bash 用于比较的 Shell 脚本算术运算符
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Shell Scripting Arithmetic Operators for Comparison
提问by Sugihara
I am trying to learn shell scripting and following the tutorials on tutorialspoint when I came across this problem with arithmetic comparison.
当我在算术比较中遇到这个问题时，我正在尝试学习 shell 脚本并遵循 tutorialspoint 上的教程。
$VAL1=10
$VAL2=20
$VAL3=10
if [ $VAL1 == $VAL2 ]
then
echo "equal"
else
echo "not equal"
fi
but I got a [: ==: unexpected operatorI am not sure why the comparison operator did not work. I know I can also use rational operators, but I want to know why '==' is not defined.
但我得到了一个[: ==: unexpected operator我不知道为什么比较运算符不起作用。我知道我也可以使用有理运算符，但我想知道为什么没有定义“==”。
回答by sampson-chen
You want to change it to:
您想将其更改为：
VAL1=10
VAL2=20
VAL3=10
if [ "$VAL1" -eq "$VAL2" ]
then
echo "equal"
else
echo "not equal"
fi
Explanations:
说明：
- Don't add the
$for the lvalue (variable being assigned) in an assignment. - Always wrap your variables with double-quotes in tests. The
[: ==: unexpected operatorerror you got is because, sinceVAL1/VAL2were not assigned properly earlier, ksh expansion of your test actually ends up resolving to this:if [ == ]- (but you see that it's actually not a problem about==being undefined) - Use the following for numeric comparisons instead of the
==notation:-eq(==)-ne(!=)-gt(>)-ge(>=)-lt(<)-le(<=)
- 不要
$在赋值中为左值（被赋值的变量）添加。 - 在测试中始终用双引号将变量括起来。
[: ==: unexpected operator你得到的错误是因为VAL1/VAL2之前没有正确分配，你的测试的 ksh 扩展实际上最终解决了这个if [ == ]问题==：-（但你看到它实际上不是未定义的问题） - 使用以下进行数字比较而不是
==表示法：-eq(==)-ne(!=)-gt(>)-ge(>=)-lt(<)-le(<=)
