(R)?ex Deployment & Configuration Management

News

2019-07-02
Deprecating official Rex packages

As part of our efforts to simplify maintenance around RexOps projects, we have decided to stop building Rex packages on our side. We recommend relying on OS packages maintained by the various distributions in their respective upstream repositories, or to install Rex from CPAN.

2019-06-09
Post-migration updates & clean-up

Over the course of the past weeks many clean-ups have been done, reaping the benefits provided by our new Statocles-based site:

2019-05-19
New site engine for rexify.org

After months of work on a new site backend, we reached the MVP today for our site to be switched over to a new engine: from now on, our site will be maintained using the static site generator Statocles.

Conferences

2016-06-21

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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, please post a comment, tell us in our #rex channel on freenode, or just send a pull request against the GitHub repository.

Variables

Scalar variables

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

my $name  = "John";     # this is a stringmy $age   = 28;         # this is a number (integer)my $float = 28.5;       # also a number, but a floatmy $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 Lemons Oranges Apples );

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

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

Split a string into an array:

my $string = "John,Fred,Carl,Lewis";
⁠my @names  = split( /,/, $string );

Join the items of an array into a string:

my @names  = ( "John", "Fred", "Carl", "Lewis" );
⁠my $string = join( ",", @names );                # -> John,Fred,Carl,Lewis

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

⁠for my $name (@names) {
⁠  say "Current name: $name";
⁠}

Hash variables

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

my %person = (
⁠  name => "John",
⁠  age  => 28,
⁠  city => "New York"
⁠);

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

⁠say "Name: " . $person{"name"};
⁠say "Age: " . $person{"age"};
⁠say "City: " . $person{"city"};

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 "Yes, my name is NOT John...";
⁠}
⁠else {
⁠  say "Hello, my name is John!";
⁠}
⁠
⁠if ( $age < 30 ) {
⁠  say "I'm younger than 30.";
⁠}
⁠elsif ( $age >= 30 && $age <= 50 ) {
⁠  say "Well, I'm between 30 and 50.";
⁠}
⁠else {
⁠  say "I'm older than 50.";
⁠}

Loops

for my $num ( 1 .. 5 ) {
⁠  say "> $num";
⁠}
⁠
⁠# looping over an arrayfor 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"

Functions

sub my_function { # define the function called "my_function"}
⁠
⁠sub my_function2 { # define the function called "my_function2"  my $param1 = $_[0]; # get the 1st parameter and save it in $param1  my $param2 = $_[1]; # get the 2nd parameter and save it in $param2  my $param3 = $_[2]; # get the 3rd parameter and save it in $param3}
⁠
⁠sub my_function3 {
⁠  my ( $param1, $param2, $param3 ) = @_; # the same as above in "my_function2"}
⁠
⁠my_function();                           # call the function "my_function"my_function;                             # also calls "my_function"&my_function;                            # also calls "my_function"my_function( "john", 28 );               # call "my_function" with 2 parametersmy_function "john", 28; # also calls "my_function" with 2 parameters: the brackets are not needed

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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