如何等待进程的某些输出然后在 Bash 中继续？
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How can I wait for certain output from a process then continue in Bash?
提问by Brad
I'm trying to write a bash script to do some stuff, start a process, wait for that process to say it's ready, and then do more stuff while that process continues to run. The issue I'm running into is finding a way to wait for that process to be ready before continuing, and allowing it to continue to run.
我正在尝试编写一个 bash 脚本来做一些事情，启动一个进程，等待该进程说它准备好了，然后在该进程继续运行时做更多的事情。我遇到的问题是找到一种方法在继续之前等待该进程准备就绪，并允许它继续运行。
In my specific case I'm trying to setup a PPP connection. I need to wait until it has connected before I run the next command. I would also like to stop the script if PPP fails to connect. pppd prints to stdout.
在我的特定情况下，我正在尝试设置 PPP 连接。我需要等到它连接后才能运行下一个命令。如果 PPP 连接失败，我还想停止脚本。pppd 打印到标准输出。
In psuedo code what I want to do is:
在伪代码中，我想做的是：
[some stuff]
echo START
[set up the ppp connection]
pppd <options> /dev/ttyUSB0
while 1
if output of pppd contains "Script /etc/ppp/ipv6-up finished (pid ####), status = 0x0"
break
if output of pppd contains "Sending requests timed out"
exit 1
[more stuff, and pppd continues to run]
echo CONTINUING
Any ideas on how to do this?
关于如何做到这一点的任何想法？
回答by Ivin
I had to do something similar waiting for a line in /var/log/syslog to appear. This is what worked for me:
我不得不做类似的事情，等待 /var/log/syslog 中的一行出现。这对我有用：
FILE_TO_WATCH=/var/log/syslog
SEARCH_PATTERN='file system mounted'
tail -f -n0 ${FILE_TO_WATCH} | grep -qe ${SEARCH_PATTERN}
if [ $? == 1 ]; then
echo "Search terminated without finding the pattern"
fi
It pipes all new lines appended to the watched file to grep and instructs grep to exit quietly as soon as the pattern is discovered. The following if statement detects if the 'wait' terminated without finding the pattern.
它将所有附加到监视文件的新行通过管道传递给 grep，并在发现模式后立即指示 grep 安静地退出。下面的 if 语句检测“等待”是否在没有找到模式的情况下终止。
回答by sblom
There's a tool called "Expect" that does almost exactly what you want. More info: http://en.wikipedia.org/wiki/Expect
有一个名为“Expect”的工具几乎可以满足您的需求。更多信息：http: //en.wikipedia.org/wiki/Expect
You might also take a look at the man pages for "chat", which is a pppd feature that does some of the stuff that expect can do.
您还可以查看“chat”的手册页，这是一个 pppd 功能，可以完成一些预期可以做的事情。
回答by Brad
The quickest solution I came up with was to run pppd with nohup in the background and check the nobup.out file for stdout. It ended up something like this:
我想出的最快的解决方案是在后台运行带有 nohup 的 pppd 并检查 nobup.out 文件中的 stdout。结果是这样的：
sudo nohup pppd [options] 2> /dev/null &
# check to see if it started correctly
PPP_RESULT="unknown"
while true; do
if [[ $PPP_RESULT != "unknown" ]]; then
break
fi
sleep 1
# read in the file containing the std out of the pppd command
# and look for the lines that tell us what happened
while read line; do
if [[ $line == Script\ /etc/ppp/ipv6-up\ finished* ]]; then
echo "pppd has been successfully started"
PPP_RESULT="success"
break
elif [[ $line == LCP:\ timeout\ sending\ Config-Requests ]]; then
echo "pppd was unable to connect"
PPP_RESULT="failed"
break
elif [[ $line == *is\ locked\ by\ pid* ]]; then
echo "pppd is already running and has locked the serial port."
PPP_RESULT="running"
break;
fi
done < <( sudo cat ./nohup.out )
done
回答by dimba
回答by Swapnil jaiswal
Sorry for the late response but a simpler way would to use wait. waitis a BASH built-in command which waits for a process to finish
抱歉回复晚了，但更简单的方法是使用等待。 wait是一个 BASH 内置命令，它等待一个进程完成
Following is the excerpt from the MAN page.
以下是 MAN 页面的摘录。
wait [n ...]
Wait for each specified process and return its termination sta-
tus. Each n may be a process ID or a job specification; if a
job spec is given, all processes in that job's pipeline are
waited for. If n is not given, all currently active child pro-
cesses are waited for, and the return status is zero. If n
specifies a non-existent process or job, the return status is
127. Otherwise, the return status is the exit status of the
last process or job waited for.
For further reference on usage: Refer to wiki page
有关用法的进一步参考： 请参阅维基页面
