perl - replace every nth (and multiples) occurrences of a character with another character

Question

Does anyone know any unix commands/perl script that would insert a specific character (that can be entered as either hex (ie 7C) or as the actual character (ie |)) in the po

Answer 1

This processes the input file one line at a time (no slurping :)
For hex input, just pass '\x7C' or whatever, as $1

#!/bin/bash  

b="${1:-,}"                             # the "before" field delimiter 
n="${2:-3}"                             # the number of fields in a group
a="${3:-|}"; [[ $a == [\|] ]] && a='\|' # the "after" group delimiter

sed -nr "x;G; /(([^$b]+$b){$((n-1))}[^$b]+)$b/{s//\1$a/g}
         s/.*\n//; h; /.*$a/{s///; x}; p" input_file

---

Here it is again, with some comments.

sed -nr "x;G    # pat = hold + pat
  /(([^$b]+$b){$((n-1))}[^$b]+)$b/{s//\1$a/g}
  s/.*\n//      # del fields from prev line
  h             # hold = mod*\n
  /.*$a/{ s///  #  pat = unmodified
          x     # hold = unmodified, pat = mod*\n
        }            
  p             # print line"  input_file