Jinja2 filters

• Filters For Formatting Data
• Forcing Variables To Be Defined
• Defaulting Undefined Variables
• Omitting Parameters
• List Filters
• Set Theory Filters
• Random Number Filter
• Shuffle Filter
• Math
• IP address filter
• Hashing filters
• Combining hashes/dictionaries
• Extracting values from containers
• Comment Filter
• Other Useful Filters
• Debugging Filters

Filters in Jinja2 are a way of transforming template expressions from one kind of data into another. Jinja2 ships with many of these. See builtin filters in the official Jinja2 template documentation.

Take into account that filters always execute on the Ansible controller, not on the task target, as they manipulate local data.

In addition to those, Ansible supplies many more.

Filters For Formatting Data

The following filters will take a data structure in a template and render it in a slightly different format. These are occasionally useful for debugging:

{{ some_variable | to_json }}
{{ some_variable | to_yaml }}

For human readable output, you can use:

{{ some_variable | to_nice_json }}
{{ some_variable | to_nice_yaml }}

It’s also possible to change the indentation of both (new in version 2.2):

{{ some_variable | to_nice_json(indent=2) }}
{{ some_variable | to_nice_yaml(indent=8) }}

Alternatively, you may be reading in some already formatted data:

{{ some_variable | from_json }}
{{ some_variable | from_yaml }}

for example:

tasks:
  - shell: cat /some/path/to/file.json
    register: result

  - set_fact: myvar="{{ result.stdout | from_json }}"

Forcing Variables To Be Defined

The default behavior from ansible and ansible.cfg is to fail if variables are undefined, but you can turn this off.

This allows an explicit check with this feature off:

{{ variable | mandatory }}

The variable value will be used as is, but the template evaluation will raise an error if it is undefined.

Defaulting Undefined Variables

Jinja2 provides a useful ‘default’ filter, that is often a better approach to failing if a variable is not defined:

{{ some_variable | default(5) }}

In the above example, if the variable ‘some_variable’ is not defined, the value used will be 5, rather than an error being raised.

Omitting Parameters

As of Ansible 1.8, it is possible to use the default filter to omit module parameters using the special omit variable:

- name: touch files with an optional mode
  file: dest={{item.path}} state=touch mode={{item.mode|default(omit)}}
  with_items:
    - path: /tmp/foo
    - path: /tmp/bar
    - path: /tmp/baz
      mode: "0444"

For the first two files in the list, the default mode will be determined by the umask of the system as the mode= parameter will not be sent to the file module while the final file will receive the mode=0444 option.

List Filters

These filters all operate on list variables.

To get the minimum value from list of numbers:

{{ list1 | min }}

To get the maximum value from a list of numbers:

{{ [3, 4, 2] | max }}

Set Theory Filters

All these functions return a unique set from sets or lists.

To get a unique set from a list:

{{ list1 | unique }}

To get a union of two lists:

{{ list1 | union(list2) }}

To get the intersection of 2 lists (unique list of all items in both):

{{ list1 | intersect(list2) }}

To get the difference of 2 lists (items in 1 that don’t exist in 2):

{{ list1 | difference(list2) }}

To get the symmetric difference of 2 lists (items exclusive to each list):

{{ list1 | symmetric_difference(list2) }}

Random Number Filter

This filter can be used similar to the default jinja2 random filter (returning a random item from a sequence of items), but can also generate a random number based on a range.

To get a random item from a list:

{{ ['a','b','c']|random }} => 'c'

To get a random number from 0 to supplied end:

{{ 59 |random}} * * * * root /script/from/cron

Get a random number from 0 to 100 but in steps of 10:

{{ 100 |random(step=10) }}  => 70

Get a random number from 1 to 100 but in steps of 10:

{{ 100 |random(1, 10) }}    => 31
{{ 100 |random(start=1, step=10) }}    => 51

Shuffle Filter

This filter will randomize an existing list, giving a different order every invocation.

