pgcollect: option to use PID and timestamp of started/attached process as part of the output file

[GitMensch]

Scenario:

there's a "runner script" already that executes the executable after setting up some environment variables; I've added an environment variable in front of it, that allows to "only" export the variable to pgcollect; while this works in general there's again the need to set the variable (in this case possibly the login script) and it is harder than necessary to set the a useful output file name...

Originally posted by @GitMensch in #23 (comment)

To solve this I'd like to have either replace options in the specified filename or extra flags to say "add the current timestamp and/or pid to the output name specified.

That would mean something like one of those:

pgcollect filename.pgdata -P-T -- command options
# would result in filename.pgdata.PidOfThatProcesss.CurrentTimeStamp
pgcollect filename.%T-%P.pgdata -- command options
# would result in filename.CurrentTimeStamp-PidOfThatProcesss.pgdata

(and should also work if -p PID is used)

[ostash]

If you have wrapper runner script, than you can add timestamp to the output file on your own easily. While I will have to do something with forked processes and create separate reports for them, this will be the task for pgreport, not for pgcollect.