Appropriate use of white space is one of the most important things that you can do to improve program legibility.

use strict;
use warnings;

print "Which Metric jaccard or Bleu:";
my $metric=<>;
chomp $metric;

print "Which source title or snippet or url:";
my $source=<>;
chomp $source;

if($metric eq "jaccard")
{
    if($source eq "title")
    {
        print "in title";
        system("/usr/bin/perl filecom.pl")
    }
    elsif($source eq "snippet")
    {
        print "in snippet";
        system("/usr/bin/perl searchsnipdup.pl")
    }
    elsif($source eq "url")
    {
        print "in url";
        print"jaccard method not called";
    }
    else
    {
        print "jacccard not called";
    } 
}
elsif($metric eq "bleu")
{
    print "bleu called";
}
else
{
    print "bleu not called";
}
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