如何将 Bash 命令的输出分配给变量？
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原文地址: http://stackoverflow.com/questions/2314750/
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How to assign the output of a Bash command to a variable?
提问by Zenet
I have a problem putting the content of pwdcommand into a shell variable that I'll use later.
我在将pwd命令的内容放入稍后将使用的 shell 变量时遇到问题。
Here is my shell code (the loop doesn't stop):
这是我的 shell 代码（循环不会停止）：
#!/bin/bash
pwd= `pwd`
until [ $pwd = "/" ]
do
echo $pwd
ls && cd .. && ls
$pwd= `pwd`
done
Could you spot my mistake, please?
你能发现我的错误吗？
回答by John Weldon
Try:
尝试：
pwd=`pwd`
or
或者
pwd=$(pwd)
Notice no spaces after the equals sign.
注意等号后没有空格。
Also as Mr. Weiss points out; you don't assign to $pwd, you assign to pwd.
同样正如魏斯先生指出的那样；你不分配给$pwd，你分配给pwd。
回答by Johannes Weiss
In shell you assign to a variable without the dollar-sign:
在 shell 中，您分配给一个没有美元符号的变量：
TEST=`pwd`
echo $TEST
that's better (and can be nested) but is not as portable as the backtics:
这更好（并且可以嵌套）但不如 backtics 便携：
TEST=$(pwd)
echo $TEST
Always remember: the dollar-sign is only used when reading a variable.
永远记住：美元符号仅在读取变量时使用。
回答by Gilles 'SO- stop being evil'
In this specific case, note that bash has a variable called PWDthat contains the current directory: $PWDis equivalent to `pwd`. (So do other shells, this is a standard feature.) So you can write your script like this:
在这种特定情况下，请注意 bash 有一个名为的变量PWD，其中包含当前目录：$PWD相当于`pwd`. （其他 shell 也是如此，这是一个标准特性。）所以你可以像这样编写你的脚本：
#!/bin/bash
until [ "$PWD" = "/" ]; do
echo "$PWD"
ls && cd .. && ls
done
Note the use of double quotes around the variable references. They are necessary if the variable (here, the current directory) contains whitespace or wildcards (\[?*), because the shell splits the result of variable expansions into words and performs globbing on these words. Always double-quote variable expansions "$foo"and command substitutions "$(foo)"(unless you specifically know you have not to).
请注意在变量引用周围使用双引号。如果变量（此处为当前目录）包含空格或通配符 ( \[?*)，则它们是必需的，因为 shell 将变量扩展的结果拆分为单词并对这些单词执行通配符。始终双引号变量扩展"$foo"和命令替换"$(foo)"（除非您明确知道您不必这样做）。
In the general case, as other answers have mentioned already:
在一般情况下，正如其他答案已经提到的：
- You can't use whitespace around the equal sign in an assignment:
var=value, notvar = value - The
$means “take the value of this variable”, so you don't use it when assigning:var=value, not$var=value
- 您不能在赋值中的等号周围使用空格：
var=value, notvar = value - 的
$意思是“利用这个变量的值”，所以分配当你不使用它：var=value不是$var=value
回答by Jim
You can also do way more complex commands, just to round out the examples above. So, say I want to get the number of processes running on the system and store it in the ${NUM_PROCS}variable.
您还可以执行更复杂的命令，只是为了完善上面的示例。因此，假设我想获取系统上运行的进程数并将其存储在${NUM_PROCS}变量中。
All you have to so is generate the command pipeline and stuff it's output (the process count) into the variable.
您所要做的就是生成命令管道并将其输出（进程计数）填充到变量中。
It looks something like this:
它看起来像这样：
NUM_PROCS=$(ps -e | sed 1d | wc -l)
I hope that helps add some handy information to this discussion.
我希望这有助于为这次讨论添加一些方便的信息。
回答by Nikolas Wolfe
Here's your script...
这是你的脚本...
DIR=$(pwd)
echo $DIR
while [ "$DIR" != "/" ]; do
cd ..
DIR=$(pwd)
echo $DIR
done
Note the spaces, use of quotes, and $ signs.
注意空格、引号的使用和 $ 符号。
