use strict;
use warnings;
use Text::CSV;

my( $infile, $outfile, @cols ) = @ARGV;
print "Reading from $infile.\n";
print "Writing to $outfile.\n";
print "Target columns are @cols.\n";

open my $in,  "<", $infile  or die "Cannot open $infile: $!\n";
open my $out, ">", $outfile or die "Cannot open $outfile: $!\n";
$_-- for @cols; # correct column numbering

my $csv   = Text::CSV->new( );
my $pipe  = Text::CSV->new( { sep_char => '|' } );
my $tilde = Text::CSV->new( { sep_char => '~', eol => "\n" } );

while( my $line = $csv->getline( $in ) ) {
		$pipe ->combine( @$line );
		$tilde->combine( @$line[@cols], $pipe->string );
		print $out $tilde->string;
}

close $out;
close $in;