如何在像操作系统一样在Unix下运行的bash中测试文本文件是否存在？
您需要使用test命令检查文件类型并比较值。
可以使用同一命令查看文件是否不存在。
语法如下：

test -e filename
[ -e filename ]
 
test -f filename
[ -f filename ]

以下命令将使用bash条件执行来判断是否存在一个名为/etc/hosts的文本文件：

[ -f /etc/hosts ] && echo "Found" || echo "Not found"

输出示例：

Found

可以将相同的代码转换为与if..else..fi结合使用，从而可以根据测试命令的成功或者失败进行选择：

#!/bin/bash
file="/etc/hosts"
if [ -f "$file" ]
then
	echo "$file found."
else
	echo "$file not found."
fi

文件测试操作符

如果文件存在，则以下运算符返回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

语法相同：

if [ operator FileName ]
then
     echo "FileName - Found, take some action here"
else
   echo "FileName - Not found, take some action here"
fi