bash shell脚本中的wait命令
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wait command in shell script
提问by Sam
fork(){
i=0
count=0
while (($count<5))
do
fpfunction &
pid=$!
#Ensure the pid is available
if [ -z "$pid" ]; then
echo "IS NULL"
else
Array[$i]=$pid
echo "PID is $pid"
fi
wait [$pid]
i=$((i+1))
count=$(( count+1 ))
done
echo "PID: ${Array[*]}"
}
The fpfunction() only echo a string, so I dont write it here.
fpfunction() 只回显一个字符串，所以我不写在这里。
My understanding to wait() is it will wait a child process to complete and then return a value.
我对 wait() 的理解是它会等待子进程完成然后返回一个值。
I put wait() in my script because I want to ensure all child processes are finished.
我将 wait() 放在我的脚本中，因为我想确保所有子进程都已完成。
However, the error occured
然而，错误发生了
not a pid or valid job spec
不是 pid 或有效的工作规范
Is my understanding wrong? please let me know how to fix this issue.
我的理解有误吗？请让我知道如何解决这个问题。
Thanks a lot.
非常感谢。
回答by paxdiablo
If the process ID is, for example, 42 then your waitinstruction becomes:
例如，如果进程 ID 是 42，那么您的wait指令将变为：
wait [42]
which is not what you want - the square brackets are a problem. It should be:
这不是您想要的 - 方括号是一个问题。它应该是：
wait $pid
as per the following transcript:
根据以下成绩单：
pax> date ; sleep 60 &
Wednesday 17 July 10:43:51 WST 2013
[1] 5200
pax> pid=$! ; echo $pid
5200
pax> wait [$pid]
bash: wait: '[5200]': not a pid or valid job spec
pax> wait $pid ; date
[1]+ Done sleep 60
Wednesday 17 July 10:44:51 WST 2013
And, just as an aside (irrelevant to the answer), wait()is better suited to the C wait()function.If you're using waitfrom the shell,you would normally leave off the parentheses.
而且，顺便说一句（与答案无关），wait()更适合 Cwait()函数。如果您wait从shell使用，通常会省略括号。
