ln-s-relative.sh - Make a symlink in relative path form

ln-s-relative.sh

#!/bin/dash

set -u

ln_s_relative() {
  local root=""
  if [ $# -eq 3 ]; then
    local root="$1"; shift
  fi
  local target="$1"; shift
  local linkname="$1"; shift

  ## Refuse relative paths in arguments
  case "$target/$linkname" in
  .|..|./*|../*|*/./*|*/../*|*/.|*/..)
    echo "ln_s_relative: ERROR: Invalid argument" 1>&2
    return 1
    ;;
  esac
  if [ -n "${root##/*}" ] || [ -z "$target" ] || [ -n "${target##/*}" ] || [ -z "$linkname" ] || [ -n "${linkname##/*}" ]; then
    echo "ln_s_relative: ERROR: Invalid argument" 1>&2
    return 1
  fi

  if [ -d "$root$linkname" ]; then
    local dirname="$linkname"
  else
    local dirname=`/usr/bin/dirname "$linkname"`
  fi

  local root_from_linkname=`echo "$dirname" |/bin/sed 's#^/##;s#/$##;s#[^/][^/]*#..#g'`
  local target_relative="$root_from_linkname$target"

  [ "$dirname" = "/" ] && dirname=""
  /bin/ln -s "$target_relative" "$root$dirname/${linkname##*/}"
}

if [ $# -lt 2 ] || [ $# -gt 3 ]; then
  echo "Usage: $0 [ROOT] TARGET LINKNAME"
  exit 1
fi

ln_s_relative "$@"