Replace a string with another substring using sed in shell script

Question

For every line except the first line in my file,I want to check if a string already exists . If it does, then do nothing. Otherwise, append the string to the line

For ex - there are foll 3 lines in my file

line1 : do_not_modify

line2-string-exists

line3

I want to append -string-exists to only those lines in the file which does not have that string appended to them(Ignore the first line)

the output should be -

line1 : do_not_modify

line2-string-exists

line3-string-exists

Please tell me How will I do it using sed? Or is it possible to do with awk?

It is possible to solve the problem with sed or awk. What have you tried so far? — Michael Vehrs
– Michael Vehrs, Commented Jun 1, 2016 at 6:30

riteshtch · Accepted Answer · 2016-06-01 13:43:02Z

4

$ cat data
line1 : do_not_modify
line2-string-exists
line3

$ sed '1!{/-string-exists/! s/$/-string-exists/}' data
line1 : do_not_modify
line2-string-exists
line3-string-exists

or using awk:

$ awk '{if(NR!=1 && ! /-string-exists/) {printf "%s%s", $0, "-string-exists\n"} else {print}}' data
line1 : do_not_modify
line2-string-exists
line3-string-exists

edited Jun 1, 2016 at 13:43

answered Jun 1, 2016 at 6:28

riteshtch

8,7994 gold badges28 silver badges39 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Manisha Over a year ago

Thanks! curly braces were missing from my command. It is working now

anubhava · Accepted Answer · 2016-06-01 06:30:42Z

1

You can use this sed command:

sed -E '/(do_not_modify|-string-exists)$/!s/$/-string-exists/' file

line1 : do_not_modify
line2-string-exists
line3-string-exists

Or using awk:

awk '!/(do_not_modify|-string-exists)$/{$0 = $0 "-string-exists"} 1' file

answered Jun 1, 2016 at 6:30

anubhava

790k67 gold badges603 silver badges671 bronze badges

2 Comments

Ed Morton Over a year ago

I don't think "do_not_modify" is actually present in the input file.

anubhava Over a year ago

Yes may be OP would have wanted awk 'NR>1 && !/-string-exists$/{$0 = $0 "-string-exists"} 1' file

Ed Morton · Accepted Answer · 2016-06-01 12:20:23Z

0

Assuming the string doesn't contain any RE metacharacters:

$ awk 'BEGIN{s="-string-exists"} (NR>1) && ($0!~s"$"){$0=$0 s} 1' file
line1 : do_not_modify
line2-string-exists
line3-string-exists

answered Jun 1, 2016 at 12:20

Ed Morton

209k18 gold badges90 silver badges212 bronze badges

Collectives™ on Stack Overflow

Replace a string with another substring using sed in shell script

3 Answers 3

1 Comment

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related