How to Calculate a Relative Path from Two Absolute Paths in Linux Shell?

Assuming GNU coreutils:

• For symlinks, ln has recently learned the --relative option.

• For everything else, realpath supports options --relative-to= and --relative-base=.

For me, this answer (which uses a python oneliner) works perfect.

$ python -c "import os.path; print os.path.relpath('/a/d/e.txt', '/a/b/c')"
../../d/e.txt

Tested successfully on linux (Kubuntu 14.04) an on Mac OSX, needs Python 2.6.

To not depend on realpath that is not consistently available and minimize the dependencies, I came up with this (using a little help from this answer):

function relative_path_from_to() {
  # strip trailing slashes
  path1=${1%\/}
  path2=${2%\/}
  # common part of both paths
  common=$(printf '%s\x0%s' "${path1}" "${path2}" | sed 's/\(.*\/\).*\x0\1.*/\1/')
  # how many directories we have to go up to the common part
  up=$(grep -o "/" <<< ${path1#$common} | wc -l)
  # create a prefix in the form of ../../ ...
  prefix=""; for ((i=0; i<=$up; i++)); do prefix="$prefix../"; done
  # return prefix plus second path without common
  printf "$prefix${2#$common}"
}

Spawns a subshell for finding the common part of both pathes. I hope you like it - works for me.