shell脚本编程基础--``与''符号的区分

一失足成千古恨，再回头已百年神！！！！！Fuck

在shell脚本编程时，编写统计当前目录下的文件数，小小的错误竟然出现在一个符号上，``与''符号的区分:

#!bin/sh
counter=0
for files in *                    # 替换符*表明对当前目录中所有文件循环

do

    counter=`expr $counter + 1`   #  expr：对表达式求值的命令

done                         # let counter=$counter+1

echo "There are $counter files in `pwd` we need to process"

运行结果是：

[root@localhost shell实验]# ls
hello.c  hello.sh  hi.sh  s2  s3  s4  s5  s6  s7  s8
[root@localhost shell实验]# sh s8
There are 10 files in /home/shell实验 we need to process

 

#!bin/sh
counter=0
for files in *                    # 替换符*表明对当前目录中所有文件循环

do

    counter='expr $counter + 1'   #  expr：对表达式求值的命令

done                         # let counter=$counter+1

echo "There are $counter files in `pwd` we need to process"

运行结果是：

[root@localhost shell实验]# sh s8
There are expr $counter + 1 files in /home/shell实验 we need to process

 

所以：

counter='expr $counter + 1' ，'' 单撇号不是对counter的运算，只是对counter简单的替换

counter=`expr $counter + 1`，``才是能够进行counter运算