Replace value of a variable in a file through script using sed

Shell Programming and Scripting
1

Hi,

I am trying to replace the value of a variable in a file through another script.

Example:
Filename : abc.txt contents:
a=10
b=20
c=30

Need to change the value of, say, b - Tried using the following:

sed "s/${b}/15/g" abc.txt

Have tried various forms of sed (with single quotes, without quotes, with -e option, etc) but getting the same error with all:

sed: -e expression #1, char 0: no previous regular expression

:wall:

Thanks for any help in advance :slight_smile:

2

You are getting that error because the shell variable, ${b} , is unset or null. After its expansion, the sed command becomes s//15/g . In sed, an empty regular expression is equivalent to the most recently used regular expression. Since there is none, you get that error.

Regards,
Alister

3

Thanks Alister...

Is there any way this can be overcome - so that I can have variable in the file referenced directly

4

how about:

sed "s/^b=.*/b=${b}/" abc.txt
1 Like
5

It worked - Thanks Chubler_XL :b: