I'm trying to get an if statement to work in Bash (using Ubuntu):
我试图在Bash中获得一个if语句(使用Ubuntu):
#!/bin/bash
s1="hi"
s2="hi"
if ["$s1" == "$s2"]
then
echo match
fi
I've tried various forms of the if statement, using [["$s1" == "$s2"]], with and without quotes, using =, == and -eq, but I still get the following error:
我尝试了各种形式的if语句，使用[[$s1] == "$s2"]，使用=、==和-eq，但我仍然得到以下错误:
[hi: command not found
[你好:命令没有找到
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 $s1 contains $s2, so how can I do that?
最后，我想说，如果$s1包含$s2，我该怎么做呢?
I did just work out the spaces bit.. :/ How do I say contains?
我刚才算出了空格。/我怎么说包含?
I tried
我试着
if [[ "$s1" == "*$s2*" ]]
but it didn't work.
但它不工作。
11 个解决方案
#1
520
For string comparison, use:
对于字符串比较,使用:
if [ "$s1" == "$s2" ]
For the a contains b, use:
a含b，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:
缺点:
if ["$s1" == "$s2"]
good:
好:
if [ "$s1" == "$s2" ]
#2
131
You need spaces:
你需要空间:
if [ "$s1" == "$s2" ]
#3
106
You should be careful to leave a space between the sign of '[' and double quotes where the variable contains this:
您应该注意在“[”和“双引号”的符号之间留出空格。
if [ "$s1" == "$s2" ]; then
# ^ ^ ^ ^
echo match
fi
The ^s show the blank spaces you need to leave.
你需要离开的空白区域。
#4
26
I suggest this one:
我建议这个:
if [ "$a" = "$b" ]
Notice the white space between the openning/closing brackets and the variables and also the white spaces wrapping the '=' sign.
注意openning/关闭括号和变量之间的空白，以及包装“=”符号的空格。
Also, be careful of your script header. It's not the same thing whether you use
同时，要注意你的脚本标题。这和你用的不一样。
#!/bin/bash
or
或
#!/bin/sh
这是源。
#5
10
I would suggest:
我建议:
#!/bin/bash
s1="hi"
s2="hi"
if [ $s1 = $s2 ]
then
echo match
fi
Without the double quotes and with only one equals.
没有双引号，只有一个等于。
#6
8
This question has already great answers but here it appears that there is a slight confusion between using single equal and double equals in
这个问题已经有了很好的答案，但是在这里，使用单值和双等号的问题似乎有点混淆。
if [ "$s1" == "$s2" ]
The main difference lies in which scripting language are you using. If you are using bash then include #!/bin/bash in the starting of the script and save your script as filename.bash. To execute use bash filename.bash - then you have to use ==.
主要的区别在于您使用的脚本语言。如果您正在使用bash，那么请包括#!/bin/bash在脚本的开头，将脚本保存为filename.bash。要执行使用bash文件名。bash—然后您必须使用==。
If you are using sh then use #!/bin/sh and save your script as filename.sh. To execute use sh filename.sh - then you have to use single =. Avoid intermixing them.
如果您正在使用sh，那么请使用#!/bin/sh并将脚本保存为filename.sh。执行使用sh文件名。sh -然后你必须使用single =。避免混合它们。
#7
7
$ if [ "$s1" == "$s2" ]; then echo match; fi
match
$ test "s1" = "s2" ;echo match
match
$
#8
6
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.
我现在没有访问linux的权限，但实际上是一个程序(和一个bash构建程序)，所以我认为您必须在(和第一个参数)之间放置一个空格。
Also note that string equality operator seems to be a single =
还要注意，字符串相等运算符似乎是一个单独的=。
#9
3
This is more clarification than answer ! Yes , the clue is in the error message:
这比回答更清楚!是的，线索在错误信息中:
[hi: command not found
[你好:命令没有找到
which shows you that your "hi" has been concatenated to the "[".
这表明你的“hi”已经连接到“[”。
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) "$s1" which are immediately next to each other in your question, are joined (as is correct for Bash) and it then tries to find a command in that position: [hi - which is unknown to Bash.
与传统的编程语言不同，在Bash中，“(”是一个命令，就像更明显的“ls”等)——它不是专门处理的，只是因为它是一个符号，因此“(”和“替换”)“$s1”在您的问题中是相邻的，是连接的(对于Bash来说是正确的)，然后它试图在这个位置找到一个命令:[hi -，这是Bash所不知道的。
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语言和其他一些语言中，“[”将被看作是一个不同的“字符类”，并且会从下面的“hi”中分离出来。
Hence you require a space after the opening "[".
因此，在打开后需要一个空格。
#10
2
#!/bin/bash
s1="hi"
s2="hi"
if [ "x$s1" == "x$s2" ]
then
echo match
fi
Adding additional string inside makes it more safe.
在内部添加额外的字符串会使其更加安全。
You could also use other notation for single line commands:
你也可以用其他的符号来表示单行命令:
[ "x$s1" == "x$s2" ] && echo match
#11
2
For a version with pure Bash and without test, but really ugly, try:
对于一个纯Bash和没有测试的版本，但是非常丑陋，尝试:
if ( exit "${s1/*$s2*/0}" )2>/dev/null
then
echo match
fi
Explanation: In ( )an extra subshell is opened. It exits with 0 if there was a match, and it tries to exit with $s1 if there was no match which raises an error (ugly). This error is directed to /dev/null.
