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Test file is given below:

PATTERN1
a
b
c
PATTERN2
d
e
f
PATTERN2
g
h

I want to print line between PATTERN1 and 2nd match of PATTERN2:

PATTERN1
a
b
c
PATTERN2
d
e
f
PATTERN2

Here's one way to do it with sed:

sed '/PATTERN1/,$!d;/PATTERN2/x;//x;q;;g;' infile

This just deletes all lines (if any) up to the first occurrence of PATTERN1 and then, on each line that matches PATTERN2 it exchanges buffers. If the new pattern space also matches, it means it's the 2nd occurrence so it exchanges back and quits (after auto-printing). If it doesn't match it means it's the 1st occurrence so it copies the hold space content over the pattern space via g (so now there's a line matching PATTERN2 in the hold buffer) and goes on...

and another way with awk:

awk '/PATTERN1/t=1; t==1print; if (/PATTERN2/)c++; c==2exit' infile

It starts printing and counting lines matching PATTERN2 only when encountering a line matching PATTERN1 and exits when counter reaches 2.

The right tool for this job is pcregrep:

pcregrep -M 'PATTERN1(.|n)*PATTERN2' file

where option -M allows pattern to match more than one line and (.|n)* match any character or newline zero or more times.

Notice that we took advantage of the greediness of the grep. If you would want to print form pattern1 up to the first occurrence of the pattern2, then non-greedy *? should be used instead of *.

As a generalization, to print up to the nth occurrence of PATTERN2:

pcregrep -M 'PATTERN1((.|n)*?PATTERN2)n' file

Change n to actual number you need.

Just use flags:

$ awk '/PATTERN1/flag=2;next flag; /PATTERN2/flag--' file
a
b
c
PATTERN2
d
e
f
PATTERN2

That is: when you find PATTERN1 set the flag to a positive value; in particular, 2. Then, when you find PATTERN2, decrease that flag in one. This way, it will exhaust after the second match. In between, use flag as a value that triggers the print $0 when it has a true value (2 or 1).

If we told regarding sed is to much easy to collect nesessary lines then print

sed -n '
 /PATTERN1/
 :1
 $!N
 /(PATTERN2).*1/!b1
 p
 
' file