which

#!/bin/sh ## which(1) written in pure POSIX shell.

## A `which` utility is *not* included in the POSIX standard.
## This version upports -s (silent) and -a (all), and -v (verbose).

## (c) 2015 Geoff Nixon. Public Domain; no warranty expressed or implied.

which(){
  which_try=
  which_result=
  which_verbose=0
  which_silent=0

  which_usage(){ echo "usage: "$(basename "$0")" [-asv] program ..." >&2 ;}

  which_error(){
    [ $which_verbose = 1 ] &&
      echo "$(basename "$0"): no $which_util in ($PATH)" >&2 || :
  }

  OPTIND=1; while getopts "ahsv?" which_opt; do
      case "$which_opt" in
        a) which_next=continue ;;
        h) which_usage; exit 0 ;;
        s) which_silent=1      ;;
        v) which_verbose=1     ;;
       \?) which_usage; exit 1 ;;
      esac
  done
  shift $((OPTIND - 1))

  which_try(){
    echo "$PATH" | tr ':' '\n' | while read which_component; do
      which_try="$which_component/$which_util"
      [ -x "$which_try" ] && echo "$which_try" && break
    done
  }

  for which_util; do :; done

  [ -z "$which_util" ] && which_usage && exit 1

  which_result="$(which_try "$which_util")"

  [ -z "$which_result" ] && which_error && exit 1 ||
    [ $which_silent = 1 ] && exit 0 || echo "$which_result" | uniq
}

which "$@"