高级人 - AI

目录不存在,则创建之,写法如下

if [ ! -x /Users/XXX/Desktop/temp/ ];
    then
    mkdir /Users/XXX/Desktop/temp/
fi

注意if后面,[之前要有空格!,注意if语句行尾的;,还有then,结束if的配对符号fi.

 #!/bin/sh 

 myPath="/var/log/httpd/" 
 myFile="/var /log/httpd/access

 # 这里的-x 参数判断$myPath是否存在并且是否具有可执行权限 
 if [ ! -x "$myPath"]; then 
 mkdir "$myPath" 
 fi 

 # 这里的-d 参数判断$myPath是否存在 
 if [ ! -d "$myPath"]; then 
 mkdir "$myPath" 
 fi 

 # 这里的-f参数判断$myFile是否存在 
 if [ ! -f "$myFile" ]; then 
 touch "$myFile" 
 fi 

 # 其他参数还有-n,-n是判断一个变量是否是否有值 
 if [ ! -n "$myVar" ]; then 
 echo "$myVar is empty" 
 exit 0 
 fi 

 # 两个变量判断是否相等 
 if [ "$var1" = "$var2" ]; then 
 echo '$var1 eq $var2' 
 else 
 echo '$var1 not eq $var2' 
 fi 

Conditional Logic on Files

-a file exists. 
-b file exists and is a block special file. 
-c file exists and is a character special file. 
-d file exists and is a directory. 
-e file exists (just the same as -a). 
-f file exists and is a regular file. 
-g file exists and has its setgid(2) bit set. 
-G file exists and has the same group ID as this process. 
-k file exists and has its sticky bit set. 
-L file exists and is a symbolic link. 
-n string length is not zero. 
-o Named option is set on. 
-O file exists and is owned by the user ID of this process. 
-p file exists and is a first in, first out (FIFO) special file or 
named pipe. 
-r file exists and is readable by the current process. 
-s file exists and has a size greater than zero. 
-S file exists and is a socket. 
-t file descriptor number fildes is open and associated with a 
terminal device. 
-u file exists and has its setuid(2) bit set. 
-w file exists and is writable by the current process. 
-x file exists and is executable by the current process. 
-z string length is zero. 

shell比较两个字符串是否相等的办法是：

if [ "$test"x = "test"x ]; then

这里的关键有几点：

• 使用单个等号
• 注意到等号两边各有一个空格：这是unix shell的要求
• 注意到"$test"x最后的x，这是特意安排的，因为当$test为空的时候，上面的表达式就变成了x = testx，显然是不相等的。而如果没有这个x，表达式就会报错：[: =: unary operator expected

{$var%?}

#!/bin/bash
echo $@
for i in $@; do
    echo $i
done

单引号

str='this is a string' 单引号字符串的限制：

• 单引号里的任何字符都会原样输出，单引号字符串中的变量是无效的
• 单引号字串中不能出现单引号（对单引号使用转义符后也不行）

  双引号

your_name='qinjx'
str="Hello, I know your are \"$your_name\"! \n"

• 双引号里可以有变量
• 双引号里可以出现转义字符