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

本文出自 “你就当我是浮夸吧” 博客,请务必保留此出处http://2804976.blog.51cto.com/2794976/588675

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