标签：linux

在类Unix系统的Bash环境下，怎样检查文件是否存在呢？

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

文章翻译自：http://www.cyberciti.biz/faq/unix-linux-test-existence-of-file-in-bash/

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