Bash字符串(命令输出)相等性测试 [英] Bash string (command output) equality test

问题描述

我有一个简单的脚本来检查网页是否包含指定的字符串.看起来像:

I have a simple script to check whether webpage contains a specified string. It looks like:

#!/bin/bash
res=`curl -s "http://www.google.com" | grep "foo bar foo bar" | wc -l`
if [[ $res == "0" ]]; then
    echo "OK"
else
    echo "Wrong"
fi

如您所见，我希望获得确定"，但得到错误".

As you can see, I am looking to get "OK", but got a "Wrong".

怎么了?

如果我使用if [$ res =="0"]，它可以工作.如果我只使用res ="0"而不是res = curl...，它也可以获得所需的结果.

If I use if [ $res == "0" ], it works. If I just use res="0" instead of res=curl..., it also can obtain the desired results.

为什么会有这些差异?

推荐答案

我在 glenn jackman 中找到了答案的帮助.

I found the answer in glenn jackman's help.

在这个问题上我得到以下几点:

I get the following points in this question:

• wc -l的输出包含空格.
• 使用echo "$var"而不是echo $var
进行调试
• [[保留var中所有字符的文字值.
• [在执行之前将var扩展为其值，这是因为[实际上是test cmd，因此它遵循

• wc -l 's output contains whitespaces.
• Debugging with echo "$var" instead of echo $var
• [[ preserves the literal value of all characters within the var.
• [ expands var to their values before perform, it's because [ is actually the test cmd, so it follows Shell Expansions rules.

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