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 position of the nth recurring occurence of a specific character.
ie perl script.pl "," 3 "|" data.txt
would replace every 3rd,6th,9th…etc comma with a pipe.

So if data.txt had the following before the script was run:

fd,3232,gfd67gf,
peas,989767,jkdfnfgjhf,
dhdhjsk,267,ujfdsy,fuyds,637296,ldosi,fduy,
873,fuisouyd,try
save,2837,ipoi

It should then have this after the script was run:

fd,3232,gfd67gf|
peas,989767,jkdfnfgjhf|
dhdhjsk,267,ujfdsy|fuyds,637296,ldosi|fduy,
873,fuisouyd|try
save,2837,ipoi

Answer 1

Small perl hack to solve the problem. Using the index function to find the commas, modulus to replace the right one, and substr to perform the replacement.

use strict;
use warnings;

while (<>) {
    my $x=index($_,","); 
    my $i = 0; 
    while ($x != -1) {
        $i++; 
        unless ($i % 3) { 
            $_ = substr($_,0,$x) ."|". substr($_,$x+1); 
        }
        $x = index($_,",",$x + 1) 
    } 
    print;
}

Run with perl script.pl file.csv.

Note: You can place the declaration my $i before the while(<>) loop in order to do a global count, instead of a separate count for each line. Not quite sure I understood your question in that regard.