I have an external program which I can not edit. It writes its log to a file.
How do I add a timestamp to each line while the program writes to the logfile?
It does not write its output to stdout. The timestamp should at least include seconds. Preferably only using standard linux tools such as pipes, bash, cron etc.
After testing a few example scripts, I noticed that the program closes the logfile to reload its configuration, then it recreates the same file as a plain empty textfile. I guess this means one has to use another approach such as continously (cron) rechecking the file contents?