In that case, you can use $. (perldoc perlvar) to know what line you are in. For example:

#!/usr/bin/perl

while (<DATA>) {
        print $. . ": $_";
}

__DATA__
a
b
c
d
e
f
g
h
i

# Would display when run...

$ ./test.pl
1: a
2: b
3: c
4: d
5: e
6: f
7: g
8: h
9: i
[download]

Cheers,
KM