Hi, let's suppose we have tab-separated data like that in the lines after the __DATA__ token and we want to swap columns two and three:

use strict;
use warnings;

while (<DATA>) {    # go through data line by line
    chomp;          # don't forget to remove newline character
    my @fields = split /\t+/;
    print join "\t",           # join fields with tab
          @fields[ 0, 2, 1 ],  # select fields using array slice
          "\n";
}

__DATA__
Col1    Col2    Col3
a       b       c
1       2       3
[download]

To work with files, just

• add $^I = ".bak"; before the while loop to edit files in place keeping backups
• replace <DATA> with <> (diamond operator)

and then run the program like this:

$ perl script.pl *.dat
[download]