To get a random list from an existing list:

{{ ['a','b','c']|shuffle }} => ['c','a','b']
{{ ['a','b','c']|shuffle }} => ['b','c','a']

note that when used with a non ‘listable’ item it is a noop, otherwise it always returns a list

Math

Get the logarithm (default is e):

{{ myvar | log }}

Get the base 10 logarithm:

{{ myvar | log(10) }}

Give me the power of 2! (or 5):

{{ myvar | pow(2) }}
{{ myvar | pow(5) }}

Square root, or the 5th:

{{ myvar | root }}
{{ myvar | root(5) }}

Note that jinja2 already provides some like abs() and round().

IP address filter

To test if a string is a valid IP address:

{{ myvar | ipaddr }}

You can also require a specific IP protocol version:

{{ myvar | ipv4 }}
{{ myvar | ipv6 }}

IP address filter can also be used to extract specific information from an IP address. For example, to get the IP address itself from a CIDR, you can use:

{{ '192.0.2.1/24' | ipaddr('address') }}

More information about ipaddr filter and complete usage guide can be found in Jinja2 ‘ipaddr()’ filter.

Hashing filters

To get the sha1 hash of a string:

{{ 'test1'|hash('sha1') }}

To get the md5 hash of a string:

{{ 'test1'|hash('md5') }}

Get a string checksum:

{{ 'test2'|checksum }}

Other hashes (platform dependent):

{{ 'test2'|hash('blowfish') }}

To get a sha512 password hash (random salt):

{{ 'passwordsaresecret'|password_hash('sha512') }}

To get a sha256 password hash with a specific salt:

{{ 'secretpassword'|password_hash('sha256', 'mysecretsalt') }}

Hash types available depend on the master system running ansible, ‘hash’ depends on hashlib password_hash depends on crypt.

Combining hashes/dictionaries

The combine filter allows hashes to be merged. For example, the following would override keys in one hash:

{{ {'a':1, 'b':2}|combine({'b':3}) }}

The resulting hash would be:

{'a':1, 'b':3}

The filter also accepts an optional recursive=True parameter to not only override keys in the first hash, but also recurse into nested hashes and merge their keys too:

{{ {'a':{'foo':1, 'bar':2}, 'b':2}|combine({'a':{'bar':3, 'baz':4}}, recursive=True) }}

This would result in:

{'a':{'foo':1, 'bar':3, 'baz':4}, 'b':2}

The filter can also take multiple arguments to merge:

{{ a|combine(b, c, d) }}

In this case, keys in d would override those in c, which would override those in b, and so on.

This behaviour does not depend on the value of the hash_behaviour setting in ansible.cfg.

Extracting values from containers

The extract filter is used to map from a list of indices to a list of values from a container (hash or array):

{{ [0,2]|map('extract', ['x','y','z'])|list }}
{{ ['x','y']|map('extract', {'x': 42, 'y': 31})|list }}

The results of the above expressions would be:

['x', 'z']
[42, 31]

The filter can take another argument:

{{ groups['x']|map('extract', hostvars, 'ec2_ip_address')|list }}

This takes the list of hosts in group ‘x’, looks them up in hostvars, and then looks up the ec2_ip_address of the result. The final result is a list of IP addresses for the hosts in group ‘x’.

The third argument to the filter can also be a list, for a recursive lookup inside the container:

{{ ['a']|map('extract', b, ['x','y'])|list }}

This would return a list containing the value of b[‘a’][‘x’][‘y’].

Comment Filter

The comment filter allows to decorate the text with a chosen comment style. For example the following:

{{ "Plain style (default)" | comment }}

will produce this output:

#
# Plain style (default)
#

Similar way can be applied style for C (//...), C block (/*...*/), Erlang (%...) and XML (<!--...-->):

{{ "C style" | comment('c') }}
{{ "C block style" | comment('cblock') }}
{{ "Erlang style" | comment('erlang') }}
{{ "XML style" | comment('xml') }}

It is also possible to fully customize the comment style:

{{ "Custom style" | comment('plain', prefix='#######\n#', postfix='#\n#######\n   ###\n    #') }}

That will create the following output:

