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#!/bin/sh
#
# Get the relative path to $target from $source
#
# Credits:
# [1] Getting relative links between two paths
# http://unix.stackexchange.com/a/85068
# [2] Convert absolute path into relative path given a current directory using Bash
# http://stackoverflow.com/a/12498485
#
#
# Aaron LI
# Created: 2015-01-06
# Updated: 2015-01-06
#
relpath() {
# both $1 and $2 are absolute paths beginning with /
# $1 must be a canonical path; that is none of its directory
# components may be ".", ".." or a symbolic link
#
# returns relative path to $2/$target from $1/$source
source=$1
target=$2
common_part=$source
result=
while [ "${target#"$common_part"}" = "$target" ]; do
# no match, means that candidate common part is not correct
# go up one level (reduce common part)
common_part=$(dirname "$common_part")
# and record that we went back, with correct / handling
if [ -z "$result" ]; then
result=..
else
result=../$result
fi
done
if [ "$common_part" = / ]; then
# special case for root (no common path)
result=$result/
fi
# since we now have identified the common part,
# compute the non-common part
forward_part=${target#"$common_part"}
# and now stick all parts together
if [ -n "$result" ] && [ -n "$forward_part" ]; then
result=$result$forward_part
elif [ -n "$forward_part" ]; then
# extra slash removal
result=${forward_part#?}
fi
printf '%s\n' "$result"
}
if [ $# -ne 2 ]; then
echo "Usage:"
echo " `basename $0` <source> <target>"
exit 1
fi
relpath "$1" "$2"
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