(R)?ex the friendly automation framework



The Rex-1.13.0 release is now available on CPAN. It adds on_no_change hooks for file management commands to trigger further actions when files are left unchanged. Upgrade is recommended for all users.


The Rex-1.12.2 release is now available on CPAN. It fixes various regressions, as well as bugs around file management. Upgrade is highly recommended for all users.


The Rex-1.12.1 release is now available on CPAN. It adds documentation for feature flags, and fixes a release packaging issue.


The Rex-1.12.0 release is now available on CPAN. It adds support for local rsync operations, improves tab completion for Bash and Zsh, and fixes related bugs. It also discontinues support for running Rex on Windows 7, Windows Server 2008 R2, and older versions since both mainstream and extended support has already ended for these products.

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Thanks to the support from their amazing team, Rex is now listed on StackShare.



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» Home » Docs » Guides » Just enough Perl for Rex

Just enough Perl for Rex

Perl is a scripting language designed to keep easy things easy, and make hard things possible. In this tutorial you will learn just enough Perl to write your own Rex tasks.

If you have suggestions or wishes, tell us on IRC, or just send a pull request against the GitHub repository.


Scalar variables

Scalars can contain single items, like strings, numbers, objects or references.

my $name  = 'John';     # this is a string
my $age   = 28;         # this is a number (integer)
my $float = 28.5;       # also a number, but a float
my $car   = Car->new(); # this is an object from the class Car

Array variables

Arrays are lists of scalars. Like a grocery list.

my @names  = ( 'John', 'Fred', 'Charley' );
my @to_buy = qw( Cheese Butter Salt );     # qw() quotes the words

To access an array element you have to use its index, which starts at zero:

say 'First name is: ' . $names[0];
say 'Last name is: ' . $name[2];
say 'Also the last name: ' . $name[-1];

Split a string into an array:

my $string = 'John,Fred,Charley';
my @names  = split( /,/, $string );

Join the items of an array into a string:

my @names  = qw( John Fred Charley );
my $string = join( ',', @names );    # -> John,Fred,Charley

If you want to iterate over an array, do it like this:

for my $name (@names) {
    say "Current name: $name"; # double quotes make variables interpolated

Hash variables

Hashes are like arrays, but with named indexes, called keys.

my %person = (
    name => 'John',
    age  => 28,    # good practice to keep a trailing comma

To access a hash element you have to use its key:

say 'Name: ' . $person{'name'};
say 'Age: ' . $person{age}; # perl can autoquote simple key names for you

If you want to iterate over a hash, do it like this:

for my $key ( keys %person ) {
    say "key: $key -> value: " . $person{$key};

But remember an important note: hashes are always unsorted.

Conditional statements

if ( $name eq 'John' ) {
    say 'Hello, my name is John!';
else {
    say 'Well, my name is not John...';

if ( $name ne 'John' ) {
    say 'Well, my name is not John...';
else {
    say 'Hello, my name is John!';

if ( $age < 30 ) {
    say 'I am younger than 30.';
elsif ( $age >= 30 && $age <= 50 ) {
    say 'Well, I am between 30 and 50.';
else {
    say 'I am older than 50.';


for my $num ( 1 .. 5 ) {
    say "> $num";

# looping over an array
for my $item (@array) {
    say "> $item";

Regular expressions

my $name = 'John';

if ( $name =~ m/john/ ) { # will _not_ match, because the 'J' in $name is uppercase

if ( $name =~ m/john/i ) { # _will_ match, because we use the 'i' modifier for case-insensitive matching

$name =~ s/john/Fred/i;    # this will replace the first match of 'john' (regardless of its case) with 'Fred'
$name =~ s/john/Fred/ig;   # this will replace all matches of 'john' (regardless of its case) with 'Fred'


sub my_function { # define the subroutine called 'my_function'

sub my_function2 { # @_ contains the parameters passed to the subroutine
    my ( $param1, $param2 ) = @_;

my_function();     # call the function 'my_function'
my_function;       # also calls 'my_function', but harder to read due to missing parentheses
&my_function;      # also calls 'my_function', but with a deprecated old notation

my_function2( 'john', 28 ); # call 'my_function2' with 2 parameters
my_function2 'john', 28;    # does the same, but harder to read due to missing parentheses

Useful helpers

Dump the content of a scalar, array or hash:

use Data::Dumper;
say Dumper($scalar);
say Dumper(@array);
say Dumper(%hash);

More documentation

If you want to learn more Perl you can find a great online tutorial on Perl Maven.

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