use strict;
use warnings;
use Tie::File;


my $file_name = 'test.txt';
my @name;
tie @name, 'Tie::File' ,$file_name;
die "error!!!" unless defined (my $pid_1 = fork());
 exit search_string(0,9999,"8888") unless ($pid_1);
die "error!!!" unless defined (my $pid_2 = fork());
exit search_string(10000,19999,"18888") unless ($pid_2);
die "error!!!" unless defined (my $pid_3 = fork());
exit search_string(20000,29999,"28888") unless ($pid_3);
wait;
wait;
wait;
untie @name;
sub search_string {
	my ($from,$to,$string) = @_;
	for ($from .. $to) {
		print "the $_ th line of test.txt is $string\n" if $name[$_] =~ /^$string$/x;
	}
}

__test.txt__
1
2
3
...
29998
29999
30000

##</code><code>##

# first time
the 8887 th line of test.txt is 8888
the 18887 th line of test.txt is 18888
the 28888 th line of test.txt is 28888

#second time
the 8888 th line of test.txt is 8888
the 18888 th line of test.txt is 18888
the 28889 th line of test.txt is 28888

#third time
the 8887 th line of test.txt is 8888
the 28887 th line of test.txt is 28888
Use of uninitialized value in pattern match (m//) at serarch_file.pl line 42, <$
fh> line 29884.
Use of uninitialized value in pattern match (m//) at serarch_file.pl line 42, <$
fh> line 29884.
Use of uninitialized value in pattern match (m//) at serarch_file.pl line 42, <$
fh> line 29884.
Use of uninitialized value in pattern match (m//) at serarch_file.pl line 42, <$
fh> line 29884.
Use of uninitialized value in pattern match (m//) at serarch_file.pl line 42, <$
fh> line 29884.