exists/scripts/exists.hsh

#!/usr/bin/hsh
# Bourne shell function for finding executable files in the $PATH
# Intended for legacy shells such as hsh or osh

# Copyright 2017 orbea
# All rights reserved.
#
# Redistribution and use of this script, with or without modification, is
# permitted provided that the following conditions are met:
#
# 1. Redistributions of this script must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
#
#  THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR IMPLIED
#  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
#  MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO
#  EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
#  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
#  PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
#  OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
#  WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
#  OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
#  ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

exists () {
  v=1
  while [ "$#" -gt 0 ]; do
    arg="$1"; shift
    case "$arg" in ''|*/) continue ;; esac
    x="`printf %s "$arg" | cut -d '/' -f 2-`"
    z="`printf %s "$arg" | cut -d '/' -f 1`"
    [ ! -f "$z/$x" ] || [ ! -x "$z/$x" ] && [ "$z/$x" = "$arg" ] && continue
    [ "$x" = "$z" ] && [ -x "$z/$x" ] && [ ! -f "$arg" ] && z=
    p=":$z:$PATH"
    while [ "$p" != "`printf %s "$p" | cut -d ':' -f 1`" ]; do
      p="`printf %s "$p" | cut -d ':' -f 2-`"
      d="`printf %s "$p" | cut -d ':' -f 1`"
      [ -f "$d/$x" ] && [ -x "$d/$x" ] && printf %s\\n "$d/$x" && v=0 && break
    done
  done
  return "$v"
}

exists "$@"