用来检测输入的选项$1是否在PATH中的shell脚本

#!/bin/sh# inpath - Verifies that a specified program is either valid as is,#  or that it can be found in the PATH directory list.in_path(){ # Given a command and the PATH, try to find the command. Returns # 0 if found and executable, 1 if not. Note that this temporarily modifies # the IFS (input field separator) but restores it upon completion. cmd=$1    path=$2     retval=1 oldIFS=$IFS  IFS=":" for directory in $path do  if [ -x $directory/$cmd ] ; then   retval=0   # if we're here, we found $cmd in $directory  fi done IFS=$oldIFS return $retval}checkForCmdInPath(){ var=$1 # The variable slicing notation in the following conditional # needs some explanation: ${var#expr} returns everything after # the match for 'expr' in the variable value (if any), and # ${var%expr} returns everything that doesn't match (in this # case, just the very first character. You can also do this in # Bash with ${var:0:1}, and you could use cut too: cut -c1. if [ "$var" != "" ] ; then  if [ "${var%${var#?}}" = "/" ] ; then   if [ ! -x $var ] ; then    return 1   fi  elif ! in_path $var $PATH ; then   return 2  fi fi} if [ $# -ne 1 ] ; then echo "Usage: $0 command" >&2 ; exit 1ficheckForCmdInPath "$1"case $? in 0 ) echo "$1 found in PATH"         ;; 1 ) echo "$1 not found or not executable"  ;; 2 ) echo "$1 not found in PATH"       ;;esacexit 0