>>619
perlsynのいちばん最後のほう。

Plain Old Comments (Not!)

Perl can process line directives, much like the C preprocessor. Using this, one can control Perl's idea of filenames
and line numbers in error or warning messages (especially for strings that are processed with "eval()"). The syntax
for this mechanism is the same as for most C preprocessors: it matches the regular expression

# example: '# line 42 "new_filename.plx"'
/^\# \s*
line \s+ (\d+) \s*
(?:\s("?)([^"]+)\2)? \s*
$/x

with $1 being the line number for the next line, and $3 being the optional filename (specified with or without
quotes).