Introducing Command::Template.

In recent post IPC::Cmd considered harmful I expressed my (low) opinion for IPC::Cmd. The reason why I had to endure some time with that module was that I was working on Command::Template.

This new module allows defining objects that ease the creation of command lines based on a… template. As a useful twist, it’s also possible to get an object that actually runs those generated commands, although with limitations.

The typical template resembles those in the examples, where angular parentheses indicate mandatory parameters and square brackets optional ones. Well… I might probably do better, so let’s just consider the API a little alpha so far.

As an example, let’s consider the following:

use Command::Template 'command_template':
my $ct = command_template(qw{ ls [options=-l] <dir> });

This template above requires a parameter dir when invoked, and also accepts an optional parameter options whose default value is -l. In other terms, it represents invocations of the following kinds:

# the root dir with the default options
ls -l /

# just the plain dir
ls /

# another dir with different options
ls -la /etc

# another dir with different, separated options
ls -l -a /var

but not, for example, a plain ls -l (in the current directory) because the <dir> parameter marks a required element.

To obtain the example expansions above we would need to call $ct->generate with different bindings, i.e. name/value pairs that tell it how to map each parameter’s name to the corresponding value. Bindings are passed as a list of alternating key/value pairs, so any hash would do:

# the root dir with the default options
# ('ls', '-l', '/')
@cmd = $ct->generate(dir => '/');

# just the plain dir
# ('ls', '/')
@cmd = $ct->generate(dir => '/', options => []);    # OR
@cmd = $ct->generate(dir => '/', options => undef); # ALTERNATIVE FORM

# another dir with different options
# ('ls', '-la', '/etc')
@cmd = $ct->generate(dir => '/etc'), options => '-la');

# another dir with different, separated options
# ('ls', '-l', '-a', '/var')
@cmd = $ct->generate(dir => '/var', options => ['-l', '-a']);

The command that is generated can then be used in facilities that accept an array for executing, e.g. system, exec, IPC::Run (and IPC::Cmd, of course, although that would not actually use it as a real array):

my $exit_value = system {$cmd[0]} @cmd;

Well, enough for today I guess… stay safe and hold on, spring is coming!

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