abs2rel - convert an absolute path to a relative path

- NAME
- SYNOPSIS
- DESCRIPTION
- BUGS
- LIMITATIONS
- AUTHORS

# NAME

abs2rel - convert an absolute path to a relative path

rel2abs - convert a relative path to an absolute path

realpath - convert a logical path to a physical path (resolve symlinks)

splitpath - split a path in to volume, directory and filename components

joinpath - join volume, directory, and filename components to form a path

splitdirs - split directory specification in to component names

joindirs - join component names in to a directory specification

setfstype - set the file system type

# SYNOPSIS

        use File::PathConvert qw(realpath abs2rel rel2abs setfstype splitpath
          joinpath splitdirs joindirs $resolved);

        $relpath = abs2rel($abspath);
        $abspath = abs2rel($abspath, $base);

        $abspath = rel2abs($relpath);
        $abspath = rel2abs($relpath, $base);

        $path = realpath($logpath) || die "resolution stopped at $resolved";

        ( $volume, $directory, $filename )= splitpath( $path ) ;
        ( $volume, $directory, $filename )= splitpath( $path, 'nofile' ) ;

        $path= joinpath( $volume, $directory, $filename ) ;

        @directories= splitdirs( $directory ) ;
        $directory= joindirs( @directories ) ;

# DESCRIPTION

File::PathConvert provides functions to convert between absolute and relative paths, and from logical paths to physical paths on a variety of filesystems, including the URL 'filesystem'.

Paths are decomposed internally in to volume, directory, and, sometimes filename portions as appropriate to the operation and filesystem, then recombined. This preserves the volume and filename portions so that they may be returned, and prevents them from interfering with the path conversions.

Here are some examples of path decomposition. A '****' in a column indicates the column is not used in abs2rel and rel2abs functions for that filesystem type.

        FS      VOLUME                  Directory       filename
        ======= ======================= =============== =============
        URL     http:                   /a/b/           c?query
                http://fubar.com        /a/b/           c?query
                //p.d.q.com             /a/b/c/         ?query

        VMS     Server::Volume:         [a.b]           c
                Server"access spec"::   [a.b]           c
                Volume:                 [a.b]           c

        Win32   A:                      \a\b\c          ****
                \\server\Volume         \a\b\c          ****
                \\server\Volume         \a/b/c          ****

        Unix    ****                    \a\b\c          ****

        MacOS   Volume::                a:b:c           ****

Many more examples abound in the test.pl included with this module.

Only the VMS and URL filesystems indicate if the last name in a path is a directory or file. For other filesystems, all non-volume names are assumed to be directory names. For URLs, the last name in a path is assumed to be a filename unless it ends in '/'.

Other assumptions are made as well, especially MacOS and VMS. THESE MAY CHANGE BASED ON PROGRAMMER FEEDBACK!

The conversion routines abs2rel, rel2abs, and realpath are the main focus of this package. splitpath and joinpath are provided to allow volume oriented filesystems (almost anything non-unixian, actually) to be accomodated. splitdirs and joindirs provide directory path grammar parsing and encoding, which is especially useful for VMS.

setfstype
  This is called automatically on module load to set the filesystem type according to $^O. The user can call this later set the filesystem type manually. If the name is not recognized, unix defaults are used. Names matching /^URL$/i, /^VMS$/i, /^MacOS$/i, or /^(ms)?(win|dos)/32|nt)?$/i yield the appropriate (hopefully) filesystem settings. These strings may be generalized in the future.

  Examples:

          File::PathConvert::setfstype( 'url' ) ;
          File::PathConvert::setfstype( 'Win32' ) ;
          File::PathConvert::setfstype( 'HAL9000' ) ; # Results in Unix default

abs2rel
  abs2rel converts an absolute path name to a relative path: converting /1/2/3/a/b/c relative to /1/2/3 returns a/b/c

          $relpath= abs2rel( $abspath ) ;
          $relpath= abs2rel( $abspath, $base ) ;

  If `$abspath` is already relative, it is returned unchanged. Otherwise the relative path from `$base` to `$abspath` is returned. If `$base` is undefined the current directory is used.

  The volume and filename portions of `$base` are ignored if present. If `$abspath` and `$base` are on different volumes, the volume from `$abspath` is used.

