读书笔记之101个超酷脚本之001

今天无意中发现一本挺有意思的shell编程的书，是e文的，内容是101个shell案例，坚持明天看一个，写点心得。

下面是例子001：

#!/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 1
fi

checkForCmdInPath "$1"
case $? in
  0 ) echo "$1 found in PATH"                  ;;
  1 ) echo "$1 not found or not executable"    ;;
  2 ) echo "$1 not found in PATH"              ;;
esac

exit 0

这脚本目的是用来检测输入的选项$1是否在PATH中。
 

 

这脚本有几个地方值得注意的：

1）它运用了函数嵌套，在checkForCmdInPath里嵌套了in_path函数。

2）if [ "${var%${var#?}}" = "/" ]  这语句中的${var%${var#?}}是显示变量的第一个字符，也可以用${varname:1:1} 或$(echo $var | cut -c1)替代。

3） elif ! in_path $var $PATH ; then  这意思是如果in_path $var $PATH 执行结果不为0的话则

问题：

发现输入 echo ， echo_err， /etco_err 都返回正确结果，但输入 /etc/echo_right (存在着执行文件但不在PATH中)却返回found in PATH。我想这脚本还有需要完善的地方。

第一集over