#!/usr/bin/perl 
 
use strict; 
use warnings; 
no warnings "uninitialized"; 
 
my $logFile = $ARGV[0]; 
die "usage: $0 <logFile>" unless $logFile; 
die "Logfile $logFile doesn't exist" unless -f "$logFile"; 
open(my $log, "<", $logFile) or die "Can't open $logFile for reading."; 
print "Processing file $logFile...\n"; 
my $authenticates = {}; 
my $n = 0; 
while(my $line = <$log>) { 
    # Outer loop. Look for an interesting part of the log file. 
    $n++; 
    $line =~ tr/\r\n//d; 
    if ( $line =~ /Entering (\S+)::authenticate/ ) { 
        # Aha! Start of the interesting part. 
        my $authentication = $1; 
        while ( $line = <$log> ) { 
            # Inner loop: Find the UserName. 
            $n++; 
            $line =~ tr/\r\n//d; 
            if ( $line =~ /userName :[[](\S*)[]]/ ) { 
                my $userName = "$1" ? "$1" : "NULL";  # You have some null userNames in your log. 
                my $nSessions = $authenticates->{$authentication}->{$userName}; 
                $nSessions = $nSessions ? $nSessions += 1 : 1; # Tabulate the number of sessions for this authMethod/userName. 
                $authenticates->{$authentication}->{"$userName"} = $nSessions; 
                last; 
            } elsif ( $line =~ /(?:Entering|Exiting) \S+::authenticate/ ) { 
                print "ERROR: Misparse at line $n of $logFile\n"; 
                last; 
            } 
        } 
    } 
} 
close($log); 
 
# Output global results: 
print "AuthMethod\tUser\tSessions\n"; 
for my $authMethod (sort(keys(%$authenticates))) { 
    for my $user (sort(keys(%{$authenticates->{$authMethod}}))) { 
        print "$authMethod\t$user\t$authenticates->{$authMethod}->{$user}\n"; 
    } 
}

Processing file logfile.txt... 
AuthMethod      User    Sessions 
QnAModule       01018603        3 
QnAModule       01214225        2 
QnAModule       01789302        1 
QnAModule       NULL    2