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Home > Archive > Unix Shell > October 2005 > How to compute the relative path from the absolute paths?(in bash)
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How to compute the relative path from the absolute paths?(in bash)
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| PengYu.UT@gmail.com 2005-10-28, 4:53 pm |
| Hi,
Suppose I know the absolute paths of two directories? How can I compute
the simplest relative path between them?
/home/dir1/b
/home/dir1/c
I want the relative path of b to c is
.../b not ../../dir1/b, etc
Thanks,
Peng
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| William 2005-10-28, 4:53 pm |
| <PengYu.UT@gmail.com> wrote in message
news:1130512627.131217.130650@f14g2000cwb.googlegroups.com...
> Hi,
>
> Suppose I know the absolute paths of two directories? How can I compute
> the simplest relative path between them?
>
> /home/dir1/b
> /home/dir1/c
>
> I want the relative path of b to c is
> ../b not ../../dir1/b, etc
Just replace all the common path elements with
a single '..' element. How you do it depends on
your shell and which tools you want to use.
In bourne shell you could set IFS to '/', then
use set, shift and a for loop to compare each
element until you find a difference.
Once you find the difference, you replace
everything up to that point with ../ and add
all the leftover elements from your target
path string.
-Wm
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| William 2005-10-28, 4:53 pm |
| "William" <Reply@NewsGroup.Please> wrote in message
news:vtKdnTin2ahp2P_enZ2dnUVZ_s2dnZ2d@gi
ganews.com...
> <PengYu.UT@gmail.com> wrote in message
> news:1130512627.131217.130650@f14g2000cwb.googlegroups.com...
>
> Just replace all the common path elements with
> a single '..' element. How you do it depends on
> your shell and which tools you want to use.
>
> In bourne shell you could set IFS to '/', then
> use set, shift and a for loop to compare each
> element until you find a difference.
>
> Once you find the difference, you replace
> everything up to that point with ../ and add
> all the leftover elements from your target
> path string.
Here's a sample (could use some input validation,
and you might want to restore IFS, etc.):
#!/bin/sh
# Wanted: Relative path from mainPath to target path
mainPath="/etc/dir1/dir2/dir3/b"
target="/etc/dir1/dir2/dir4/c"
relPath=''
IFS='/'
set -- $target
for elem in $mainPath
do
case "$relPath" in
"")
[ "$1" = "$elem" ] || relPath="../$1"
;;
*)
relPath="$relPath/$1"
;;
esac
shift
done
echo "relPath = $relPath"
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| Alexis Huxley 2005-10-28, 4:53 pm |
| > Suppose I know the absolute paths of two directories? How can I compute
> the simplest relative path between them?
>
> /home/dir1/b
> /home/dir1/c
>
> I want the relative path of b to c is
> ../b not ../../dir1/b, etc
I have a function to do exactly that. You should be able to see what
you can strip. Not sure this is simplest - the code got patched and
patched and patched over years. Note that, as in your example, the
paths supplied are absolute.
ade_fnm_getrelativity()
{
# Usage: path_from <src_dir> <dst_dir>
# Desc: calculates a relative path from <src_dir> to <dst_dir>
local SRC_DIR DST_DIR SRC_LIST DIR REL_PATH DST_LIST
SRC_DIR=$1
DST_DIR=$2
ade_msg_debug 60 "ade_fnm_getrelativity: original paths $SRC_DIR and $DST_DIR"
{ expr $SRC_DIR : '\/' > /dev/null && expr $DST_DIR : '\/' > /dev/null; } || ade_msg_internalerror "Usage: ade_fnm_getrelativity <abspath> <abspath> (SRC_DIR=$SRC_DIR, DST_DIR=$DST_DIR)"
SRC_DIR=`echo $SRC_DIR | sed 's/^\///'`
DST_DIR=`echo $DST_DIR | sed 's/^\///'`
ade_msg_debug 60 "ade_fnm_getrelativity: leading slash removed paths $SRC_DIR and $DST_DIR"
SRC_LIST=`echo $SRC_DIR | sed 's/\// /g'`
for DIR in $SRC_LIST; do
ade_msg_debug 60 "ade_fnm_getrelativity: checking if paths start with $DIR ..."
expr $DST_DIR : "$DIR/" > /dev/null || expr $DST_DIR : "$DIR\$" > /dev/null || break
SRC_DIR=`echo $SRC_DIR | sed "s/^\\\\($DIR\\\\/\\\\|$DIR\\\$\\\\)//"`
DST_DIR=`echo $DST_DIR | sed "s/^\\\\($DIR\\\\/\\\\|$DIR\\\$\\\\)//"`
done
ade_msg_debug 60 "ade_fnm_getrelativity: reduced paths are '$SRC_DIR' and '$DST_DIR'"
if [ "X$SRC_DIR" = X -a "X$DST_DIR" = X ]; then
REL_PATH=.
else
REL_PATH=`echo $SRC_DIR | sed 's/[^/][^/]*/../g'`/$DST_DIR
fi
ade_msg_debug 60 "ade_fnm_getrelativity: returning $REL_PATH"
echo $REL_PATH
return 0
}
HTH
Alexis
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