一元运算符预期 [英] unary operator expected

问题描述

我一直试图弄清楚什么是错与此，但就是无法弄清楚..

这是部分似乎得到一个错误。

 的elif [$操作=人];然后
    如果[$ AUG1 =添加];然后＃＆LT;  -  75号线
    回声手册页：加上
    回声
    回声语法：加[数字1] [2号]
    回声
    回声简介：
    回声添加两个不同的数字加在一起。
    回声
    回声信息：
    回声中新增V1.0
    回声
ELIF [-z $ AUG1]。然后
    回声请指定一个命令来阅读man page。
其他
    回声有该命令没有手册页。
科幻
 

我得到这个错误：

  calc_1.2：75行：[：=：一元运算符预期
 

解决方案

如果你知道你总是要使用bash，它更容易为始终使用双支架有条件的复合命令 [。 ..] ，而不是符合POSIX标准的单支架版本 [...] 。在 [...] 复合，字的拆分和路径扩展不会应用到的话，那么你可以依靠

 如果[[$ AUG1 ==和]];
 

到 $ AUG1 的值与字符串比较和。

如果您使用 [...] ，你总是需要记住翻一番这样的引用变量：

 如果[$ AUG1=和];
 

如果你不引用变量扩展和变量未定义或空的，它从犯罪现场消失了，只留下

 如果[=和];
 

这不是有效的语法。 （这也将失败，不同的​​错误消息，如果 $ AUG1 包含空格或shell转义字符。）

现代 [经营者有很多其他不错的功能，包括常规的前pression匹配。

I've been trying to figure out whats wrong with this but just can't figure it out..

This is the part seems to be getting an error..

elif [ $operation = "man" ]; then
    if [ $aug1 = "add" ]; then         # <- Line 75
    echo "Man Page for: add"
    echo ""
    echo "Syntax: add [number 1] [number 2]"
    echo ""
    echo "Description:"
    echo "Add two different numbers together."
    echo ""
    echo "Info:"
    echo "Added in v1.0"
    echo ""
elif [ -z $aug1 ]; then
    echo "Please specify a command to read the man page."
else
    echo "There is no manual page for that command."
fi

I get this error:

calc_1.2: line 75: [: =: unary operator expected

解决方案

If you know you're always going to use bash, it's much easier to always use the double bracket conditional compound command [[ ... ]], instead of the Posix-compatible single bracket version [ ... ]. Inside a [[ ... ]] compound, word-splitting and pathname expansion are not applied to words, so you can rely on

if [[ $aug1 == "and" ]];

to compare the value of $aug1 with the string and.

If you use [ ... ], you always need to remember to double quote variables like this:

if [ "$aug1" = "and" ];

If you don't quote the variable expansion and the variable is undefined or empty, it vanishes from the scene of the crime, leaving only

if [ = "and" ]; 

which is not a valid syntax. (It would also fail with a different error message if $aug1 included white space or shell metacharacters.)

The modern [[ operator has lots of other nice features, including regular expression matching.

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