Numbering lines matching the pattern using sed

Question

I\'m writing the script that searches for lines that match some pattern. I must use sed for this script. This works fine for searching and printing matched lines:

Answer 1

Switch to awk.

BEGIN {
  ln=0
}

$0 ~ m {
  ln+=1
  print ln " " $0
  next
}

{
  print $0
}

...

awk -f script.awk -v m='' < input.txt