# real important!
use strict;
use warnings;

# this is the file where the data is
my $file = 'path_to_file';

# these are some useful variables
my $sum = 0;
my $lines = 0;
my $avgerage;

# open file
open(FH, $file) or die "File $file failed to open:";

#read file in line by line
while(<FH>) {
  # get the third column and add it to $sum
  $sum += (split /\s+/, $_)[2];
  # update $lines
  $lines++;
}

# now, to get the average, all you do is say
$average = $sum/$lines;
[download]

you could try something like:

#! /opt/local/bin/perl -w

# I recommend the strict pragma if you are new to perl
use strict;

# you could get the data you provided into an array in any
# number of ways.
my @data = ("1234-5678 12 .345678", "1234-5678 90 .123456");
my $sum;

foreach (@data) {
    # puts each piece of information into its own variable
    # in case you need to use them for something.
    # you could push them into arrays to keep track of them
    my ($user_id, $proc_id, $time) = split();

    # adds the time from the current line to the running
    # total of time values
    $sum += $time;
}

# divides the total times by the total number of times 
# (the index of the last element in the array + 1)
my $average = $sum/($#data + 1);

print $average;
[download]

that is probably much longer than it needs to be, but it worked when I tested it on your data.

good luck!
--au

update: bah! not only did Dimmesdale beat me to it, he had comments too! added comments.

Smells like homework.. . .

-Any sufficiently advanced technology is
indistinguishable from doubletalk.

my %procid;
my %procidcount;

open (FILE, "file");

while (<FILE>) {
   my ($id, $keystroke, $seconds) = split / /;
   $procid{"$id"} += $seconds;
   ($procidcount{"$id"})++
}

foreach my $ids (sort keys %procid) {
        printf "Average for $ids is %f...\n", $procid{"$ids"} / $proci
+dcount{"$ids"};
}
[download]

1234-5678 12 .345678
1234-5678 90 .123456
1234-5674 12 .345678
1234-5674 90 .123456
1234-5674 12 .345678
[download]

Average for 1234-5674 is 0.271604...
Average for 1234-5678 is 0.234567...
[download]

awk '{s += $3} END { print s/NR }' data.txt
[download]

Anything awk can do...

perl -lane '$s+=$F[2]}{print $s/$.'

-sauoq
"My two cents aren't worth a dime.";

okay, i'll bite. why does this work?

I mean, using an explicit END block i understand...

perl -lane '$s+=$F[2]; END{print $s/$.;}'

But what is it about your "}{" that makes the print part of an implicit END block? Is this documented behavior? or an unintenional artifact of the way the parser deals with -n ?