Try this:

#!/usr/bin/perl -l

use File::Spec;

my $file = "$mall_path/keywords/$filename";

print "Checking " . File::Spec->rel2abs($file);

if (-e $file) 
{ 
    #file exists - set variable and other things
}
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Update: Urg, too much Java earlier today. Changed + to . in print statement. Thanks shenme.