SED: addressing two lines before match

Question

Print line, which is situated 2 lines before the match(pattern).

I tried next:

sed -n \': loop
/.*/h
:x
{n;n;/cen/p;}
s/./c/p
t x
s/n/c/p
t loop
{g;p         


        

Answer 1

The script:

  sed -n "1N;2N;/XXX[^\n]*$/P;N;D"

works as follows:

• Read the first three lines into the pattern space, 1N;2N
• Search for the test string XXX anywhere in the last line, and if found print the first line of the pattern space, P
• Append the next line input to pattern space, N
• Delete first line from pattern space and restart cycle without any new read, D, noting that 1N;2N is no longer applicable