DocsHow-to GuidesRun Perl inside of your Flows

Run Perl inside of your Flows​Run ​Perl inside of your ​Flows

Run Perl code directly inside of your Flows and generate outputs.

There isn't an official Perl plugin but we can use the Shell Commands task to execute arbitrary commands inside of a Docker container. We can also specify a container image that contains the necessary libraries to run the specific programming language.

In this example, we're using the Docker Task Runner with the perl:latest image so that Perl can be executed.

yaml
id: perl_commands
namespace: company.team

tasks:
  - id: perl
    type: io.kestra.plugin.scripts.shell.Commands
    taskRunner:
      type: io.kestra.plugin.scripts.runner.docker.Docker
    containerImage: perl:latest
    namespaceFiles:
      enabled: true
    commands:
      - chmod +x main.pl
      - perl main.pl

The contents of the main.pl file contains a simple print statement:

perl
#!/usr/bin/perl

print "Hello World";

You'll need to add your Perl code using the Editor or sync it using Git so Kestra can see it. You'll also need to set the enabled flag for the namespaceFiles property to true so Kestra can access the file.

You can also have the Perl code written inline using the inputFiles property.

yaml
id: perl_commands
namespace: company.team

tasks:
  - id: perl
    type: io.kestra.plugin.scripts.shell.Commands
    taskRunner:
      type: io.kestra.plugin.scripts.runner.docker.Docker
    containerImage: perl:latest
    inputFiles:
      main.pl: |
        #!/usr/bin/perl
        print "Hello World";
    commands:
      - chmod +x main.pl
      - perl main.pl

You can read more about the Shell Commands type in the Plugin documentation.

Handling Outputs

If you want to get a variable or file from your Perl code, you can use an output.

Variable Output

You can get the JSON outputs from the Perl script using the ::{}:: pattern. Here is an example:

yaml
id: perl_outputs
namespace: company.team

tasks:
  - id: perl
    type: io.kestra.plugin.scripts.shell.Commands
    taskRunner:
      type: io.kestra.plugin.scripts.runner.docker.Docker
    containerImage: perl:latest
    inputFiles:
      main.pl: |
        #!/usr/bin/perl
        print '::{"outputs":{"test":"value","int":2,"bool":true,"float":3.65}}::';
    commands:
      - chmod +x main.pl
      - perl main.pl

All the output variables can be viewed in the Outputs tab of the execution.

perl_outputs

You can refer to the outputs in another task as shown in the example below:

yaml
id: perl_outputs
namespace: company.team

tasks:
  - id: perl
    type: io.kestra.plugin.scripts.shell.Commands
    taskRunner:
      type: io.kestra.plugin.scripts.runner.docker.Docker
    containerImage: perl:latest
    inputFiles:
      main.pl: |
        #!/usr/bin/perl
        print '::{"outputs":{"test":"value","int":2,"bool":true,"float":3.65}}::';
    commands:
      - chmod +x main.pl
      - perl main.pl

  - id: return
    type: io.kestra.plugin.core.debug.Return
    format: '{{ outputs.perl.vars.test }}'

File Output

Inside of your Perl code, write a file to the system. You'll need to add the outputFiles property to your flow and list the files you're trying to put out. In this case, we want to output output.txt. More information on the formats you can use for this property can be found here.

The example below writes a output.txt file containing the "Hello World" text. We can then refer the file using the syntax {{ outputs.{task_id}.outputFiles['<filename>'] }}, and read the contents of the file using the read() function.

yaml
id: perl_script
namespace: company.team

tasks:
  - id: perl
    type: io.kestra.plugin.scripts.shell.Commands
    taskRunner:
      type: io.kestra.plugin.scripts.runner.docker.Docker
    containerImage: perl:latest
    inputFiles:
      main.pl: |
        #!/usr/bin/perl
        use strict;
        use warnings;

        # Open the file for writing
        open(my $fh, '>', 'output.txt') or die "Cannot open file: $!";

        # Write to the file
        print $fh "Hello World";

        # Close the file
        close($fh);

        print "Successfully wrote to the file.\n";
    outputFiles:
      - output.txt
    commands:
      - chmod +x main.pl
      - perl main.pl

  - id: log
    type: io.kestra.plugin.core.log.Log
    message: "{{ read(outputs.perl.outputFiles['output.txt']) }}"

Handling Metrics

You can also get metrics from your Perl code. We use the same pattern for defining metrics as we had used for outputs ::{}::. In this example, we will demonstrate both the counter and timer metrics.

yaml
id: perl_metrics
namespace: company.team

tasks:
  - id: perl
    type: io.kestra.plugin.scripts.shell.Commands
    taskRunner:
      type: io.kestra.plugin.scripts.runner.docker.Docker
    containerImage: perl:latest
    inputFiles:
      main.pl: |
        #!/usr/bin/perl

        print "There are 20 products in the cart\n";
        print "::{\"outputs\":{\"productCount\":20}}::\n";
        print "::{\"metrics\":[{\"name\":\"productCount\",\"type\":\"counter\",\"value\":20}]}::\n";
        print "::{\"metrics\":[{\"name\":\"purchaseTime\",\"type\":\"timer\",\"value\":32.44}]}::\n";

    commands:
      - chmod +x main.pl
      - perl main.pl

Once this has executed, both the metrics can be viewed under Metrics.

metrics

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