How can I suppress empty leading fields in Perl's split()?

Question

The perlfunc entry for split says:

By default, empty leading fields are preserved

Hinting that there's a way to over-ride that default, but later on all it says is:

Empty leading fields are produced when there are positive-width matches at the beginning of the string

...does this mean that there's no way to skip that first field?

It's not mission-critical, but I'm splitting a root-relative URL, say /foo/bar/, on the slashes and getting

['', 'foo', 'bar']

and wondering if there's a way to not get that blank first item.

Answer 1

I would imagine you could just drop all "/" at the beginning of your URL.

Answer 2

If you are splitting via the separator of '/' then I see that there is nothing wrong with the output. Considering the first character is a deliminator then it has no choice but to have a empty string.

Answer 3

One approach you could use is to use a regexp to remove any leading delimeters.

e.g.

$str = "/foo/bar";
$str =~ m!^/*!!;

Then do your split as before.

Answer 4

If you want to split up path elements, look at File::Spec or Path::Class, which handle all of the operating system specific stuff:

 use File::Spec;

 my( $root, @path_parts ) = File::Spec->splitdir( $path );

The nice thing about keeping the root is that you can go backward easily and still keep that leading slash (or whatever your opearting system might use):

 my $path = File::Spec->catfile( $root, @path_parts );

This isn't such a big deal with URLs since they all use a unix-like path specification. Still, it's easy to construct the local path in the same way, and remember where the root is (which may be important on Windows, VMS, etc):

 my ($docroot_root, @doc_root ) = File::Spec->splitdir( $ENV{DOCUMENT_ROOT} );
 my $local_path = File::Spec->catfile( $docroot_root, @doc_root, @path_parts );

Otherwise, you're stuck with what split does. It assumes that you care about the position of fields, so it preserves their position (i.e. the thing before the first separator is always position 0 in the list, even if it is empty). For your problem, I tend to write it as a list assignment where I use a variable to soak up the initial empty field, just like I'd do with

 my( $root, @path_parts ) = split m|/|, $path;

Answer 5

split(' ', $string) will split the string on spaces but not give you leading, trailing or internal empty fields.

I thought this was a more general case, but doing a split on 'x' is equivalent to /x/

Answer 6

You can use grep to remove any fields that are zero-length.

grep (length, split ('/','/foo/bar'))

I don't think split can do what you want on it's own.

The people who are telling you to use a domain-specific function to do your splitting are correct. Domain specific split equivalents will automatically handle various non-obvious special cases for you.

Answer 7

like this

(undef,@x)= split /\//,$string;

Answer 8

brian d foy mentioned the File::Spec module. I really like this since it takes a intuitive approach and you know exactly what you are getting.

Depending on your scripting/programming style with Perl, you might want to try:

($volume, $directories, $file) = File::Spec->splitpath( $path );

The result is straightforward and if you need the volume for example, it's right at your fingertips!

And it makes your code a lot more readable! Just be careful, different modules have different specs regarding, for example, symbolic links or mounted disks.