#!/usr/bin/perl

# http://perlmonks.org/?node_id=1190410

use strict;
use warnings;

my $input = <<END;
|   |   |   |   |   |   |   |   !   !
first line
\t\tsecond line
\t\t\tthird line
\tfourth line
\t\tfifth line
\t\tline with\t\tin the middle
last line
END

open my $fh, '<', \$input or die "$! opening file";
while(<$fh>)
  {
  s/\G\t/    /g;
  print;
  }