blocks|key|1222650|text|我认为这是一个糟糕的解决方案，这会导致竞争条件的出现。如果进程在您的测试和终止调用之间终止了，该怎么办？那么杀死就会失败。那么，为什么不在所有情况下都尝试kill，并检查它的返回值以了解它是如何运行的呢？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1222651|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

I think that is a bad solution, that opens up for race conditions. What if the process dies between your test and your call to kill? Then kill will fail. So why not just try the kill in all cases, and check its return value to find out how it went?

blocks|key|1222689|text|带有-p+$PID的ps命令可以执行以下操作：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1222690|$+ps+-p+3531
++PID+TTY++++++++++TIME+CMD
+3531+?++++++++00:03:07+emacs|code-block|syntax|javascript|1222691|entityMap^0|2|7|A|2|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

<code>ps</code> command with <code>-p $PID</code> can do this:

<pre><code>$ ps -p 3531
 PID TTY TIME CMD
 3531 ? 00:03:07 emacs
</code></pre>

blocks|key|1222756|text|要检查进程是否存在，请使用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1222757|kill+-0+$pid|code-block|syntax|javascript|1222758|但就像@unwind+said一样，如果您希望它在任何情况下终止，那么只需|offset|length|1222759|kill+$pid|1222760|否则，您将遇到竞争条件，在第一次kill+-0之后，进程可能已经消失。|style|CODE|1222761|如果您想忽略kill的文本输出，并根据退出代码执行一些操作，您可以|1222762|if+!+kill+$pid+>+/dev/null+2>&1;+then
++++echo+"Could+not+send+SIGTERM+to+process+$pid"+>&2
fi|1222763|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/3043991/4575793^0|0|0|3|C|0|0|0|G|7|0|6|4|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|14|8|@]|9|@$I|15|J|16|1|17]]|A|$]]|$1|K|3|L|5|D|7|18|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|19|8|@$I|1A|J|1B|O|P]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1C|8|@$I|1D|J|1E|O|P]]|9|@]|A|$]]|$1|S|3|T|5|D|7|1F|8|@]|9|@]|A|$E|F]]|$1|U|3|-4|5|6|7|1G|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]]]

To check for the existence of a process, use
<pre><code>kill -0 $pid
</code></pre>
But just as <a href="https://stackoverflow.com/a/3043991/4575793">@unwind said</a>, if you want it to terminate in any case, then just
<pre><code>kill $pid
</code></pre>
Otherwise you will have a race condition, where the process might have disappeared after the first <code>kill -0</code>.
If you want to ignore the text output of <code>kill</code> and do something based on the exit code, you can
<pre><code>if ! kill $pid &gt; /dev/null 2&gt;&amp;1; then
 echo &quot;Could not send SIGTERM to process $pid&quot; &gt;&amp;2
fi
</code></pre>

blocks|key|1008382|text|看起来你想|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1008383|wait+$PID|code-block|syntax|javascript|1008384|它将在$pid完成时返回。|offset|length|style|CODE|1008385|否则，您可以使用|1008386|ps+-p+$PID|1008387|检查进程是否仍然有效(这比kill+-0+$pid更有效，因为即使您不拥有pid，它也可以工作)。|1008388|entityMap^0|0|0|3|4|0|0|0|D|C|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@$I|X|J|Y|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|Z|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|11|8|@$I|12|J|13|K|L]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|T|$]]

It seems like you want

<pre><code>wait $PID
</code></pre>

which will return when <code>$pid</code> finishes.

Otherwise you can use

<pre><code>ps -p $PID
</code></pre>

to check if the process is still alive (this is more effective than <code>kill -0 $pid</code> because it will work even if you don't own the pid).

blocks|key|1222854|text|如果您的系统实现了procfs接口，您可以只检查是否有一个特殊的文件/proc/$PID/status|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1222855|if+[+-e+/proc/$PID/status+];+then
++++echo+"process+exists"
fi|code-block|syntax|javascript|1222856|否则，您可以使用ps程序：|1222857|if+[+-n+"$(ps+-p+$PID+-o+pid=)"+]|1222858|在后一种形式中，-o+pid=是一种输出格式，它只显示没有标题的进程ID列。对于非空字符串运算符-n，引号为necessary，以提供有效结果。|1222859|entityMap|0|LINK|mutability|MUTABLE|url|https://www.wikiwand.com/en/Procfs|1|http://tldp.org/LDP/abs/html/comparison-ops.html#STRTEST^0|Y|H|9|6|0|0|0|8|2|0|0|8|7|1C|2|1I|9|1|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@$9|13|A|14|1|15]]|E|$]]|$1|F|3|G|5|H|7|16|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|1A|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1B|8|@$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]]|D|@$9|1G|A|1H|1|1I]]|E|$]]|$1|Q|3|-4|5|6|7|1J|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]|Y|$5|T|U|V|E|$W|Z]]]]

If your system implements <a href="https://www.wikiwand.com/en/Procfs" rel="nofollow noreferrer">procfs</a> interface, you can just check if there is a special file <code>/proc/$PID/status</code>:
<pre><code>if [ -e /proc/$PID/status ]; then
 echo &quot;process exists&quot;
fi
</code></pre>
otherwise you can use <code>ps</code> program:
<pre><code>if [ -n &quot;$(ps -p $PID -o pid=)&quot; ]
</code></pre>
In the latter form, <code>-o pid=</code> is an output format to display only the process ID column with no header. The quotes are <a href="http://tldp.org/LDP/abs/html/comparison-ops.html#STRTEST" rel="nofollow noreferrer">necessary</a> for non-empty string operator <code>-n</code> to give valid result.

blocks|key|1222914|text|例如，在GNU/Linux中，您可以使用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1222915|Pid=$(pidof+`process_name`)

if+[+$Pid+>+0+];+then

+++do+something
else

+++do+something
fi+|code-block|syntax|javascript|1222916|或者类似于|1222917|Pin=$(ps+-A+%7C+grep+name+%7C+awk+'print+$4}')
echo+$PIN|1222918|这会显示应用程序的名称，只显示没有ID的名称。|1222919|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

For example in GNU/Linux you can use:

<pre><code>Pid=$(pidof `process_name`)

if [ $Pid &gt; 0 ]; then

 do something
else

 do something
fi 
</code></pre>

Or something like

<pre><code>Pin=$(ps -A | grep name | awk 'print $4}')
echo $PIN
</code></pre>

and that shows you the name of the app, just the name without ID.

In a bash script, I want to do the following (in pseudo-code):

<pre><code>if [ a process exists with $PID ]; then

 kill $PID 

fi
</code></pre>

What's the appropriate expression for the conditional statement?

How to check if a process id (PID) exists

Linux

在bash脚本中，我想(用伪代码)执行以下操作：if [ a process exists with $PID ]; then    kill $PID fi条件语句的适当表达式是什么？

问如何检查进程id (PID)是否存在
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