A Bash script providing a command for computing relative path between two filesystem paths

relpath.bash

#!/bin/bash
# relpath -- Compute relative path from a given DIR to given PATHs
# Usage: relpath DIR PATH...
# 
# Example: relpath /a/b/c /a/d/e/f
#  prints: ../../d/e/f
# 
# Example: relpath /a/b/c /
#  prints: ../../../
# 
# Example: relpath /a/b/c /a/b/c/g/h
#  prints: g/h

# lovingly stolen from https://gist.github.com/1573996
relpath() {
  local from="$1" to="$2"
  from=${from//\/\//\/}
  from=${from%/}
  IFS=/
  dirs=(${from#/})
  for to; do
    to=${to//\/\//\/}
    to=${to%/}
    local commonPrefix=/ d=
    for d in "${dirs[@]}"; do
      case "$to/" in "$commonPrefix$d/"*) ;;
        *) break;;
      esac
      commonPrefix+="$d/"
    done
    local ancestor="${from#${commonPrefix%/}}"
    ancestor=${ancestor//[^\/]/}
    ancestor=${ancestor//\//..\/}
  done
  echo "$ancestor${to#$commonPrefix}"
}


relpath "$@"