如何在if语句中表示多个条件？

素颜马尾好姑娘i 2022-11-29 05:46 137阅读 0赞

本文翻译自：[How to represent multiple conditions in a shell if statement?][How to represent multiple conditions in a shell if statement]

*I want to represent multiple conditions like this:* **我想代表多个条件，例如：**

if [ ( $g -eq 1 -a "$c" = "123" ) -o ( $g -eq 2 -a "$c" = "456" ) ]   
    then  
        echo abc;  
    else  
        echo efg;   
    fi

*but when I execute the script, it shows* **但是当我执行脚本时，它显示**

syntax error at line 15: `[' unexpected,

*where line 15 is the one showing if ....* **第15行显示的是....**

*What is wrong with this condition?* **这种情况怎么了？** *I guess something is wrong with the `()` .* **我猜想`()` 。**

--------------------

### \#1楼 ###

参考：[https://stackoom.com/question/g3qx/如何在if语句中表示多个条件][https_stackoom.com_question_g3qx_if]

--------------------

### \#2楼 ###

*Be careful if you have spaces in your string variables and you check for existence.* **如果字符串变量中有空格并检查是否存在，请格外小心。** *Be sure to quote them properly.* **确保正确引用它们。**

if [ ! "${somepath}" ] || [ ! "${otherstring}" ] || [ ! "${barstring}" ] ; then

--------------------

### \#3楼 ###

*Using `/bin/bash` the following will work:* **使用`/bin/bash`可以正常工作：**

if [ "$option" = "Y" ] || [ "$option" = "y" ]; then
        echo "Entered $option"
    fi

--------------------

### \#4楼 ###

*Classic technique (escape metacharacters):* **经典技术（转义元字符）：**

if [ $ "$g" -eq 1 -a "$c" = "123" $ -o $ "$g" -eq 2 -a "$c" = "456" $ ]
    then echo abc
    else echo efg
    fi

*I've enclosed the references to `$g` in double quotes;* **我已将对`$g`的引用括在双引号中；** *that's good practice, in general.* **一般来说，这是一个好习惯。** *Strictly, the parentheses aren't needed because the precedence of `-a` and `-o` makes it correct even without them.* **严格来说，不需要括号，因为`-a`和`-o`的优先级使得即使没有它们也正确。**

*Note that the `-a` and `-o` operators are part of the POSIX specification for [`test`][test] , aka `[` , mainly for backwards compatibility (since they were a part of `test` in 7th Edition UNIX, for example), but they are explicitly marked as 'obsolescent' by POSIX.* **请注意， `-a`和`-o`运营商的POSIX规范的一部分[`test`][test] ，又名`[` ，主要用于向后兼容性（因为他们的部分`test`在第7版UNIX等），但它们被明确标记为“过时由POSIX。** *Bash (see [conditional expressions][] ) seems to preempt the classic and POSIX meanings for `-a` and `-o` with its own alternative operators that take arguments.* **Bash（请参阅[条件表达式][conditional expressions] ）似乎以其自己的带参数的替代运算符抢占了`-a`和`-o`的经典含义和POSIX含义。**

--------------------

*With some care, you can use the more modern `[[` operator, but be aware that the versions in Bash and Korn Shell (for example) need not be identical.* **一定要小心，您可以使用更现代的`[[`运算符，但是请注意，例如Bash和Korn Shell中的版本不必相同。**

for g in 1 2 3
    do
        for c in 123 456 789
        do
            if [[ ( "$g" -eq 1 && "$c" = "123" ) || ( "$g" -eq 2 && "$c" = "456" ) ]]
            then echo "g = $g; c = $c; true"
            else echo "g = $g; c = $c; false"
            fi
        done
    done

*Example run, using Bash 3.2.57 on Mac OS X:* **在Mac OS X上使用Bash 3.2.57运行示例：**

g = 1; c = 123; true
    g = 1; c = 456; false
    g = 1; c = 789; false
    g = 2; c = 123; false
    g = 2; c = 456; true
    g = 2; c = 789; false
    g = 3; c = 123; false
    g = 3; c = 456; false
    g = 3; c = 789; false

*You don't need to quote the variables in `[[` as you do with `[` because it is not a separate command in the same way that `[` is.* **你并不需要引用变量`[[`如同你`[`因为它不是一个单独的命令，在同样的方式， `[`是。**

--------------------

> *Isn't it a classic question?* **这不是一个经典的问题吗？**

*I would have thought so.* **我会这么想的。** *However, there is another alternative, namely:* **但是，还有另一种选择，即：**

if [ "$g" -eq 1 -a "$c" = "123" ] || [ "$g" -eq 2 -a "$c" = "456" ]
    then echo abc
    else echo efg
    fi

*Indeed, if you read the 'portable shell' guidelines for the `autoconf` tool or related packages, this notation — using ' `||`* **确实，如果您阅读了`autoconf`工具或相关软件包的“便携式外壳”指南，则使用- `||`表示。** *' and ' `&&` ' — is what they recommend.* **'和' `&&` '—是他们的建议。** *I suppose you could even go so far as:* **我想您甚至可以做到：**

if [ "$g" -eq 1 ] && [ "$c" = "123" ]
    then echo abc
    elif [ "$g" -eq 2 ] && [ "$c" = "456" ]
    then echo abc
    else echo efg
    fi

*Where the actions are as trivial as echoing, this isn't bad.* **在动作像回声一样琐碎的情况下，这还不错。** *When the action block to be repeated is multiple lines, the repetition is too painful and one of the earlier versions is preferable — or you need to wrap the actions into a function that is invoked in the different `then` blocks.* **当要重复执行的动作块为多行时，重复会很痛苦，并且较早的版本之一是可取的-否则您需要将动作包装到在不同的`then`块中调用的函数中。**

--------------------

### \#5楼 ###

在Bash中：

if [[ ( $g == 1 && $c == 123 ) || ( $g == 2 && $c == 456 ) ]]

--------------------

### \#6楼 ###

$ g=3
    $ c=133
    $ ([ "$g$c" = "1123" ] || [ "$g$c" = "2456" ]) && echo "abc" || echo "efg"
    efg
    $ g=1
    $ c=123
    $ ([ "$g$c" = "1123" ] || [ "$g$c" = "2456" ]) && echo "abc" || echo "efg"
    abc

[How to represent multiple conditions in a shell if statement]: https://oldbug.net/q/g3qx/How-to-represent-multiple-conditions-in-a-shell-if-statement
[https_stackoom.com_question_g3qx_if]: https://stackoom.com/question/g3qx/%E5%A6%82%E4%BD%95%E5%9C%A8if%E8%AF%AD%E5%8F%A5%E4%B8%AD%E8%A1%A8%E7%A4%BA%E5%A4%9A%E4%B8%AA%E6%9D%A1%E4%BB%B6
[test]: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/test.html
[conditional expressions]: http://www.gnu.org/software/bash/manual/bash.html#Bash-Conditional-Expressions