perlish way to 'tail -100 $logfile'

gri6507 has asked for the wisdom of the Perl Monks concerning the following question:

Fellow monks,

I have a program that is started when a user logs into the system and stays alive (hopefully) until the user exits. This program occasionally logs some events to $logfile. Recently, I received a request from my boss to make sure that this logfile does not exceed some predefined file size, which, for the sake of this discussion will be 100 lines of the log file. In other words, I need a way to do `tail -100 $logfile > $logfile.tmp; mv $logfile.tmp $logfile` from inside my script. Is there a propper perlish way to do that?

Comment on perlish way to 'tail -100 $logfile'

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Re: perlish way to 'tail -100 $logfile' by talexb (Chancellor) on Dec 09, 2005 at 17:45 UTC
I've heard of File::Tail though I haven't used it. Alex / talexb / Toronto "Groklaw is the open-source mentality applied to legal research" ~ Linus Torvalds	[reply]
Re: perlish way to 'tail -100 $logfile' by holli (Abbot) on Dec 09, 2005 at 17:44 UTC
File::ReadBackwards holli, /regexed monk/	[reply] [d/l]
Re: perlish way to 'tail -100 $logfile' by isotope (Deacon) on Dec 09, 2005 at 18:04 UTC
Does your log need to be a rolling log that always contains the most recent entries, or can it simply be restarted whenever it gets too big? This make a difference in your approach. Your tail example leans more toward the former, while something like logrotate that just periodically clobbers (or archives) the file if it's too large would accomplish the latter and be much simpler. Update: To maintain a rolling logfile, if your program is persistent during a login session, you could simply maintain the most recent data internally (using an array of individual log entries, for example, push a new entry and shift the oldest one off), then dump the entire log to file each time it's updated. Not the best for maintaining logfile integrity, but the code would be very clean. --isotope	[reply]
Re^2: perlish way to 'tail -100 $logfile' by gri6507 (Deacon) on Dec 09, 2005 at 19:12 UTC
ideally, I would like to do a rolling log of 100 most recent entries, but I would not want to keep it in the memory because at any time during the customer's login session (during the program execution), they could want to take a look at the log file.	[reply]
Re: perlish way to 'tail -100 $logfile' by ptum (Priest) on Dec 09, 2005 at 17:45 UTC
It seems to me that you might simply want to evaluate the size of the file using stat or the -s file test operator, then conditionally mv the file based on the return from that. No good deed goes unpunished. -- (attributed to) Oscar Wilde	[reply]
Re: perlish way to 'tail -100 $logfile' by Roy Johnson (Monsignor) on Dec 09, 2005 at 18:02 UTC
If it's an option, I'd say rewrite the logging portion of your program to use Tie::File. Then you could just maintain the tied array at 100 elements and your logfile would automagically be what you wanted. Caution: Contents may have been coded under pressure.	[reply]