（转） 判断文件是否存在的shell脚本代码

转载地址：http://www.jb51.net/article/34330.htm 
-f 和-e的区别 
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. 
是用 -s 还是用 -f 这个区别是很大的！ 
实例代码：

#!/bin/sh
# 判断文件是否存在
# link：www.jb51.net
# date：2013/2/28  
 myPath="/var/log/httpd/"
myFile="/var /log/httpd/access.log" 
 # 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