Replace only whole line containing a string using Sed

Question

In zabbix-agent.conf I have lines:

#   Example: Server=127.0.0.1,192.168.1.0/24,::1,2001:db8::/32,zabbix.example.com
Server=127.0.0.1

I want to replace line

Server=127.0.0.1

with my

Server=zabbix.mydomain.com

But if I do

sed -i -e 's/Server=127.0.0.1/Server=zabbix.mydomain.com/g' /etc/zabbix/zabbix_agentd.conf

it found also line with commented example and replace string in it. I get:

#<----->Example: Server=zabbix.mydomain.com,192.168.1.0/24,::1,2001:db8::/32,zabbix.example.com
Server=zabbix.mydomain.com

How to replace only one line?

Answer 1

You need to

• Match the text at the start of string
• Escape the dots
• Remove g flag since the match will only be found at the string start.

Also, you do not need the -e option, you can use

sed -i 's/^Server=127\.0\.0\.1/Server=zabbix.mydomain.com/' /etc/zabbix/zabbix_agentd.conf

See the online demo:

#!/bin/bash
s='#   Example: Server=127.0.0.1,192.168.1.0/24,::1,2001:db8::/32,zabbix.example.com
Server=127.0.0.1'
sed 's/^Server=127\.0\.0\.1/Server=zabbix.mydomain.com/g' <<< "$s"

Output:

   Example: Server=127.0.0.1,192.168.1.0/24,::1,2001:db8::/32,zabbix.example.com
Server=zabbix.mydomain.com

Answer 2

This might work for you (GNU sed):

sed -i '/^Server=127\.0\.0\.1/cServer=zabbix.mydomain.com' file

Change line beginning Server=127.0.0.1 to Server=zabbix.mydomain.com.

Answer 3

The other answers are almost fine but they would also replace a line like:

Server=127.0.0.10

A complete solution with any sed could be:

sed -i 's/^Server=127\.0\.0\.1$/Server=zabbix.mydomain.com/' /etc/zabbix/zabbix_agentd.conf

^ and $ anchor the string to the beginning and end of line, respectively. Dots need backslash escape, else they stand for any character.