg open with autodie (core module, eliminates 'or die')
use autodie ; sub read_file ( $path ) { open my $fh , '<:encoding(UTF-8)' , $path ; local $/ ; my $content = < $fh
; close $fh ; return $content ; }
Bad: Two-arg open (shell injection risk, see perl-security)
open FH , $path ;
NEVER do this
open FH , "< $path" ;
Still bad — user data in mode string
Path::Tiny for File Operations use v5.36 ; use Path : : Tiny ; my $file = path ( 'config' , 'app.json' ) ; my $content = $file -> slurp_utf8 ; $file -> spew_utf8 ( $new_content ) ;
Iterate directory
for my $child ( path ( 'src' ) -> children ( qr/.pl$/ ) ) { say $child -> basename ; } Module Organization Standard Project Layout MyApp/ ├── lib/ │ └── MyApp/ │ ├── App.pm # Main module │ ├── Config.pm # Configuration │ ├── DB.pm # Database layer │ └── Util.pm # Utilities ├── bin/ │ └── myapp # Entry-point script ├── t/ │ ├── 00-load.t # Compilation tests │ ├── unit/ # Unit tests │ └── integration/ # Integration tests ├── cpanfile # Dependencies ├── Makefile.PL # Build system └── .perlcriticrc # Linting config Exporter Patterns package MyApp : : Util ; use v5.36 ; use Exporter 'import' ; our @EXPORT_OK = qw(trim) ; our %EXPORT_TAGS = ( all => \ @EXPORT_OK ) ; sub trim ( $str ) { $str =~ s/^\s+|\s+$//gr } 1 ; Tooling perltidy Configuration (.perltidyrc) -i=4 # 4-space indent -l=100 # 100-char line length -ci=4 # continuation indent -ce # cuddled else -bar # opening brace on same line -nolq # don't outdent long quoted strings perlcritic Configuration (.perlcriticrc) severity = 3 theme = core + pbp + security [ InputOutput::RequireCheckedSyscalls ] functions = :builtins exclude_functions = say print [ Subroutines::ProhibitExplicitReturnUndef ] severity = 4 [ ValuesAndExpressions::ProhibitMagicNumbers ] allowed_values = 0 1 2 -1 Dependency Management (cpanfile + carton) cpanm App::cpanminus Carton
Install tools
carton install
Install deps from cpanfile
carton exec -- perl bin/myapp
Run with local deps
cpanfile
requires 'Moo' , '>= 2.005' ; requires 'Path::Tiny' ; requires 'JSON::MaybeXS' ; requires 'Try::Tiny' ; on test => sub { requires 'Test2::V0' ; requires 'Test::MockModule' ; } ; Quick Reference: Modern Perl Idioms Legacy Pattern Modern Replacement use strict; use warnings; use v5.36; my ($x, $y) = @_; sub foo($x, $y) { ... } @{ $ref } $ref->@ %{ $ref } $ref->% open FH, "< $file" open my $fh, '<:encoding(UTF-8)', $file blessed hashref Moo class with types $1, $2, $3 $+{name} (named captures) eval { }; if ($@) Try::Tiny or native try/catch (5.40+) BEGIN { require Exporter; } use Exporter 'import'; Manual file ops Path::Tiny blessed($o) && $o->isa('X') $o isa 'X' (5.32+) builtin::true / false use builtin 'true', 'false'; (5.36+, experimental) Anti-Patterns
1. Two-arg open (security risk)
open FH , $filename ;
NEVER
2. Indirect object syntax (ambiguous parsing)
my $obj = new Foo ( bar => 1 ) ;
Bad
my $obj = Foo -> new ( bar => 1 ) ;
Good
3. Excessive reliance on $_
map { process ( $ ) } grep { validate ( $ ) } @items ;
Hard to follow
my @valid = grep { validate ( $_ ) } @items ;
Better: break it up
my @results = map { process ( $_ ) } @valid ;
4. Disabling strict refs
no strict 'refs' ;
Almost always wrong
$ { "My::Package::$var" } = $value ;
Use a hash instead
5. Global variables as configuration
our $TIMEOUT = 30 ;
Bad: mutable global
use constant TIMEOUT => 30 ;
Better: constant
Best: Moo attribute with default
6. String eval for module loading
eval "require $module" ;
Bad: code injection risk
eval "use $module" ;
Bad
use Module : : Runtime 'require_module' ;
Good: safe module loading
- require_module
- (
- $module
- )
- ;
- Remember
- Modern Perl is clean, readable, and safe. Let use v5.36 handle the boilerplate, use Moo for objects, and prefer CPAN's battle-tested modules over hand-rolled solutions.