sed command to replace first occurrence in file is not working

Question

I am trying to replace first string occurrence in file. eg Trying to replace first foo with linux

sample.txt

Hi foo bar
This is again foo bar.

Command: sed '0,/foo/s//linux/' sample.txt

Actual output from above command (basically no change)

Hi foo bar
This is again foo bar.

My expected output is as below

Hi linux bar
This is again foo bar.

Could anyone please help here?

Answer 1

/tmp/test.txt

Hi foo bar!
This is again foo bar

Use the following sed commando to replace only the first orrouance of the search-string;

sed -e '1 s/foo/linux/; t' -e '1,// s//linux/' /tmp/test.txt

Result :

Hi linux bar!
This is again foo bar

---

• Terminal output + OSX version

• Terminal output; first foo on 3th line

Answer 2

With any awk following may help:

awk '/foo/ && ++count==1{sub(/foo/,"linux")} 1' Input_file

With GNU sed if one has enough memory in box following may help:

sed -z 's/foo/linux/' Input_file

Answer 3

With awk

awk '!f && sub(/foo/, "linux"){f=1} 1' ip.txt

• !f will be true as uninitialized variables are falsey by default
• sub(/foo/, "linux") will replace first occurrence of foo and returns 1 - thus making f=1 and subsequent !f to be always false
• 1 to print $0