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@iAugur
Last active May 14, 2024 12:37
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Ansible: Add a String to an existing line in a file
# Adapted from solution provided by http://stackoverflow.com/users/57719/chin-huang http://stackoverflow.com/a/31465939/348868
# Scenario: You want to add a group to the list of the AllowGroups in ssh_config
# before:
# AllowGroups Group1
# After:
# AllowGroups Group1 Group2
- name: Add Group to AllowGroups
replace:
backup: yes
dest: /etc/ssh/sshd_config
regexp: '^(AllowGroups(?!.*\b{{ sftp_group_name }}\b).*)$'
replace: '\1 {{ sftp_group_name }}'
# This could also be achieved using the line in file module:
- name: Add Group to AllowGroups
lineinfile:
dest=/etc/ssh/sshd_config
backup=True
backrefs=True
state=present
regexp='^(AllowGroups(?!.*\b{{ sftp_group_name }}\b).*)$'
line='\1 {{ sftp_group_name }}'
@iAugur
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iAugur commented Aug 30, 2022

The /1 and /2 are the two matched groups in the regular expression. Tthere are three groups are 'marked' by the bracked expressions.
The \b in the second group marks a word boundary and that expression is saying where this word is not found. So in essence it says grab the bit in the first brackets as /1 check for the abscence of the whole word in the second group and grab the last matched group as /2. There are three groups but if the second group matches them your expression fails - so if it succeeds there will only be two.
e.g. if you have /1 /2 /3 it fails as your value was there
if you have /1 /2 it matches

@ykfq
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ykfq commented Feb 22, 2024

great!
Note this is not idempotent.

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