relative paths

[John M. Dlugosz]

Background: I'm still working on my documentation system. I'm storing the database of cross references as href targets that are all relative to the output tree. A reference within one document should be a relative path to get to the target.

The Problem: Given two paths that are expressed relative to the same starting point, express the first as a relative path from the second.

Example, given a\b\c to a\b\d, return ..\d .

I'm sure I can figure this out easily enough, so I'm not asking anyone to do it for me. But sharing code that's already been tested is another story! Since there is abs2rel and other goodies in File::Spec, I'm wondering if there is already a function that does this somewhere, so I don't have to write one.

Anybody seen it?

—John

[japhy]

I tested this, and it seems to work:

sub relpath {
  my ($from, $to) = @_;
  my @f = split '/', $from;
  my @t = split '/', $to;

  while (@f and @t) {
    shift(@f), shift(@t), next if $f[0] eq $t[0];
    return join '/', ("..") x @f, @t;
  }

  return "./";
}

_____________________________________________________
Jeff[japhy]Pinyan: Perl, regex, and perl hacker.
s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;

[merlyn]

Since there is abs2rel and other goodies in File::Spec

abs2rel should be what you are using. Why is that function not suitable?

-- Randal L. Schwartz, Perl hacker

[John M. Dlugosz]

Because it never occured to me that it could hop between siblings (by inserting ..'s)—I thought it only trimmed off a root. I also don't know what it would do if given another relative path as the "current" parameter.

[clemburg]

Been there. For me, the main problem was how to use abs2rel() - somehow I think the calling convention is backwards.

Example:

sub make_relative_path_to_website {
    my ($file) = @_;
    return File::Spec::Unix->abs2rel($config->{START_DIR},
                                     File::Spec::Unix->rel2abs($file))
+;
}

Christian Lemburg
Brainbench MVP for Perl
http://www.brainbench.com