#!perl -w
use strict;

while (<DATA>) {
    s!\s+$!!;
    if( m!\btimescale\b! ) {
        print "Found timescale in [$_]\n";
    } else {
        print "Ignored line [$_]\n";
    };
};

__DATA__
===============================================
// 1st commented line
//second commented line 
// timescale 1ns /5 ns
 
timescale 1ns/4ns  //this comment should also be ignored

module modulename1 (a b c )

some lines.... 
some lines ...


//third commented line 
//fourth commented line 

timescale 3ns/5ns
module modulename2 (p q r)

some lines ...

//fifth comment
//timescale 4ns/5ns

timescale 1ns/3ns 

module modulename3 (m n p )

some line ...

================================================