  No filesystem calls are made except for getting the current working directory if `$base` is undefined, so symbolic links are not checked for or resolved, and no check is done for existance.

  Examples

          # Unix
          'a/b/c' == abs2rel( 'a/b/c', $anything )
          'a/b/c' == abs2rel( '/1/2/3/a/b/c', '/1/2/3' )

          # DOS
          'a\\b/c' == abs2rel( 'a\\b/c', $anything )
          'a\\b/c' == abs2rel( '/1\\2/3/a\\b/c', '/1/2/3' )

          # URL
          'http:a/b/c'           == abs2rel( 'http:a/b/c', $anything )
          'http:a/b/c'           == abs2rel( 'http:/1/2/3/a/b/c',
                                             'ftp://t.org/1/2/3/?z' )
          'http:a/b/c?q'         == abs2rel( 'http:/1/2/3/a/b/c/?q',
                                             'ftp://t.org/1/2/3?z'  )
          'http://s.com/a/b/c?q' == abs2rel( 'http://s.com/1/2/3/a/b/c?q',
                                             'ftp://t.org/1/2/3/?z')

rel2abs
  rel2abs makes converts a relative path name to an absolute path: converting a/b/c relative to /1/2/3 returns /1/2/3/a/b/c.

          $abspath= rel2abs( $relpath ) ;
          $abspath= rel2abs( $relpath, $base ) ;

  If `$relpath` is already absolute, it is returned unchanged. Otherwise `$relpath` is taken to be relative to `$base` and the resulting absolute path is returned. If `$base` is not supplied, the current working directory is used.

  The volume portion of `$relpath` is ignored. The filename portion of `$base` is also ignored. The volume from `$base` is returned if present. The filename portion of `$abspath` is returned if present.

  No filesystem calls are made except for getting the current working directory if `$base` is undefined, so symbolic links are not checked for or resolved, and no check is done for existance.

  Examples

          # Unix
          '/a/b/c'       == rel2abs( '/a/b/c', $anything )
          '/1/2/3/a/b/c' == rel2abs( 'a/b/c', '/1/2/3' )

          # DOS
          '\\a\\b/c'                == rel2abs( '\\a\\b/c', $anything )
          '/1\\2/3\\a\\b/c'         == rel2abs( 'a\\b/c', '/1\\2/3' )
          'C:/1\\2/3\\a\\b/c'       == rel2abs( 'D:a\\b/c', 'C:/1\\2/3' )
          '\\\\s\\v/1\\2/3\\a\\b/c' == rel2abs( 'D:a\\b/c', '\\\\s\\v/1\\2/3' )

          # URL
          'http:/a/b/c?q'            == rel2abs( 'http:/a/b/c?q', $anything )
          'ftp://t.org/1/2/3/a/b/c?q'== rel2abs( 'http:a/b/c?q',
                                                 'ftp://t.org/1/2/3?z' )

realpath
  realpath makes a canonicalized absolute pathname and resolves all symbolic links, extra ``/'' characters, and references to /./ and /../ in the path. realpath resolves both absolute and relative paths. It returns the resolved name on success, otherwise it returns undef and sets the valiable `$File::PathConvert::resolved` to the pathname that caused the problem.

  All but the last component of the path must exist.

  This implementation is based on 4.4BSD `realpath(3).` It is not tested under other operating systems at this time.

  If '/sys' is a symbolic link to '/usr/src/sys':

          chdir('/usr');
          '/usr/src/sys/kern' == realpath('../sys/kern');
          '/usr/src/sys/kern' == realpath('/sys/kern');

splitpath
  To be written...

joinpath
  To be written...

splitdirs
  To be written...

joindirs

# BUGS

realpath is not fully multiplatform.

# LIMITATIONS

- In URLs, paths not ending in '/' are split such that the last name in the path is a filename. This is not intuitive: many people use such URLs for directories, and most servers send a redirect. This may cause programers using this package to code in bugs, it may be more pragmatic to always assume all names are directory names. (Note that the query portion is always part of the filename).

- If the relative and base paths are on different volumes, no error is returned. A silent, hopefully reasonable assumption is made.

- No detection of unix style paths is done when other filesystems are selected, like File::Basename does.

# AUTHORS

Barrie Slaymaker Shigio Yamaguchi