Bash：一行中的 If/Else 语句
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Bash: If/Else statement in one line
提问by Arthur Rimbun
I am trying to check if a process (assume it is called some_process) is running on a server. If it is, then echo 1, otherwise echo 0.
我试图检查一个进程（假设它被调用some_process）是否正在服务器上运行。如果是，则回显 1，否则回显 0。
This is the command that I am using but it only works partially (more info below). Note that I need to write the script in one line.
这是我正在使用的命令，但它只能部分工作（更多信息如下）。请注意，我需要在一行中编写脚本。
ps aux | grep some_proces[s] > /tmp/test.txt && if [ $? -eq 0 ]; then echo 1; else echo 0; fi
Note:The [s]in some_proces[s]is to prevent grepfrom returning itself.
注：本[s]中some_proces[s]是防止grep从返回本身。
If some_processis running, then "1"gets echoed, which is fine. However, if some_processis not running, nothing gets echoed.
如果some_process正在运行，则"1"得到回显，这很好。但是，如果some_process没有运行，则没有任何回显。
回答by William Pursell
There is no need to explicitly check $?. Just do:
无需明确检查$?。做就是了：
ps aux | grep some_proces[s] > /tmp/test.txt && echo 1 || echo 0
Note that this relies on echo not failing, which is certainly not guaranteed. A more reliable way to write this is:
请注意，这依赖于 echo 不会失败，这当然不能保证。更可靠的写法是：
if ps aux | grep some_proces[s] > /tmp/test.txt; then echo 1; else echo 0; fi
回答by ruakh
&&means "and if successful"; by placing your ifstatement on the right-hand side of it, you ensure that it will only run if grepreturns 0. To fix it, use ;instead:
&&意思是“如果成功”；通过将您的if语句放在它的右侧，您可以确保它仅在grepreturn 时运行0。要修复它，请;改用：
ps aux | grep some_proces[s] > /tmp/test.txt ; if [ $? -eq 0 ]; then echo 1; else echo 0; fi
ps aux | grep some_proces[s] > /tmp/test.txt ; if [ $? -eq 0 ]; then echo 1; else echo 0; fi
(or just use a line-break).
（或只是使用换行符）。
回答by John Gilmer
Use grep -vcto ignore grepin the psoutput and count the lines simultaneously.
使用grep -vc忽视grep的ps输出，同时计数线。
if [[ $(ps aux | grep process | grep -vc grep) > 0 ]] ; then echo 1; else echo 0 ; fi
回答by Costi Ciudatu
You can make full use of the &&and ||operators like this:
您可以像这样充分利用&&and||运算符：
ps aux | grep some_proces[s] > /tmp/test.txt && echo 1 || echo 0
For excluding grep itself, you could also do something like:
为了排除 grep 本身，您还可以执行以下操作：
ps aux | grep some_proces | grep -vw grep > /tmp/test.txt && echo 1 || echo 0
