regex - how can I get sed to quit after the first matching address range?

Question

I have a file:

header
trigger
text1
text2
trigger
text5
trigger
...
trigger
...

I want sed to only match between the first two occurrences of 'trigger'. So I tried:

sed -n '/trigger/,/trigger/p'

But as the man page for sed says, that matches all occurrences within two lines with 'trigger'. I want sed to quit after the first match, so the output would be:

trigger
text1
text2
trigger

How do I accomplish this?

Answer 1

You can do this with a loop in GNU sed:

sed -n '/trigger/{p; :loop n; p; /trigger/q; b loop}'

Explanation:

1. When you see the first /trigger/, start a block of commands
2. p -- print the line
3. :loop -- set a label named loop
4. n -- get the next line
5. p -- print the line
6. /trigger/q -- if the line matches /trigger/ then exit sed
7. b -- jump to loop