在bash脚本中使用条件检查字符串参数 [英] use conditional in bash script to check string argument

问题描述

我正在尝试编写我的shell脚本 thing.sh ，以便在使其成为可执行文件并以单个字母"A"运行它后，如下所示:

I am trying to write my shell script thing.sh so that upon making it an executable and running it with the single letter ``A" like so:

$ ./thing.sh A

我得到了输出

A 

如果参数1不是A，则需要输出

If argument 1 is not A, I want the output

Not A 

到目前为止，这是我的代码:

Here is my code so far :

#!/bin/bash

if [ "$1" -eq "A"]
then echo "A"
else echo "Not A"
fi 

无论输入什么，都会返回

which returns, no matter what I enter,

./thing.sh: line 3: [:missing `]'
Not A

我正在尝试我希望用一个或几个字母检查的东西并将其与字母A进行比较；有人可以告诉我要使它正常工作我缺少什么吗?谢谢

I am trying what I hoped would check something with one or several letters and compare it against the letter A; could someone tell me what I am missing to get this to work? Thank you

推荐答案

简短一点:

#!/bin/bash

[[ $1 == A ]] && echo "A" || echo "not A"

?

和初学者版本(相同的逻辑):

And a beginner version (identical logic) :

#!/bin/bash

if [[ $1 == A ]]; then
    echo "A"
else
    echo "not A"
fi

就像Scott所说的那样，您遇到语法错误(缺少空格).

Like Scott said, you have a syntax error (missing space).

• 我在这里使用布尔逻辑. [[$ $ == A]] ，然后执行，如果为真，则执行 echo"A" ，如果为假，则执行 echo"not A"已执行，请参见 http://mywiki.wooledge.org/BashGuide/TestsAndConditionals
• [[]是一个bash关键字，与 [命令类似(但功能更强大).请参阅 http://mywiki.wooledge.org/BashFAQ/031 和

• I use boolean logic here. [[ $1 == A ]] is executed, and then if its true, echo "A" is executed, and if it's false, echo "not A" is executed, See http://mywiki.wooledge.org/BashGuide/TestsAndConditionals
• [[ is a bash keyword similar to (but more powerful than) the [ command. See http://mywiki.wooledge.org/BashFAQ/031 and http://mywiki.wooledge.org/BashGuide/TestsAndConditionals Unless you're writing for POSIX sh, I recommend [[.

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