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