You may be talking about line numbers in a text editor used to edit Perl scripts. If that's the case, you're asking a broad question because we have no idea what code editor you're using (and since it's not a Perl topic we probably don't much care).

Or you may be asking how to determine what line number you've just read out of a file. If that's the case, the "$." special variable will tell you what line number you're reading. See perlvar for details.

Or you may be asking how to determine what line in your script is currently executing. If that's the case, the __LINE__ tag will tell you. You can print __LINE__, "\n";, for example. See perldata for details about the __LINE__ "Special Literal".

Or if you just want to know how many lines there are in a file.... well, here's a Perl solution:

perl -n -e "END { print $., "\n"; }" file.txt
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