如何在 Bash 的“if”语句中比较两个字符串变量？

How do I compare two string variables in an 'if' statement in Bash?

提问by Mr Shoubs

I'm trying to get an ifstatement to work in Bash(using Ubuntu):

我正在尝试获得if在Bash 中工作的声明（使用Ubuntu）：

#!/bin/bash

s1="hi"
s2="hi"

if ["$s1" == "$s2"]
then
  echo match
fi

I've tried various forms of the ifstatement, using [["$s1" == "$s2"]], with and without quotes, using =, ==and -eq, but I still get the following error:

我已经试过各种形式的if陈述，使用[["$s1" == "$s2"]]，不管有没有行情，使用=，==和-eq，但我仍然得到以下错误：

[hi: command not found

[嗨：找不到命令

I've looked at various sites and tutorials and copied those, but it doesn't work - what am I doing wrong?

我查看了各种网站和教程并复制了它们，但它不起作用 - 我做错了什么？

Eventually, I want to say if $s1contains $s2, so how can I do that?

最后，我想说 if $s1contains $s2，那我该怎么做呢？

I did just work out the spaces bit... :/ How do I say contains?

我只是算出空格位...：/我怎么说contains？

I tried

我试过

if [[ "$s1" == "*$s2*" ]]

but it didn't work.

但它没有用。

回答by moinudin

For string comparison, use:

对于字符串比较，请使用：

if [ "$s1" == "$s2" ]

For the acontains b, use:

对于acontains b，请使用：

if [[ $s1 == *"$s2"* ]]

(and make sure to add spaces between the symbols):

（并确保在符号之间添加空格）：

Bad:

坏的：

if ["$s1" == "$s2"]

Good:

好的：

if [ "$s1" == "$s2" ]

回答by unwind

You need spaces:

你需要空格：

if [ "$s1" == "$s2" ]

回答by trejo08

You should be careful to leave a space between the sign of '[' and double quotes where the variable contains this:

您应该小心在 '[' 的符号和包含以下变量的双引号之间留一个空格：

if [ "$s1" == "$s2" ]; then
#   ^     ^  ^     ^
   echo match
fi

The ^s show the blank spaces you need to leave.

在^S显示你需要离开的空白。

回答by Abderrazak BOUADMA

I suggest this one:

我推荐这个：

if [ "$a" = "$b" ]

Notice the white space between the openning/closing brackets and the variables and also the white spaces wrapping the '=' sign.

请注意开始/结束括号和变量之间的空白以及包裹“=”符号的空白。

Also, be careful of your script header. It's not the same thing whether you use

另外，请注意您的脚本标题。你用不一样

#!/bin/bash

or

或者

#!/bin/sh

Here's the source.

这是来源。

回答by Mike Q

Bash 4+ examples. Note: not using quotes will cause issues when words contain spaces, etc. Always quote in Bash IMO.

Bash 4+ 示例。注意：当单词包含空格等时，不使用引号会导致问题。在 Bash IMO 中始终引用。

Here are some examples Bash 4+:

以下是 Bash 4+ 的一些示例：

Example 1, check for 'yes' in string (case insensitive):

示例 1，检查字符串中的 'yes'（不区分大小写）：

if [[ "${str,,}" == *"yes"* ]] ;then

Example 2, check for 'yes' in string (case insensitive):

示例 2，检查字符串中的 'yes'（不区分大小写）：

if [[ "$(echo "$str" | tr '[:upper:]' '[:lower:]')" == *"yes"* ]] ;then

Example 3, check for 'yes' in string (case sensitive):

示例 3，检查字符串中的 'yes'（区分大小写）：

 if [[ "${str}" == *"yes"* ]] ;then

Example 4, check for 'yes' in string (case sensitive):

示例 4，检查字符串中的 'yes'（区分大小写）：

 if [[ "${str}" =~ "yes" ]] ;then

Example 5, exact match (case sensitive):

示例 5，完全匹配（区分大小写）：

 if [[ "${str}" == "yes" ]] ;then

Example 6, exact match (case insensitive):

示例 6，完全匹配（不区分大小写）：

 if [[ "${str,,}" == "yes" ]] ;then

Example 7, exact match:

例7，完全匹配：

 if [ "$a" = "$b" ] ;then

回答by jzrk

I would suggest:

我会建议：

#!/bin/bash

s1="hi"
s2="hi"

if [ $s1 = $s2 ]
then
  echo match
fi

Without the double quotes and with only one equals.

没有双引号，只有一个equals。

回答by does_it_matter

This question has already great answers, but here it appears that there is a slight confusion between using single equal and double equals in

这个问题已经有了很好的答案，但在这里似乎在使用单等号和双等号之间存在轻微的混淆

if [ "$s1" == "$s2" ]

The main difference lies in which scripting language you are using. If you are using Bash then include #!/bin/bashin the starting of the script and save your script as filename.bash. To execute, use bash filename.bash- then you have to use ==.

主要区别在于您使用的脚本语言。如果您使用的是 Bash，则#!/bin/bash在脚本的开头包含并保存您的脚本为filename.bash. 要执行，请使用bash filename.bash- 然后您必须使用==.

If you are using shthen use #!/bin/shand save your script as filename.sh. To execute use sh filename.sh- then you have to use single =. Avoid intermixing them.

如果您使用的是sh，则使用#!/bin/sh脚本并将其另存为filename.sh. 要执行 use sh filename.sh- 那么你必须使用 single =。避免混合它们。

回答by qwerty

$ if [ "$s1" == "$s2" ]; then echo match; fi
match
$ test "s1" = "s2" ;echo match
match
$

回答by Mrki

I don't have access to a Linux box right now, but [is actually a program (and a Bash builtin), so I think you have to put a space between [and the first parameter.

我现在无法访问 Linux 机器，但[实际上是一个程序（和内置的 Bash），所以我认为你必须[在第一个参数和第一个参数之间放置一个空格。

Also note that the string equality operator seems to be a single =.

另请注意，字符串相等运算符似乎是单个=.

回答by MikeW

This is more a clarification than an answer! Yes, the clue is in the error message:

这与其说是回答，不如说是澄清！是的，线索在错误消息中：

[hi: command not found

[嗨：找不到命令

which shows you that your "hi" has been concatenated to the "[".

这表明您的“hi”已连接到“[”。

Unlike in more traditional programming languages, in Bash, "[" is a command just like the more obvious "ls", etc. - it's not treated specially just because it's a symbol, hence the "[" and the (substituted) "$s1" which are immediately next to each other in your question, are joined (as is correct for Bash), and it then tries to find a command in that position: [hi - which is unknown to Bash.

与更传统的编程语言不同，在 Bash 中，“[”是一个命令，就像更明显的“ls”等一样 - 它不会因为它是一个符号而被特殊对待，因此“[”和（替代的）“$ s1" 在您的问题中紧挨着对方，加入（对于 Bash 是正确的），然后它会尝试在该位置找到一个命令：[hi - Bash 不知道。

In C and some other languages, the "[" would be seen as a different "character class" and would be disjoint from the following "hi".

在 C 和其他一些语言中，“[”将被视为不同的“字符类”，并且与后面的“hi”不相交。

Hence you require a space after the opening "[".

因此，您需要在开头“[”之后留一个空格。