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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

closed as too broad by Jeff Schaller, Isaac, Kiwy, Anthony Geoghegan, Archemar May 9 '18 at 15:56

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • 3
    Use sed which is the right tool for your requirements – αғsнιη May 8 '18 at 19:57
  • Use ed which might be a better tool for your requirement – Valentin Bajrami May 8 '18 at 20:02
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    Are these ert and ghf values one-time (static) changes, or does the script need to prompt for add/remove and the value? – Jeff Schaller May 8 '18 at 20:03
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    How do you know when you want to remove ert? I don't see an example of how you'd expect to do that. – Andy Dalton May 8 '18 at 20:04
  • Cross-post of – Isaac May 9 '18 at 6:54
1

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.
  • 1
    good suggestion. However you are making sed do too much work: there's no need to match everything only to put it into the replacement. Just match the end-of-line and add the new value there. Also, you need double quotes for the shell to expand the variable: sed -i "/^values = / s/$/$NEW_VALUE/" file – glenn jackman May 8 '18 at 22:40
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    Same with the next one: sed -ir "/^values = / s/ $REMOVE_VALUE,//" file – glenn jackman May 8 '18 at 22:43
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    In general, you don't need .* at the beginning or end of the pattern if you're going to just put them into the replacement unchanged. – glenn jackman May 8 '18 at 22:44
  • @glennjackman Wow, very good observation! Thank you very much, I'll update the answer – Iskustvo May 8 '18 at 22:45
0

Using ed you can do the following:

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

and

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

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