a script I use with claws-mail: https://bit.ly/2JJs5ql

side-by-side-diff.pl

#!/usr/bin/perl
use strict;
use warnings;
use File::Copy qw(copy);
#use X11::Protocol;

my $fname = $ARGV[0];
if(not defined $fname) {
	die "No input\n";
}

my $dir =  $ENV{"HOME"}."\/\.claws-mail\/my-custom-scripts\/tmp\/";
if (-d $dir) {
	print "Directory $dir found. OK.\n";
} else {
	print "Creating directory $dir.\n";
	unless (mkdir $dir) {
		die "Failed to create directory $dir.\n";
	}
}

my $additions, my $deletions;
$additions = $dir."additions.txt";
$deletions = $dir."deletions.txt";

open(my $fh, '<', $fname) or die "Couldn't open file: $fname: $!\n";
open(my $fh_add, '>', $additions) or die "Couldn't open file $additions: $!\n";
open(my $fh_del, '>', $deletions) or die "Couldn't open file $deletions: $!\n";
while(!eof($fh)) {
	defined(my $line = readline $fh) or die "Failed to read line.\n";
	if ($line =~ m/^\+[^++]/) {
		print $fh_add "$line";
		print $fh_del "\n";
	} elsif ($line =~m/^\-[^--]/) {
		print $fh_add "\n";
		print $fh_del "$line";
	} else {
		print $fh_add "$line";
		print $fh_del "$line";
	}
}
close($fh_del);
close($fh_add);
close($fh);
#my $x = X11::Protocol->new();
#print $x->{screens}->[0]->{width_in_pixels} .
#	  'x' .
#	  $x->{screens}->[0]->{height_in_pixels} .
#	  "\n";
#my $w = 0.5 * $x->{screens}->[0]->{width_in_pixels};
#my $h = 0.5 * $x->{screens}->[0]->{height_in_pixels};
#my $geometry = "$w"."x"."$h"."+0+0";
my $command = qq[/usr/bin/icdiff --whole-file --cols=150 -H $deletions $additions | gvim - -c ":AnsiEsc" &];
system($command);
#my @cmd = ('/usr/bin/uxterm');
#push @cmd, '-geometry';
#push @cmd, $geometry;
#push @cmd, '-l';
#push @cmd, '-maximized';
#push @cmd, '-hold';
#push @cmd, '-e';
#push @cmd, $command;
#system(@cmd);