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Re: command for relative path
From: |
Dmitry V. Levin |
Subject: |
Re: command for relative path |
Date: |
Sun, 13 Nov 2011 22:45:28 +0400 |
Hi,
On Sat, Nov 12, 2011 at 11:45:56AM -0700, Eric Blake wrote:
[...]
> http://docs.python.org/library/os.path.html
> >> os.path.relpath(path[, start])
> >>
> >> Return a relative filepath to path either from the current directory
> >> or from an optional start point.
>
> Ah, so the idea is that python has a function that computes a relative
> pathname to one path given a starting point:
>
> $ relpath /usr/bin /tmp
> ../usr/bin
> $ relpath /usr/bin /usr/share
> ../bin
Btw, there is an utility in freebsd ports called relpath:
http://www.freebsd.org/cgi/cvsweb.cgi/ports/sysutils/relpath/
ftp://ftp.freebsd.org/pub/FreeBSD/ports/local-distfiles/beech/relpath-0.1.0.tar.gz
$ lftp -c 'cat
http://www.freebsd.org/cgi/cvsweb.cgi/~checkout~/ports/sysutils/relpath/pkg-descr'
Usage: relpath [-d DIR] START_DIR END_PATH
Find a relative path from START_DIR to END_PATH.
Prints the relative path on standard out.
If -d DIR, then only emit a relative path if both
START_DIR and END_PATH are sub-directories of DIR;
otherwise, emit an absolute path to END_PATH.
> This seems like you could do it in shell without resorting to python, by
> computing a canonical name for both the destination and the starting
> point, then comparing common prefixes, and for every directory component
> that differs after the common prefix, replacing the directory with
> '../'. This has been done before; for example, this is from gnulib-tool:
>
> # func_relativize DIR1 DIR2
> # computes a relative pathname RELDIR such that DIR1/RELDIR = DIR2.
> # Input:
> # - DIR1 relative pathname, relative to the current directory
> # - DIR2 relative pathname, relative to the current directory
> # Output:
> # - reldir relative pathname of DIR2, relative to DIR1
> func_relativize ()
> {
> dir0=`pwd`
> dir1="$1"
> dir2="$2"
> sed_first='s,^\([^/]*\)/.*$,\1,'
> sed_rest='s,^[^/]*/*,,'
> sed_last='s,^.*/\([^/]*\)$,\1,'
> sed_butlast='s,/*[^/]*$,,'
> while test -n "$dir1"; do
> first=`echo "$dir1" | sed -e "$sed_first"`
> if test "$first" != "."; then
> if test "$first" = ".."; then
> dir2=`echo "$dir0" | sed -e "$sed_last"`/"$dir2"
> dir0=`echo "$dir0" | sed -e "$sed_butlast"`
> else
> first2=`echo "$dir2" | sed -e "$sed_first"`
> if test "$first2" = "$first"; then
> dir2=`echo "$dir2" | sed -e "$sed_rest"`
> else
> dir2="../$dir2"
> fi
> dir0="$dir0"/"$first"
> fi
> fi
> dir1=`echo "$dir1" | sed -e "$sed_rest"`
> done
> reldir="$dir2"
> }
>
> Doing it in fewer processes seems possible with something like a single
> awk script, although I haven't tried writing one; at any rate, awk would
> be more portable than python for the same task.
>
> But yes, providing this as an alternative mode of coreutils' realpath
> instead of scripting it in shell or awk seems like a useful addition -
> would you care to submit a patch?
AFAIR the coreutils' realpath is called readlink. ;)
Would "readlink --relative" or something like this be a good choice?
Or should it rather be a new utility?
--
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Re: command for relative path, Peng Yu, 2011/11/13