我要评论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。
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