File, relative path handling.

[Hugh Sasse Staff Elec Eng]

Before I attempt to re-invent this wheel:
Has anyone come up with a method for converting an absolute
filesystem path into a relative path, given the path to relate to?
Pruning off the front is relatively easy, but handling '../'
correctly is likely to be error prone. Given that I need to cope
with Ruby 1.6 and 1.8 at the moment, and I will need to do something
graceful if the paths are on different Windows drives, well, I
suspect someone has run into this before me.

I need relative paths so I can move between data sets for testing
and between machines as well.

Thank you,
Hugh

[Warren Brown]

Hugh,

> Has anyone come up with a method for converting
> an absolute filesystem path into a relative
> path, given the path to relate to?

Well, this doesn't handle Windows drive letters, but it handles the
rest:

# Convert the given absolute path into a path
# relative to the second given absolute path.
def relativepath(abspath,relativeto)
path = abspath.split(File::SEPARATOR)
rel = relativeto.split(File::SEPARATOR)
while (path.length > 0) && (path.first == rel.first)
path.shift
rel.shift
end
('..' + File::SEPARATOR) * (rel.length - 1) + path.join(File::SEPARATOR)
end

I hope this helps.

- Warren Brown

[Sean O'Dell]

Hugh Sasse Staff Elec Eng wrote:

> Before I attempt to re-invent this wheel:
> Has anyone come up with a method for converting an absolute
> filesystem path into a relative path, given the path to relate to?
> Pruning off the front is relatively easy, but handling '../'
> correctly is likely to be error prone. Given that I need to cope
> with Ruby 1.6 and 1.8 at the moment, and I will need to do something
> graceful if the paths are on different Windows drives, well, I
> suspect someone has run into this before me.
>
> I need relative paths so I can move between data sets for testing
> and between machines as well.

Strange you should ask. I just wrote one of these and was about to port
it, and some other string utilities, to a C extension object.

It's brutal, but it works. Feel free to Rubify, anyone:

class String
public
def relative_path(topath)
frompath = self.clone
topath = topath.clone

fromdir = frompath.slice(/^.*?\//)
while(fromdir and frompath.slice(/^.*?\//) == topath.slice(/^.*?\//))
topath.slice!(/^.*?\//)
fromdir = frompath.slice!(/^.*?\//)
end

fromdir = frompath.slice!(/^.*?\//)
while(fromdir)
topath = "../" + topath
fromdir = frompath.slice!(/^.*?\//)
end

return topath
end

def relative_path!(topath)
self.replace(relative_path(topath))
end
end


Sean O'Dell

[Sean O'Dell]

Warren Brown wrote:

> Hugh,
>
>

>>Has anyone come up with a method for converting
>>an absolute filesystem path into a relative
>>path, given the path to relate to?

>
>
> Well, this doesn't handle Windows drive letters, but it handles the
> rest:
>
> # Convert the given absolute path into a path
> # relative to the second given absolute path.
> def relativepath(abspath,relativeto)
> path = abspath.split(File::SEPARATOR)
> rel = relativeto.split(File::SEPARATOR)
> while (path.length > 0) && (path.first == rel.first)
> path.shift
> rel.shift
> end
> ('..' + File::SEPARATOR) * (rel.length - 1) + path.join(File::SEPARATOR)
> end

Your relative path routine is MUCH more efficient than mine, geez. I
still don't "think" with everything Ruby has to offer. I'm still too
much of a "got-no-libs" C/C++ person. =)

Sean O'Dell

[Robert Klemme]

I suggest to put that on the Wiki - if it's not already there.

robert

"Warren Brown" <wkb@airmail.net> schrieb im Newsbeitrag
news:002001c3762a$36d81260$803888cf@warrenpc...

> Hugh,
>

> > Has anyone come up with a method for converting
> > an absolute filesystem path into a relative
> > path, given the path to relate to?

>
> Well, this doesn't handle Windows drive letters, but it handles the
> rest:
>
> # Convert the given absolute path into a path
> # relative to the second given absolute path.
> def relativepath(abspath,relativeto)
> path = abspath.split(File::SEPARATOR)
> rel = relativeto.split(File::SEPARATOR)
> while (path.length > 0) && (path.first == rel.first)
> path.shift
> rel.shift
> end
> ('..' + File::SEPARATOR) * (rel.length - 1) +

path.join(File::SEPARATOR)

> end
>
> I hope this helps.
>
> - Warren Brown
>
>

[Hugh Sasse Staff Elec Eng]

On Tue, 9 Sep 2003, Robert Klemme wrote:

>
> I suggest to put that on the Wiki - if it's not already there.
>
> robert

Oh! I seem to have missed this mssage [RubyTalk:81378], but these
often arrive out of sequence. This is a nice solution, and since at
the moment I'm keeping all the stuff on the same drive I can live
without the drive letter for now. This is much more elegant a
solution that I would have created. Thank you.

>
> "Warren Brown" <wkb@airmail.net> schrieb im Newsbeitrag
> news:002001c3762a$36d81260$803888cf@warrenpc...

[elided for brevity]

Thank you,
Hugh