I have a file test.txt which has a line like below

values = abc, def, dfg, ert, sdf, sfd, sdf 

I use the shell script to add a new value with comma separation in the values in the test,txt.

For example, I need to add the 'ghf' in the test.txt:

values = abc, def, dfg, ert, sdf, sfd, sdf, ghf 

Also I need to remove the value.

For example, if I need to remove the 'ert' in the test.txt:

values = abc, def, dfg, sdf, sfd, sdf, ghf 

How can I achieve this in shell script?

(i.e)

If I give the

echo "abc" >> test.txt

It is able to append the "abc" to the end of the file
but I need to append to the 'values=' field in test.txt

Thanks,

Hari

Fast solution without a guard from corner cases.

(Thanks glenn jackman for sed optimizations.)

Adding

sed -i "/^values = / s/$/, $NEW_VALUE/" test.txt

Explanation

sed -i - Make changes in the given file, do not print to the stdout.

/^values = / - When sed is positioned on the line that starts with values =.

s/$/, $NEW_VALUE/ - Append , $NEW_VALUE at the end of the line.

test.txt - File on which sed will perform actions.

Removing

sed -i "/^values = / s/ $REMOVE_VALUE,?//" test.txt

Explanation

s/ $REMOVE_VALUE,?// - Remove the first occurence of $REMOVE_VALUE along with optional following ,.

Problems with this solution

1. Adding the first value will add , right after values =
   


2. Removing the last value will leave the line ending with ,.


3. If added/removed variables containt sed's separator for s command (in my example it is /), command won't work.

Using ed you can do the following:

ed -s test.txt <<<$'/values/s/$/,ghfnw' # add ghf to the end of line

and

ed -s values <<<$'/values/s/ert,//nw' # remove ert