#######
#
# Custom style
#
#######
   ###
    #

The filter can also be applied to any Ansible variable. For example to make the output of the ansible_managed variable more readable, we can change the definition in the ansible.cfg file to this:

[defaults]

ansible_managed = This file is managed by Ansible.%n
  template: {file}
  date: %Y-%m-%d %H:%M:%S
  user: {uid}
  host: {host}

and then use the variable with the comment filter:

{{ ansible_managed | comment }}

which will produce this output:

#
# This file is managed by Ansible.
#
# template: /home/ansible/env/dev/ansible_managed/roles/role1/templates/test.j2
# date: 2015-09-10 11:02:58
# user: ansible
# host: myhost
#

Other Useful Filters

To add quotes for shell usage:

- shell: echo {{ string_value | quote }}

To use one value on true and another on false (new in version 1.9):

{{ (name == "John") | ternary('Mr','Ms') }}

To concatenate a list into a string:

{{ list | join(" ") }}

To get the last name of a file path, like ‘foo.txt’ out of ‘/etc/asdf/foo.txt’:

{{ path | basename }}

To get the last name of a windows style file path (new in version 2.0):

{{ path | win_basename }}

To separate the windows drive letter from the rest of a file path (new in version 2.0):

{{ path | win_splitdrive }}

To get only the windows drive letter:

{{ path | win_splitdrive | first }}

To get the rest of the path without the drive letter:

{{ path | win_splitdrive | last }}

To get the directory from a path:

{{ path | dirname }}

To get the directory from a windows path (new version 2.0):

{{ path | win_dirname }}

To expand a path containing a tilde (~) character (new in version 1.5):

{{ path | expanduser }}

To get the real path of a link (new in version 1.8):

{{ path | realpath }}

To get the relative path of a link, from a start point (new in version 1.7):

{{ path | relpath('/etc') }}

To get the root and extension of a path or filename (new in version 2.0):

# with path == 'nginx.conf' the return would be ('nginx', '.conf')
{{ path | splitext }}

To work with Base64 encoded strings:

{{ encoded | b64decode }}
{{ decoded | b64encode }}

To create a UUID from a string (new in version 1.9):

{{ hostname | to_uuid }}

To cast values as certain types, such as when you input a string as “True” from a vars_prompt and the system doesn’t know it is a boolean value:

- debug: msg=test
  when: some_string_value | bool

To replace text in a string with regex, use the “regex_replace” filter:

# convert "ansible" to "able"
{{ 'ansible' | regex_replace('^a.*i(.*)$', 'a\\1') }}

# convert "foobar" to "bar"
{{ 'foobar' | regex_replace('^f.*o(.*)$', '\\1') }}

# convert "localhost:80" to "localhost, 80" using named groups
{{ 'localhost:80' | regex_replace('^(?P<host>.+):(?P<port>\\d+)$', '\\g<host>, \\g<port>') }}

To escape special characters within a regex, use the “regex_escape” filter:

# convert '^f.*o(.*)$' to '\^f\.\*o\(\.\*\)\$'
{{ '^f.*o(.*)$' | regex_escape() }}

To make use of one attribute from each item in a list of complex variables, use the “map” filter (see the Jinja2 map() docs for more):

# get a comma-separated list of the mount points (e.g. "/,/mnt/stuff") on a host
{{ ansible_mounts|map(attribute='mount')|join(',') }}

To get date object from string use the to_datetime filter, (new in version in 2.2):

# get amount of seconds between two dates, default date format is %Y-%d-%m %H:%M:%S but you can pass your own one
{{ (("2016-08-04 20:00:12"|to_datetime) - ("2015-10-06"|to_datetime('%Y-%d-%m'))).seconds  }}

Debugging Filters

Use the type filter to display the underlying Python type of a variable. This can be useful in debugging in situations where you may need to know the exact type of a variable:

{{ myvar | type }}

A few useful filters are typically added with each new Ansible release. The development documentation shows how to extend Ansible filters by writing your own as plugins, though in general, we encourage new ones to be added to core so everyone can make use of them.