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.

`sed -i 's/^# autologin=.*/autologin=ubuntu/' /some/file`? – muru Oct 15 '16 at 08:48 — muru, Oct 15 '16 at 08:48

Zanna · Accepted Answer · 2016-10-15T09:22:06.723

54

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

edited Oct 15 '16 at 09:22

answered Oct 15 '16 at 08:49

Zanna

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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 – lewis4u Oct 15 '16 at 08:51
yes, exactly like that @lewis4u – Zanna Oct 15 '16 at 08:52
No `/g` at the end? – Tjorriemorrie Aug 30 '21 at 14:40
@Tjorriemorrie `g` means apply the command to every occurrence on the line specified, which is not relevant to this case – Zanna Aug 30 '21 at 15:26
`sed 's/# 1/1' /etc/gai.conf` gives sed: -e expression #1, char 7: unterminated `s' command – Gulzar Jan 20 '22 at 16:36
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@Gulzar yes, you need a final `/` before your closing quote, i.e. `sed 's/# 1/1/' /etc/gai.conf` – Zanna Jan 20 '22 at 17:26

score 5 · Answer 2 · answered Mar 19 '20 at 03:14

5

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

answered Mar 19 '20 at 03:14

dragon788

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You could mention that % is used to replace the / delimiter. Got me questioning my sanity for a while... – Sherlock70 Mar 30 '23 at 14:19

Sed replace specific line in file

2 Answers2