ln-srf

#!/bin/sh
#
# Author: Carlos Santos <unixmania@gmail.com>
# This file is in public domain.
#

error() {
	echo "$@" 1>&2
	exit 1
}

src="$1"
dst="$2"

check_path() {
	case "$2" in
		*/../*|*/./*|*/.|*/..) error "$1 path '$2' must be absolute";;
		*/) error "$1 path '$2' must not end with '/'";;
		/?*) ;;
		*) error "$1 path '$2' must start with '/'";;
	esac
}

check_path "source" "$src"
check_path "destination" "$dst"

# strip leading '/'
src=${src#/*}
tmp=${dst#/*}

s_prefix=${src%%/*}
d_prefix=${tmp%%/*}

# strip leading common
while [ "$s_prefix" = "$d_prefix" ]; do
	src="${src#$s_prefix/}"
	tmp="${tmp#$d_prefix/}"
	s_prefix=${src%%/*}
	d_prefix=${tmp%%/*}
done

s_prefix="../"
while [ -n "$d_prefix" ] && [ "$tmp" != "$d_prefix" ]; do
	s_prefix="../$s_prefix"
	tmp="${tmp#$d_prefix/}"
	d_prefix=${tmp%%/*}
done

ln -s -f "$s_prefix$src" "$dst"