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

My question is similar to this one, but I'm pretty much a newbie so I have a question in addition: I understand how to throw a file line-by-line into an array, but how could I search the array for "Down" in one element and "Up" in a following (not necessarily the next) element? I'm trying to generate stats from a router log that looks something like this: 
a_time_down  Down
a_time_up    Up
a_time_down  Down
a_time_down  Down
a_time_up    Up

[download]
I have to come up with a aggregate downtime from a log like this. I found Time::ParseDate (what a blessing!), so once I know which Down element cooresponds with the next Up, tallying up the downtime shouldn't be a problem. Thanks so much for your help; I'm pretty new to Perl so please be kind. :)

Replies are listed 'Best First'.
Re: How do I parse and evaluate a file line-by-line?
by Trimbach (Curate) on Mar 03, 2001 at 08:39 UTC
    Here's one quick solution: 
    #!/usr/bin/perl -w

use strict;
my $last = "";
my $cursor = -1;
my @output;

while (<DATA>) {
    my ($time, $switch) = split "\t";
    if ($switch eq $last) {
        $output[$cursor] = $_;
    } else {
       $cursor++;
       $output[$cursor] = $_;
       $last = $switch;
    }
}

foreach (@output) {
    print;
}


__DATA__
time1    UP
time2    DOWN
time3    UP
time4    DOWN
time5    DOWN
time6    DOWN
time7    UP
time8    UP
time9    UP
time10    DOWN
time11    UP

    [download]
    The idea here is to record just the last "UP" or "DOWN" event in a string of one or more "UP" or "DOWN" events. $cursor is used to keep our place in the array, overwritting successive UP's and DOWN's as necessary.

    Gary Blackburn
    Trained Killer

[reply]
[d/l]
      You can tighten that middle loop up a bit by getting out of "C think" and getting into "Perl think": 
      while (<DATA>) {
  my ($time, $switch) = split "\t";
  if ($switch eq $last) {
    $output[-1] = $_;
  } else {
    push @output, $_;
    $last = $switch;
  }
}

      [download]
      The $cursor variable is unnecessary, because Perl always knows how long the array is.

      -- Randal L. Schwartz, Perl hacker

[reply]
[d/l]
        Thanks for that... I rarely use $array[$element] to grow an array, preferring "push", but I couldn't use push indiscriminately here because I needed to write over successive instances of UP or DOWN. Of course, $array[-1] was exactly what I was looking for. Gotta get used to using the relative position in an array....

        And for the record, it wasn't "C think" as I actually know absolutely nothing about C. It was just inexperience. :-D

        Gary Blackburn
        Trained Killer

[reply]
[d/l]
[select]
Re: How do I parse and evaluate a file line-by-line?
by Tuna (Friar) on Mar 03, 2001 at 08:55 UTC
    one way is like this: 
    #!/usr/bin/perl -w

use strict;
my $file = "/home/trix/lines";
my $line;
my @array;

open (FILE, "$file") || die "Can't open $file: $!\n";

while ($line = <FILE>) {
chomp $line;
next unless ($line =~ /Down/);
my ($downtime, $down) = split(' ', $line);
push (@array, $downtime);

}
my $agg = eval join '+', @array;
 
  #the above beauty came from somewhere here; don't remember where

print "My downtime is $agg\n";

    [download]
    ....if I am understanding correctly that the first element in each log file is actually a number, and there is only one other element, the interesting one being "Down".
[reply]
[d/l]

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