如何等待进程的某些输出然后继续Bash？

Question

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就绪,然后在该进程继续运行时再做更多的事情.我遇到的问题是找到一种方法,在继续之前等待该过程准备就绪,并允许它继续运行.

在我的具体情况下,我正在尝试建立PPP连接.在运行下一个命令之前,我需要等到它已连接.如果PPP无法连接,我还想停止脚本.pppd打印到stdout.

在psuedo代码中我想要做的是:

[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

关于如何做到这一点的任何想法？

Answer 1

我必须做类似的事情,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

它会将附加到监视文件的所有新行管道为grep,并指示grep在发现模式后立即安静地退出.以下if语句检测"wait"是否在没有找到模式的情况下终止.

Answer 2

我想出的最快解决方案是在后台使用 nohup 运行 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

Answer 3

有一个名为“Expect”的工具几乎可以完全满足您的需求。更多信息： http: //en.wikipedia.org/wiki/Expect

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完成的操作。