Ansible: Passing arrays to BASH scripts

When using Ansible, it may become handy sooner or later to invoke a BASH script in one of you playbooks. Invoking a BASH script in Ansible can be done using a simple shell task:

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---
- hosts: 127.0.0.1
  connection: local
  tasks:
      - name: ensure stuff is done
        shell: ./do_stuff.sh

This task will execute the bash script do_stuff.sh. Sometimes, it is also necessary to configure the behaviour of the BASH script you are executing. The simplest way to do so is passing environment variables to the bash script as done in the following example.

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---
- hosts: 127.0.0.1
  connection: local
  tasks:
      - name: ensure custom stuff is done
        shell: ./do_stuff.sh
        environment:
            STUFF: some_stuff

In the BASH script we can now work with the environment variable as usual:

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#!/bin/bash

echo $STUFF > /tmp/stuff.txt

If we now want to pass multiple values in environment variable as array to the BASH script, we have two different options. Either we pass the array as string, or we parse the array output of Ansible in the bash script.

Option 1: Pass array as string

The first option is to pass the multiple values as string instead of a YAML array. In the following example, we separate them by spaces, which results in a single environment variable ARRAY being set when executing the BASH script.

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---
- hosts: 127.0.0.1
  connection: local
  tasks:
      - name: pass array as string
        shell: ./do_stuff_string.sh
        environment:
            ARRAY: one two three

To handle those values as array in our BASH script, we simply surround the value of the environment variable with parentheses. Afterwards the ARRAY variable is a BASH array containing the values one, two, and three.

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#!/bin/bash

ARRAY=($ARRAY)
:> /tmp/stuff_string.txt
for a in "${ARRAY[@]}"; do
    echo $a >> /tmp/stuff_string.txt
done

Option 2: Parse array

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---
- hosts: 127.0.0.1
  connection: local
  tasks:
      - name: pass array as array
        shell: ./do_stuff_array.sh
        environment:
            ARRAY:
            - one
            - two
            - three

Unfortunately, this environment variable is still set as string, now containing a python string representation of the array:

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[u'one', u'two', u'three']

To parse the array in the BASH script, the simplest way is to use python again, which is able to handle this value out of the box.

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#!/bin/bash

ARRAY=($(python <<< "print(' '.join($ARRAY))"))
:> /tmp/stuff_array.txt
for a in "${ARRAY[@]}"; do
    echo $a >> /tmp/stuff_array.txt
done

With the python one-liner in line 3, ARRAY again is a BASH array with the values one, two, and three and can be processed further.

Please note that, to be able to get array elements with spaces passed by ansible, we need to change the array seperator as the following version of the script shows. Otherwise, bash would recognize every single word as separate element of the array:

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#!/bin/bash
IFS=

We have seen 2 different options to pass an array from Ansible to a BASH script. Option 1, passing it as a simple string variable has some implications, for example an array containing values with spaces might result in a less readable YAML line. Option 2, defining the array as YAML array and parsing it in your BASH script with python makes the definition better readable and more solid, but adds a dependency to python for your BASH script.

If simple one-word arguments need to be set for your script, option 1 might still be a good option as it is easier to handle in the BASH script and doesn’t include a dependency to python.
Nevertheless, for more complex playbooks or values in the array, I recommend option 2 as the cleaner solution.

n’
ARRAY=( $(python <<< “print(‘n’.join($ARRAY))”) )
echo “${ARRAY[@]}”
for a in “${ARRAY[@]}”; do
echo “$a”
done
We have seen 2 different options to pass an array from Ansible to a BASH script. Option 1, passing it as a simple string variable has some implications, for example an array containing values with spaces might result in a less readable YAML line. Option 2, defining the array as YAML array and parsing it in your BASH script with python makes the definition better readable and more solid, but adds a dependency to python for your BASH script.

If simple one-word arguments need to be set for your script, option 1 might still be a good option as it is easier to handle in the BASH script and doesn’t include a dependency to python.
Nevertheless, for more complex playbooks or values in the array, I recommend option 2 as the cleaner solution.

Categorised in: Uncategorized

This post was written by Manuel Dewald