bash 将命令的输出分配给变量
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Assigning the output of a command to a variable
提问by user3114665
I am new with unix and I am writing a shell script.
我是 unix 新手，正在编写一个 shell 脚本。
When I run this line on the command prompt, it prints the total count of the number of processes which matches:
当我在命令提示符下运行这一行时，它会打印匹配的进程数的总数：
ps -ef | awk '/siebsvc –s siebsrvr/ && !/awk/ { a++ } END { print a }'
example, the output of the above line is 2 in the command prompt.
例如，上面一行在命令提示符下的输出是 2。
I want to write a shell script in which the output of the above line (2) is assigned to a variable, which will be later be used for comparison in an if statement.
我想编写一个 shell 脚本，其中将上述第 (2) 行的输出分配给一个变量，该变量稍后将用于在 if 语句中进行比较。
I am looking for something like
我正在寻找类似的东西
output= `ps -ef | awk '/siebsvc –s siebsrvr/ && !/awk/ { a++ } END { print a }'`
echo $output
But when i run it, it says output could not be found whereas I am expecting 2. Please help.
但是当我运行它时，它说找不到输出，而我期待 2。请帮忙。
回答by Marutha
You can use a $sign like:
您可以使用以下$标志：
OUTPUT=$(expression)
回答by Jed Daniels
Try:
尝试：
output=$(ps -ef | awk '/siebsvc –s siebsrvr/ && !/awk/ { a++ } END { print a }'); echo $output
Wrapping your command in $( )tells the shell to run that command, instead of attempting to set the command itself to the variable named "output". (Note that you could also use backticks `command`.)
包装您的命令会$( )告诉 shell 运行该命令，而不是尝试将命令本身设置为名为“output”的变量。（请注意，您也可以使用反引号 `command`。）
I can highly recommend http://tldp.org/LDP/abs/html/commandsub.htmlto learn more about command substitution.
我强烈推荐http://tldp.org/LDP/abs/html/commandsub.html以了解有关命令替换的更多信息。
Also, as 1_CR correctly points out in a comment, the extra space between the equals sign and the assignment is causing it to fail. Here is a simple example on my machine of the behavior you are experiencing:
此外，正如 1_CR 在评论中正确指出的那样，等号和赋值之间的额外空格导致它失败。这是我的机器上您遇到的行为的一个简单示例：
jed@MBP:~$ foo=$(ps -ef |head -1);echo $foo
UID PID PPID C STIME TTY TIME CMD
jed@MBP:~$ foo= $(ps -ef |head -1);echo $foo
-bash: UID: command not found
UID PID PPID C STIME TTY TIME CMD
回答by Jahid
If you want to do it with multiline/multiple command/s then you can do this:
如果你想用 multiline/multiple command/s 来做，那么你可以这样做：
output=$( bash <<EOF
#multiline/multiple command/s
EOF
)
Or:
或者：
output=$(
#multiline/multiple command/s
)
Example:
例子：
#!/bin/bash
output="$( bash <<EOF
echo first
echo second
echo third
EOF
)"
echo "$output"
Output:
输出：
first
second
third
