Perl dropping " at line xxx" from warnings when "\n" is present

bprew has asked for the wisdom of the Perl Monks concerning the following question:

Why does perl omit the "at line xxx" when I supply a "\n" at the end of a warning?
Example:

b3n@sdf:~> cat test.pl
#!/usr/bin/perl

warn "foo";

warn "bar\n";
b3n@sdf:~> perl test.pl
foo at test.pl line 3.
bar
[download]

This appears to be the same for both perl 5.6.0 (eww) and 5.8.7 (specifically perl, v5.8.7 built for alpha-netbsd-thread-multi)

Is this to allow for exception handling with objects or something similar? I'm assuming this is expected behaviour, but I didn't see any note of it in the warn() perldoc page. I won't lose any sleep over it, but it did strike me as odd.
Thanks
Update: added perl version(s)

--
Ben
"Naked I came from my mother's womb, and naked I will depart."

Comment on Perl dropping " at line xxx" from warnings when "\n" is present Download Code

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Re: Perl dropping " at line xxx" from warnings when "\n" is present by friedo (Prior) on Dec 09, 2005 at 19:07 UTC
It's a feature. die works the same way, e.g. `perl -e 'die "foo"' perl -e 'die "foo\n"'` [download] It's useful if you want to report a warning or fatal error to a user as opposed to a programmer, since a user woudldn't care about scary line-numbers and such. It doesn't affect passing exception objects, since if you're passing an object do `die` you won't be passing a string that could contain "\n".	[reply] [d/l] [select]
Re: Perl dropping " at line xxx" from warnings when "\n" is present by ww (Archbishop) on Dec 09, 2005 at 19:10 UTC
ummm -- bad man page! down, man page. sit! ActiveState has no such omission: `perldoc -f warn` and `perldoc -f die` As noted above, warn's doc offers a strong indication that one should also read re die... where, in the ~~second~~ corrected third paragraph one finds: `If the last element of LIST does not end in a newline, the current script line number and input line number (if any) are also printed, and a newline is supplied....` [download] which clearly implies that there's something different about the behavior when `\n` is present.	[reply] [d/l] [select]
Re: Perl dropping " at line xxx" from warnings when "\n" is present by ikegami (Patriarch) on Dec 09, 2005 at 19:09 UTC
It's a simple way of giving the programmer the option of including the line number in the message or not. It is indirectly mentioned ("just like die") in warn's documentation.	[reply]
Re: Perl dropping " at line xxx" from warnings when "\n" is present by Fletch (Bishop) on Dec 09, 2005 at 19:12 UTC
If you look at the docs for die it says: If the last element of LIST does not end in a newline, the current script line number and input line number (if any) are also printed, and a newline is supplied. And warn says "Produces a message on STDERR just like "die", but doesn't exit or throw an exception." Granted that's not explicitly saying "`warn` will print the current script line number and input line number unless the message ends with a newline". You might submit a documentation patch to p5p adding something like "(see the documentation for `C<die>` for more details)."	[reply] [d/l] [select]
Re^2: Perl dropping " at line xxx" from warnings when "\n" is present by bprew (Monk) on Dec 09, 2005 at 19:18 UTC
Don't I feel sheepish :) Thanks for pointing me in the right direction, next time when it says just like 'xxx', I'll got ahead and read the docs for 'xxx' -- Ben "Naked I came from my mother's womb, and naked I will depart."	[reply]