Learning Perl, 5th Edition

Using Simple Modules

Suppose that you’ve got a long filename like /usr/local/bin/perl in your program, and you need to find out the basename. That’s easy enough, since the basename is everything after the last slash (it’s just perl in this case):

my $name = "/usr/local/bin/perl";
(my $basename = $name) =~ s#.*/##;  # Oops!

As you saw earlier, first Perl will do the assignment inside the parentheses, then it will do the substitution. The substitution is supposed to replace any string ending with a slash (that is, the directory name portion) with an empty string, leaving just the basename.

And if you try this, it seems to work. Well, it seems to, but actually, there are three problems.

First, a Unix file or directory name could contain a newline character. (It’s not something that’s likely to happen by accident, but it’s permitted.) So, since the regular expression dot (.) can’t match a newline, a filename like the string "/home/fred/flintstone\n/brontosaurus" won’t work right—that code would think the basename is "flintstone\n/brontosaurus". You could fix that with the /s option to the pattern (if you remembered about this subtle and infrequent case), making the substitution look like this: s#.*/##s. The second problem is that this is Unix-specific. It assumes that the forward slash will always be the directory separator, as it is on Unix, and not the backslash or colon that some systems use.

And the third (and biggest) problem with this is that we’re trying to solve a problem that someone ...