sed & awk

sedawkunixtext-processingmultilinepattern-space

Abstraction: Advanced sed multiline pattern space commands N, P, D for complex text transformations

Key points:

Three multiline commands: N (append next input line to pattern space), P (print first line of pattern space), D (delete first line and restart)
N differs from n: lowercase n outputs current pattern space before reading next line; N appends without outputting
Match embedded newlines with \n in regex; insert newline in replacement using backslash followed by literal newline (not \n)
Classic use case: match a phrase split across two lines by reading next line into pattern space then substituting across the embedded newline
D command removes only the first line of pattern space and passes remainder back to top of script, enabling a sliding-window processing loop
N/P/D combination: output current line (P), remove it (D), next iteration processes formerly-second line as current

Connections: Sed · Text Processing · Unix Tools