说明:在()一个额外的子壳被打开。如果有匹配，它会以0退出，如果没有匹配，则试图以$s1退出，这将导致错误(丑陋)。这个错误指向/dev/null。
#1
520
For string comparison, use:
对于字符串比较,使用:
if [ "$s1" == "$s2" ]
For the a contains b, use:
a含b，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:
缺点:
if ["$s1" == "$s2"]
good:
好:
if [ "$s1" == "$s2" ]
#2
131
You need spaces:
你需要空间:
if [ "$s1" == "$s2" ]
#3
106
You should be careful to leave a space between the sign of '[' and double quotes where the variable contains this:
您应该注意在“[”和“双引号”的符号之间留出空格。
if [ "$s1" == "$s2" ]; then
# ^ ^ ^ ^
echo match
fi
The ^s show the blank spaces you need to leave.
你需要离开的空白区域。
#4
26
I suggest this one:
我建议这个:
if [ "$a" = "$b" ]
Notice the white space between the openning/closing brackets and the variables and also the white spaces wrapping the '=' sign.
注意openning/关闭括号和变量之间的空白，以及包装“=”符号的空格。
Also, be careful of your script header. It's not the same thing whether you use
同时，要注意你的脚本标题。这和你用的不一样。
#!/bin/bash
or
或
#!/bin/sh
这是源。
#5
10
I would suggest:
我建议:
#!/bin/bash
s1="hi"
s2="hi"
if [ $s1 = $s2 ]
then
echo match
fi
Without the double quotes and with only one equals.
没有双引号，只有一个等于。
#6
8
This question has already great answers but here it appears that there is a slight confusion between using single equal and double equals in
这个问题已经有了很好的答案，但是在这里，使用单值和双等号的问题似乎有点混淆。
if [ "$s1" == "$s2" ]
The main difference lies in which scripting language are you using. If you are using bash then include #!/bin/bash in the starting of the script and save your script as filename.bash. To execute use bash filename.bash - then you have to use ==.
主要的区别在于您使用的脚本语言。如果您正在使用bash，那么请包括#!/bin/bash在脚本的开头，将脚本保存为filename.bash。要执行使用bash文件名。bash—然后您必须使用==。
If you are using sh then use #!/bin/sh and save your script as filename.sh. To execute use sh filename.sh - then you have to use single =. Avoid intermixing them.
如果您正在使用sh，那么请使用#!/bin/sh并将脚本保存为filename.sh。执行使用sh文件名。sh -然后你必须使用single =。避免混合它们。
#7
7
$ if [ "$s1" == "$s2" ]; then echo match; fi
match
$ test "s1" = "s2" ;echo match
match
$
#8
6
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.
我现在没有访问linux的权限，但实际上是一个程序(和一个bash构建程序)，所以我认为您必须在(和第一个参数)之间放置一个空格。
Also note that string equality operator seems to be a single =
还要注意，字符串相等运算符似乎是一个单独的=。
#9
3
This is more clarification than answer ! Yes , the clue is in the error message:
这比回答更清楚!是的，线索在错误信息中:
[hi: command not found
[你好:命令没有找到
which shows you that your "hi" has been concatenated to the "[".
这表明你的“hi”已经连接到“[”。
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) "$s1" which are immediately next to each other in your question, are joined (as is correct for Bash) and it then tries to find a command in that position: [hi - which is unknown to Bash.
与传统的编程语言不同，在Bash中，“(”是一个命令，就像更明显的“ls”等)——它不是专门处理的，只是因为它是一个符号，因此“(”和“替换”)“$s1”在您的问题中是相邻的，是连接的(对于Bash来说是正确的)，然后它试图在这个位置找到一个命令:[hi -，这是Bash所不知道的。
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语言和其他一些语言中，“[”将被看作是一个不同的“字符类”，并且会从下面的“hi”中分离出来。
Hence you require a space after the opening "[".
因此，在打开后需要一个空格。
#10
2
#!/bin/bash
s1="hi"
s2="hi"
if [ "x$s1" == "x$s2" ]
then
echo match
fi
Adding additional string inside makes it more safe.
在内部添加额外的字符串会使其更加安全。
You could also use other notation for single line commands:
你也可以用其他的符号来表示单行命令:
[ "x$s1" == "x$s2" ] && echo match
#11
2
For a version with pure Bash and without test, but really ugly, try:
对于一个纯Bash和没有测试的版本，但是非常丑陋，尝试:
if ( exit "${s1/*$s2*/0}" )2>/dev/null
then
echo match
fi
Explanation: In ( )an extra subshell is opened. It exits with 0 if there was a match, and it tries to exit with $s1 if there was no match which raises an error (ugly). This error is directed to /dev/null.
说明:在()一个额外的子壳被打开。如果有匹配，它会以0退出，如果没有匹配，则试图以$s1退出，这将导致错误(丑陋)。这个错误指向/dev/null。