#!/usr/local/bin/perl

open (IN, "/text.txt");
while (<IN>){
	if ($_ =~ /hello/){
		# do what ever
	}
}
close IN;

##</code><code>##

#!/usr/local/bin/perl

open (IN, "/text.txt");
@lines = (IN);
close (IN);
foreach (@lines){
	if ($_ =~ /hello world/){
		# do what ever
	}
}