How can I print source line number in Perl?

Question

Is it possible to get the current source line number in Perl? The equivalent in C++ is __LINE__.

I've used it to quickly track the progress through a very long process, and to check the order things are done in, like breakpoints but without using the debugger — David Sykes, Dec 15 '08 at 09:11
@LeonTimmermans: I am responding to your very old comment about why a Perl programmer might want _ _FILE_ _ and _ _ LINE _ _. Basically, the same reasons why a C/C++ programmer might want them. E.g. today I refactored a test so that Test::Differences::eq_or_diff was called in a subroutine. The line number reported was in the subroutine not where the subroutine was called from. Adding __ LINE __ to the test name helps me find the failing test. Now if I could just write a macro CODE_LOCATION in Perl5. — Krazy Glew, Nov 22 '15 at 21:42

score 64 · Accepted Answer · edited Oct 30 '22 at 11:34

64

The __LINE__ literal is documented in the Special Literals section of the perldata man page.

print "File: ", __FILE__, " Line: ", __LINE__, "\n";

or

warn("foo");

edited Oct 30 '22 at 11:34

mivk

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answered Dec 10 '08 at 09:01

Eugene Yokota

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Maybe I do bad google searches, though in 99.999% they are very precise for me. For this question I search with a sentence 'how to print current line in perl' basically, and I got only replies regards outputting the line number from the file read with `$.`, which is trivial as incrementing variable in a loop reading lines. So I wonder if many other people would not have the same issue. Interestingly enough, it seems as if Google put this question among search results once I searched for it differently, or I just overlooked it at my initial attempts. – FantomX1 Oct 19 '20 at 13:40

score 8 · Answer 2 · edited Oct 30 '22 at 19:12

8

Note there's a gotcha with

$ perl -e'warn("foo")'
foo at -e line 1.

If it ends with a newline it won't print the line number

$ perl -e'warn("foo\n")'
foo

This is documented in perldoc -f die, but is perhaps easy to miss in the perldoc -f warn section's reference to die.

edited Oct 30 '22 at 19:12

brian d foy

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answered Dec 11 '08 at 02:34

bigiain

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score 2 · Answer 3 · answered Oct 17 '14 at 22:28

"use Carp" and play with the various routines and you also get a stack - not sure if this way is better or worse than the "caller" method suggested by cnd. I have used the LINE and FILE variables (and probably other similar variables) in C and Perl to show where I got in the code and other information when debugging but have seen little value outside a debug environment.

score 2 · Answer 4 · edited Feb 26 '12 at 18:34

2

This prints out the line where you are, and also the "stack" (list of lines from the calling programs (scripts/modules/etc) that lead to the place you are now)

while(my @where=caller($frame++)) { print "$frame:" . join(",",@where) . "\n"; }

edited Feb 26 '12 at 18:34

sth

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answered Feb 26 '12 at 13:26

cnd

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How can I print source line number in Perl?

4 Answers4