I'm writing a module to (I hope) efficiently parse large logfiles with a variable entry length (most of the log entries are more than one line, some several hundred lines long). With each log entry I also need to extract the time/date.

As I go about it right now I have a regular expression matching the beginning of each log entry, with parenthisized subexpressions capturing year, day, month, hour, minute and second of the entry.

I load a chunk of the logfile in question into $_, using sysread. Then I split this into log entries, and subexpressions and put it into an array local to my module. The array looks like this: 

    [
        [ "LOGENTRY 1", $1, $2, $3, $4..],
        [ "LOGENTRY 2", $1, $2, $3, $4..],
        ...
    ]

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Each subsequent call to my module's next_entry() simply shifts the top element off the array and return that, until there's only one element left -- then I add another chunk from the logfile, splits that into an array-of-arrays and start the whole circus over again.

However, I'm having some problems in the logfile chunk parsing. Right now, it looks like this: 

while (/$regex/g) {
    push @buffer, [
        substr($_, $last, $-[0]-$last),
        $1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12,
    ];
    $last = $-[0];
}

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At first I tried 

while (@x = /($regex)/g) {
    push @buffer, [ @x ];
}

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..but to my suprise that didn't work. Turns out that the m//g in list context returns one list of all subexpressions matched, rather than (as m// without the /g flag) one list of subexpressions per match.

How should I go about this? Perhaps there's some better method that I have completely missed?

P.S. Note that my regex does not match an *entire* log entry, just the beginning of it.

In reply to Efficient log parsing? by zrajm

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