将 Bash 字符串文字与局部变量进行比较
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Compare a Bash string literal to a local variable
提问by Anderson Green
#!/bin/bash
function getComment(){
local lang=;
local theComment=;
if [$lang == "Java"] #Surprisingly, an error occurs here: prog.sh: line 6: [Java: command not found
then
echo "//"$theComment; return;
else
echo "Language not found!"; return;
fi
}
getComment "Java" "Whoo!";
exit $?
I'm writing a Bash script that compares a variable to a string literal, and I'm using [$lang == "Java"](as shown above) to compare the value of langto "Java". However, this comparison produces the following error:
我正在写一个bash脚本，一个变量进行比较，以一个字符串，以及我使用[$lang == "Java"]（如上所示）比较的值lang到"Java"。但是，这种比较会产生以下错误：
stderr:
prog.sh: line 6: [Java: command not found
I've tried using [$lang -eq "Java"]and ($lang -eq "Java")as well, but those statements didn't work either, and they produced exactly the same error.
我也尝试过使用[$lang -eq "Java"]and ($lang -eq "Java")，但是这些语句也不起作用，并且它们产生了完全相同的错误。
Why is this error occurring, and what is the correct way to compare a local variable to a string literal?
为什么会发生此错误，将局部变量与字符串文字进行比较的正确方法是什么？
回答by Barmar
You need spaces around [and ]:
你需要周围的空间[和]：
if [ "$lang" = "Java" ]
[is a command (it's a synonym for test), and like any other command you delimit the parameters with spaces.
[是一个命令（它是 的同义词test），并且像任何其他命令一样用空格分隔参数。
You should also put variables in double quotes, in case the value is empty or contains whitespace or wildcard characters.
您还应该将变量放在双引号中，以防值为空或包含空格或通配符。
Finally, the operator to perform string comparison is =, although some versions of testallow ==as an extension.
最后，执行字符串比较的运算符是=，尽管某些版本test允许==作为扩展名。
回答by Pablo Niklas
First, you have to enclose the variable between double quotes, because the variable could have some spaces or special characters.
首先，您必须用双引号将变量括起来，因为变量可能有一些空格或特殊字符。
Finally remember that "[" it's an executable by itself (usually is in /bin).
最后记住 "[" 它本身就是一个可执行文件（通常在 /bin 中）。
if [ "$lang" == "Java" ]; then
