Shell 相等运算符(=、==、-eq) [英] Shell equality operators (=, ==, -eq)

问题描述

=、== 和 -eq 在 shell 脚本中有什么区别?

What is the difference between =, == and -eq in shell scripting?

以下有区别吗?

[ $a = $b ]
[ $a == $b ]
[ $a -eq $b ]

难道只是= 和== 只在变量包含数字时使用?

Is it simply that = and == are only used when the variables contain numbers?

推荐答案

相反:= 和 == 用于字符串比较，-eq 用于数字.-eq 与 -lt、-le、-gt、-ge 属于同一家族 和 -ne，如果这有助于您记住哪个是哪个.

It's the other way around: = and == are for string comparisons, -eq is for numeric ones. -eq is in the same family as -lt, -le, -gt, -ge, and -ne, if that helps you remember which is which.

== 是一种 bash 主义.最好使用 POSIX =.在 bash 中，两者是等价的，而在普通 sh 中 = 是唯一保证可以工作的.

== is a bash-ism, by the way. It's better to use the POSIX =. In bash the two are equivalent, and in plain sh = is the only one guaranteed to work.

$ a=foo
$ [ "$a" = foo ]; echo "$?"       # POSIX sh
0
$ [ "$a" == foo ]; echo "$?"      # bash specific
0
$ [ "$a" -eq foo ]; echo "$?"     # wrong
-bash: [: foo: integer expression expected
2

(旁注:引用那些变量扩展！不要遗漏上面的双引号.)

(Side note: Quote those variable expansions! Do not leave out the double quotes above.)

如果您正在编写 #!/bin/bash 脚本，那么我推荐 使用 [[ 代替.双重形式具有更多功能、更自然的语法和更少的陷阱.$a 周围不再需要双引号，例如:

If you're writing a #!/bin/bash script then I recommend using [[ instead. The doubled form has more features, more natural syntax, and fewer gotchas that will trip you up. Double quotes are no longer required around $a, for one:

$ [[ $a == foo ]]; echo "$?"      # bash specific
0

另见:

• Bash 中的 [ 和 [[ 有什么区别?

这篇关于Shell 相等运算符(=、==、-eq)的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！