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#!/bin/sh
# POSIX shell implementation of `realpath --relative-to=$1 $2.
# This is an adaptation of the implementation from
# <https://github.com/Offirmo/offirmo-shell-lib>.
# returns relative path to $2=$target from $1=$source
## NOTE : path are compared in text only. They don’t have to exist
## and they WONT be normalized/escaped
## Result in "$return_value"# both $1 and $2 are absolute paths beginning with /
src="$1"
target="$2"
common_part="$src"
result=""
while test "${target#$common_part}" = "${target}" ; do
#echo "common_part is now : \"$common_part\""
#echo "result is now : \"$result\""
#echo "target#common_part : \"${target#$common_part}\""
# no match, means that candidate common part is not correct
# go up one level (reduce common part)
common_part="$(dirname "$common_part")"
# and record that we went back
if test -z "$result" ; then
result=".."
else
result="../$result"
fi
done
#echo "common_part is : \"$common_part\""
if test "$common_part" = "/" ; then
# special case for root (no common path)
result="$result/"
fi
# since we now have identified the common part,
# compute the non-common part
forward_part="${target#$common_part}"
#echo "forward_part = \"$forward_part\""
if test -n "$result" && test -n "$forward_part" ; then
#echo "(simple concat)"
result="$result$forward_part"
elif test -n "$forward_part" ; then
#echo "(concat with slash removal)"
result="$(printf "%s" "$forward_part" | cut -c 1-)"
fi
printf "%s" "$result"
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