Ansible File Editing with lineinfile and blockinfile

Templates, Files and Vault / Guide 19 of 45 / Intermediate

• OSUbuntu 26.04 LTS
• ansible-core2.20.1
• Python3.14.4
• TimeAbout 16 min

lineinfile acts on the last line matching regexp. If several lines match, the others are left alone - which is why replace exists, and why a config with a repeated directive needs care.

This guide includes

Use this when you cannot template a file because you do not own all of it. This matters because lineinfile without a regexp duplicates rather than replaces - which is the trap this guide exists to show you.

• editing one line with lineinfile and a regexp
• hitting the duplicate trap by leaving the regexp out
• using replace when every match should change
• using blockinfile when it is more than a single line

Before you start

• A control node configured as shown in the first step.
• The session creates /etc/demo.conf containing a deliberately duplicated Timeout line.

1. 1

   The configuration this guide assumes

2. 2

   A file to edit

3. 3

   lineinfile with a regexp

4. 4

   The duplicate trap

5. 5

   replace changes every match

6. 6

   blockinfile for more than one line

Official sources

• ansible.builtin.lineinfile
• ansible.builtin.blockinfile
• ansible.builtin.replace