Change variable value inside text file with Sed

Question

I have a text file containting this

Var1=ofzer
Var2=smelf
..
..
VarN=mskfm

I want to change the value of one of my variables using Sed. How is that possible?

Have a look at http://www.grymoire.com/Unix/Sed.html#uh-1 - this is a simple example of substitution using sed. — Josh Jolly, Mar 06 '14 at 15:58
You'll need to use a regular expression as an *address* to find the line to change. Then use the *"s" command* to change the value. Use the `-i` option to edit the file in-place. Here's the [GNU sed manual](https://www.gnu.org/software/sed/manual/sed.html) — glenn jackman, Mar 06 '14 at 15:59
possible duplicate of [sed scripting - environment variable substitution](http://stackoverflow.com/questions/584894/sed-scripting-environment-variable-substitution) — tripleee, Nov 24 '14 at 06:27

score 18 · Answer 1 · answered Mar 06 '14 at 20:53

18

Say you wanted to change the value of Var2 from 'smelf' to 'smurf', you could use:

bash$ sed -i 's/Var2=.*/Var2=smurf/' file.txt

answered Mar 06 '14 at 20:53

problemPotato

Suppose I want to set it to `${NEW_VALUE}`? I can't use `${var}` inside of single quotes and, if I switch to double-quotes, the `.*` part doesn't work (does it?!) So now what? – Olie Sep 23 '14 at 00:02
You can use double quotes. – Alberto Salvia Novella May 13 '21 at 08:14

score 2 · Answer 2 · answered Nov 23 '14 at 22:41

2

In case you want more complex substitution:

sed_param=s/Var1=.*/Var1=${NEW_VALUE}/  
sed -i "$sed_param" file.txt

answered Nov 23 '14 at 22:41

andrey

2 Answers2