Bash while true loop with dynamic execution criteria (variable)

Good day to all, thanks to all supporting stackoverflow, learned a lot here. Upfront, I am a hobbist learning day by day.

I have bash script which works so far one time. Let me explain in short what it does.

I am logging my "application" into tmp file jctl. This application logs changes within a system if a URL request is changing by user action and adding it into jctl as long log entry. Then with a combination of grep/tail I finally filter the usable URL which is my variable "var0". Means "var0" is changing from time to time. Three conditions are possible

• var0 URL is equal - do nothing
• var0 URL has changed - kill running ffmpeg and restart ffmpeg with new URL from var0
• var0 is empty - kill running ffmpeg and wait for new URL from var0

The while true loop generating var0 is working, the part of handover to ffmpeg , start/stop ffmpeg does work one time, when I start the script. When var0 changes or is empty the URL started with script first time is executed.

Expected behavior is: The while loop runs inifinte, updates variable var0 based on the logs in jctl file, and start/stops ffmpeg according the var0 criteria described above.

I hope anyone can help or give the right hint. Thanks in advance.

What it does: It fetches on demand a HLSv5 manifest with separate Video and Audio m3u8 and ffmpeg muxes them to one mpgets stream.

My scrip开发者_StackOverflow中文版t so far:

#!/bin/sh

journalctl -fu application -o cat > /tmp/jctl &

while true
do
  cat /tmp/jctl | grep "playing" | tail -n1 | tee /tmp/all

  grep -Eo "(prox/http|prox/https)%3a//\[a-zA-Z0-9./?=\_%:-\]\*(:)" /tmp/all |
    tail -n1 | sed 's,:,,g' | sed 's,prox/https%3a,https:,g' | tee /tmp/var0

  var0=$(sed -n "1p" /tmp/var0)
  if [ ! -z "$var0" ] # URL not empty
  then
    curl -L $var0 | tee /tmp/tmp
    var1=$(sed -n '/RESOLUTION=1/{n;p}' /tmp/tmp | sed -n "1p")
    var2=$(sed '/DEFAULT=YES[^[]*URI="/!d;s//&\n/;s/.*\n//;:a;/"/bb;$!{n;ba};:b;s//\n&/;P;D' /tmp/tmp | sed -n "1p")
    `ffmpeg -re -rtbufsize 8M -i $var1 -i $var2 -c copy -f mpegts udp://227.0.0.1:1234?pkt_size=1316 &`
  fi
done  

---

To be able to kill ffmpeg command you have to get it pid, grep it or better store it in special var at the moment of running ffmpeg in bg, like this:

ffmpeg -re ... 1316 & ffmpeg_pid=$!

$ffmpeg_pid var will store your ffmpeg command's pid.

kill $ffmpeg_pid

And to check that url changed you have to store previous value somewhere, so when you get $var0 store it in $old_url var for example and than check:

[[ $var0 != $old_url ]] && echo 'url changed'