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前言
大家在工作的时候可能经常会遇到这样的需求，在类Unix系统的Bash环境下，怎样检查文件是否存在呢？既然有需求，当然就有解决的办法了，Shell中的test命令，可以用来检测文件的类型或者比较数值是否相等，该命令也能用来检查文件是否存在。
可以用如下的命令来进行检查：
test -e filename [ -e filename ] test -f filename [ -f filename ]
下面的命令，则使用Shell的条件表达式，判断/etc/hosts文件是否存在：
[ -f /etc/hosts ] && echo "Found" || echo "Not found"
该组合命令会输出以下内容：
Found
更常见的用法，则是将test命令放置在if..else..fi条件判断的条件表达式，然后在其中写上不同的分支逻辑
#!/bin/bash file="/etc/hosts" if [ -f "$file" ] then echo "$file found." else echo "$file not found." fi
检测文件属性的相关操作符
如果文件存在，并且具有相应的属性，如下的操作符都会返回true：
-b FILE
FILE exists and is block special
-c FILE
FILE exists and is character special
-d FILE
FILE exists and is a directory
-e FILE
FILE exists
-f FILE
FILE exists and is a regular file
-g FILE
FILE exists and is set-group-ID
-G FILE
FILE exists and is owned by the effective group ID
-h FILE
FILE exists and is a symbolic link (same as -L)
-k FILE
FILE exists and has its sticky bit set
-L FILE
FILE exists and is a symbolic link (same as -h)
-O FILE
FILE exists and is owned by the effective user ID
-p FILE
FILE exists and is a named pipe
-r FILE
FILE exists and read permission is granted
-s FILE
FILE exists and has a size greater than zero
-S FILE
FILE exists and is a socket
-t FD file descriptor FD is opened on a terminal
-u FILE
FILE exists and its set-user-ID bit is set
-w FILE
FILE exists and write permission is granted
-x FILE
FILE exists and execute (or search) permission is granted
以上命令，从man test复制而来。
使用上述符号的方法一模一样：
if [ operator FileName ] then echo "FileName - Found, take some action here" else echo "FileName - Not found, take some action here" fi
总结
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