How can I print source line number in Perl?

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

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

warn("foo");

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...

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