Sed replace specific line in file

Question

I'm building a bash script for my virtual machine and I would like to know how to replace a specific line in this document:

[base]

## uncomment and set autologin username to enable autologin
# autologin=dgod

## uncomment and set timeout to enable timeout autologin,

## the value should >=5

# timeout=10

## default session or desktop used when no systemwide config

# session=/usr/bin/startlxde

this line:

# autologin=dgod

I want to change to this

autologin=ubuntu

I have tried with "tee" and "sed" but couldn't make it work. This should be very easy for someone who works with bash scripts more often than me.

Solution 1

It is straightforward. Use the s command in sed to search and replace.

sed 's/# autologin=dgod/autologin=ubuntu/' /path/to/file

If you see what you want, add -i to change the file in place

sed -i 's/# autologin=dgod/autologin=ubuntu/' /path/to/file

Solution 2

I've found the most effective way to do this is actually to use the change syntax to set the exact value you want unless you are explicitly trying to enable a two way toggle. You can use this to change as well as uncomment a line no matter how it is commented, with # or // or <!--.

sed 's%searchTerm=% c searchTerm=desiredValue%' targetFile.txt

Comments

[Admin]

sed -i 's/^# autologin=.*/autologin=ubuntu/' /some/file?

[lewis4u]

the filename is /etc/lxdm/default.conf - so the full command should be like this? = sed -i 's/# autologin=dgod/autologin=ubuntu/' /etc/lxdm/default.conf

[Zanna]

yes, exactly like that @lewis4u

[Tjorriemorrie]

No /g at the end?

[Zanna]

@Tjorriemorrie g means apply the command to every occurrence on the line specified, which is not relevant to this case

[Gulzar]

sed 's/# 1/1' /etc/gai.conf gives sed: -e expression #1, char 7: unterminated `s' command

[Zanna]

@Gulzar yes, you need a final / before your closing quote, i.e. sed 's/# 1/1/' /etc/gai.conf