Your sample could perhaps be better written using a __DATA__ section as:

use strict;

#looked variable
my $VarString = 'C++';

print "Start...\n";

#search string
while (<DATA>) {
    #check with the matching expression
    next unless m/$VarString/;
   
    chomp;
    print "I have found the string $VarString at line $.\n";

}

print "Stop\n";

__DATA__
VISUAL BASIC,PERL,PASCAL
C#,C,C++
ASSEMBLER,PHP,JAVA
HTML,XML,JAVA
[download]

but the major issue is the old problem of reinventing tricky wheels. CSV, in general, is tricky to parse correctly. You are much better to use something like Text::CSV.