test命令在shell脚本中的应用

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接触shell脚本后，发现test命令在脚本中的应用非常多。学习shell脚本test命令是必须要掌握的，而且他很容易被掌握。
test命令可以处理shell脚本的各类工作。它产生的不是一般的输出（文本内容等），而是可使用的退出状态（true和false）。test接受各种不同的参数，可控制它要执行哪一种测试。

test命令有两种模式：
第一种：可以通过man test查看：test [-OPTION] EXPRESSION
不带参数：

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if test "$str1 = $str2"
then
    ......
fi

带参数：

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if test -x "$file"
then
    ......
fi

第二种：[‘空’[-OPTION] EXPRESSION‘空’] 注意左右方括号和测试表达式之间必须存在一个空格.
不带参数：

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if [ "$str1 = $str2" ]
then 
    ......
fi

带参数：

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if [ -z "$str1" -a -z "$str2" ]
then 
    ......
fi

这两种只是格式不同，使用时情况因人而异。表达式的逻辑如下：
( EXPRESSION )
EXPRESSION is true

! EXPRESSION
EXPRESSION is false

表达式组合：
EXPRESSION1 -a EXPRESSION2
both EXPRESSION1 and EXPRESSION2 are true

EXPRESSION1 -o EXPRESSION2
either EXPRESSION1 or EXPRESSION2 is true

[-OPTION]参数如下（栽man test）：

       -n STRING
the length of STRING is nonzero

STRING equivalent to -n STRING

-z STRING
the length of STRING is zero

STRING1 = STRING2
the strings are equal

STRING1 != STRING2
the strings are not equal

INTEGER1 -eq INTEGER2
INTEGER1 is equal to INTEGER2

        INTEGER1 -ge INTEGER2
INTEGER1 is greater than or equal to INTEGER2

INTEGER1 -gt INTEGER2
INTEGER1 is greater than INTEGER2

INTEGER1 -le INTEGER2
INTEGER1 is less than or equal to INTEGER2

INTEGER1 -lt INTEGER2
INTEGER1 is less than INTEGER2

INTEGER1 -ne INTEGER2
INTEGER1 is not equal to INTEGER2

FILE1 -ef FILE2
             FILE1 and FILE2 have the same device and inode numbers

        FILE1 -nt FILE2
FILE1 is newer (modification date) than FILE2

FILE1 -ot FILE2
FILE1 is older than FILE2

-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

FROM: http://blog.chinaunix.net/uid-28728968-id-4407312.html

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