Execute command in bash script until output exceeds a certain value

I am using a command that parses video files for specific frames and returns their timecode when found. At this point I need to execute a command, wait until the values ​​printed to stdout reach the desired position, then abort execution with Ctrl+ C.

How am I supposed to monitor the process and interrupt execution at the right time to get the information I want, I thought I could automate this to some extent by creating a bash script.

I'm not sure if this can be done in bash, as I don't know exactly how to abort execution due to the values ​​it writes to stdout.

The command output looks like

0.040000
5.040000
10.040000
15.040000
18.060000
(...)

      

        
        
        
      

    

I tried

until [[ "$timecode" -gt 30 ]]; do
  timecode=$(mycommand)
  sleep 0.1
done

echo "Result: $timecode"

      

        
        
        
      

    

or

while [[ "$timecode" -le 30 ]]; do
  timecode=$(mycommand)
  sleep 0.1
done

echo "Result: $timecode"

      

        
        
        
      

    

which appear to cause the command to run until it finishes, and then the rest of the loop is processed. But I want to evaluate the result while the command is executing and aborting depending on the output.

Additional Information

The command cannot be stopped at a certain point in the flow. It analyzes the entire file and gives results if not stopped. This was my first shot.

The command execution time is very long as the files I am looking at are ~ 2GB. Since I don't want all the frames of the file, but only some of them at a given timecode, I never let it execute until it finishes.

The output of the command varies from file to file, so I cannot find the exact value. If I knew the exact meaning, I probably wouldn't have to look for it.

The destination time code - in the example given by "-gt 30" - is different for every file I will need to parse, so I will have to put it in a command line parameter after the script is running, I would also have to make sure that will return more than the last execution value, but about the last 5 values. For these two, I already have ideas.

I'm completely stuck with this and don't even know what to do on google.

Thanks for your input!

Manuel

With the answers from PSkocik and Kyle Burton, I was able to integrate the proposed solution into my script. It doesn't work and I can't see why.

Here's the complete script, including an external command providing the output:

 #!/usr/bin/env bash
 set -eu -o pipefail

 parser () {
   local max="$1"
   local max_int

   max_int="${max%.*}"

   while read tc;
     do
       local tc_int
       tc_int="${tc%.*}"
       echo $tc

       if (( "$tc_int" >= "$max_int" )); then
         echo "Over 30: $tc";
         exec 0>&-
         return 0
       fi

     done
 }

 ffprobe "$1" -hide_banner -select_streams v -show_entries frame=key_frame,best_effort_timestamp_time -of csv=nk=1:p=0:s="|" -v quiet | sed -ne "s/^1|//p" | parser 30

      

        
        
        
      

    

I am not getting any output from "echo $ tc", but ffprobe works - I can see it from above. It works until I stop the script using Ctrl+ C.

Thanks to Kyle for your great efforts in this. I never came to that conclusion. I changed the ffprobe command line to your suggestion

 ffprobe "$1" -hide_banner -select_streams v -show_entries frame=key_frame,best_effort_timestamp_time -of csv=nk=1:p=0:s="|" -v quiet | cut -f2 -d\| | parser 30

      

        
        
        
      

    

and now, I get the results while ffprobe is running. But ... the way you changed the command returns all frames, ffprobe finds and not just keyframes. The original output of the ffprobe command looks like

 1|0.000000
 0|0.040000
 0|0.080000
 0|0.120000
 0|0.160000
 0|0.200000
 (...)

      

        
        
        
      

    

0 at the beginning of the line means: this is not a keyframe. The 1 at the beginning of the line means: this is a keyframe.

The script is meant to only provide keyframes around a specific timecode of a video file. The way you changed the command now exposes all frames of the video file, making the result useless as a result. It must be filtered for all zero-based lines to be deleted.

As I don't quite understand why this doesn't work with sed, I can only try to find a solution through try and error, making it easier for various tools to filter the output. But if the filtering itself is causing the problem, we could hit the wall.