#!perl -w
use strict;

while (<DATA>) {
	chomp;
	print "current line=$_\n";
	if (/check next/) {
		my $pos = tell();
		my $testline = <DATA>;
		chomp $testline;
		print "'next line' = $testline\n";
		#do something...
		seek DATA, $pos, 0;
	}
	print "current line=$_\n";
}

__DATA__
line 1
line 2
line 3 check next
line 4 OK?
line 5