prepend timestamp to continiously updating log file

Shell Programming and Scripting
1

Hi,

I have a process which outputs to a log.

Below is the code snippet:

 
process   &> $LOGFILE&

The log file keeps on updating whenever a transaction is processed.
The log file has a time stamp added so every time I kill the process and start the process a new log file is created with latest time stamp.

Because the log file would be growing forever, I would like to prepend time stamp for each line in the log file. I used the below way but instead of writing the log every time a transaction is processed, the time stamp is added to each line in the log after the kill the process.

 
process  | sed "s/^/$(date)/" &> $LOGFILE&

Can you let me know how do I prepend time stamp inside the log in real time?

Thank you!

2

You don't... I can't think of an effective way to do this which doesn't involve fixing the application to do what you want in the first place.

If you must 'intercept' the log, make a new log, don't keep editing the old one in place. How many thousands of times will the application be killed to do it your way?

tail -f logfile | while read LINE
do
        echo $(date) "$LINE"
done > newlogfile
3

@Corona688 - Your solution works if the log file which you took as input is already created. But in this case, the log file will be updating always whenever a transaction is processed.

Also, per your suggestion, I need to create another log file which I do not want to.

I want to create only once when the process runs and output the detail of process to log with time stamp before each line.

FYI, the command is inside a shell script and all this is desired when the script is executed.

And, I will be killing the process may be once in a day.

4

I badly misunderstood what you were saying, my apologies.

My suggestion would still function with a little modification however.

process | while read LINE
do
        echo "$(date) $LINE"
done > outputfile

Anything involving pipes may buffer unexpectedly, however; collecting lines until the buffer fills and you get a bunch of lines at once. Behavior may depend on your system, try it and see.

5

Thanks Corona688

It worked. I'll do some tests and see if there are any issues with pipes.

1 Like