Grab nth occurrence in between two patterns using awk or sed - shell

Question

I have an issue where I want to parse through the output from a file and I want to grab the nth occurrence of text in between two patterns preferably using awk or sed
category
1
s
t
done
category
2
n
d
done
category
3
r
d
done
category
4
t
h
done
Let's just say for this example I want to grab the third occurrence of text in between category and done, essentially the output would be
category
3
r
d
done

Answer 1

This might work for you (GNU sed):
'sed -n '/category/{:a;N;/done/!ba;x;s/^/x/;/^x\{3\}$/{x;p;q};x}' file
Turn off automatic printing by using the -n option. Gather up lines between category and done. Store a counter in the hold space and when it reaches 3 print the collection in the pattern space and quit.
Or if you prefer awk:
awk '/^category/,/^done/{if(++m==1)n++;if(n==3)print;if(/^done/)m=0}' file

Answer 2

Try doing this :
awk -v n=3 '/^category/{l++} (l==n){print}' file.txt
Or more cryptic :
awk -v n=3 '/^category/{l++} l==n' file.txt
If your file is big :
awk -v n=3 '/^category/{l++} l>n{exit} l==n' file.txt

Answer 3

If your file doesn't contain any null characters, here's on way using GNU sed. This will find the third occurrence of a pattern range. However, you can easily modify this to get any occurrence you'd like.
sed -n '/^category/ { x; s/^/\x0/; /^\x0\{3\}$/ { x; :a; p; /done/q; n; ba }; x }' file.txt
Results:
category
3
r
d
done
Explanation:
Turn off default printing with the -n switch. Match the word 'category' at the start of a line. Swap the pattern space with the hold space and append a null character to the start of the pattern. In the example, if the pattern then contains two leading null characters, pull the pattern out of holdspace. Now create a loop and print the contents of the pattern space until the last pattern is matched. When this last pattern is found, sed will quit. If it's not found sed will continue to read the next line of input in and continue in its loop.

Answer 4

awk -v tgt=3 '
/^category$/ { fnd=1; rec="" }
fnd {
rec = rec $0 ORS
if (/^done$/) {
if (++cnt == tgt) {
printf "%s",rec
exit
}
fnd = 0
}
}
' file

Answer 5

With GNU awk you can set the the record separator to a regular expression:
<file awk 'NR==n+1 { print rt, $0 } { rt = RT }' RS='\\<category' ORS='' n=3
Output:
category
3
r
d
done
RT is the matched record separator. Note that the record relative to n will be off by one as the first record refers to what precedes the first RS.
Edit
As per Ed's comment, this will not work when the records have other data in between them, e.g.:
category
1
s
t
done
category
2
n
d
done
foo
category
3
r
d
done
bar
category
4
t
h
done
One way to get around this is to clean up the input with a second (or first) awk:
<file awk '/^category$/,/^done$/' |
awk 'NR==n+1 { print rt, $0 } { rt = RT }' RS='\\<category' ORS='' n=3
Output:
category
3
r
d
done
Edit 2
As Ed has noted in the comments, the above methods do not search for the ending pattern. One way to do this, which hasn't been covered by the other answers, is with getline (note that there are some caveats with awk getline):
<file awk '
/^category$/ {
v = $0
while(!/^done$/) {
if(!getline)
exit
v = v ORS $0
}
if(++nr == n)
print v
}' n=3
On one line:
<file awk '/^category$/ { v = $0; while(!/^done$/) { if(!getline) exit; v = v ORS $0 } if(++nr == n) print v }' n=3