Create a unique key from the tid/pid by extracting those values from the log file (e.g. with a regex match), and then use a hash to count those keys' occurrences: $count{$key}++; (by iterating over the lines of the file)

what i have tried is this--

#!/usr/bin/perl -w

print "Hello, World...\n";
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;
my $TIDCount = 0;
while(my $line = <$log>) { 
    # Outer loop. Look for an interesting part of the log file. 
    $n++; 
    $line =~ tr/\r\n//d; 
    if($line =~ /tid (\d+)/){
        $TIDCount++;
        next;
    }
}
print "Thread count for the logfile is $TIDCount\n";
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but it is giving me the whole count including the repated ones, but i just want the count of unique threads. Thanks NT

Did you read almut's post. There is a big clue in it, if you capture the digits after 'tld ', which you do, you can assign them to a value, if you put the scalar into a list context with brackets

my $substring;
my $string="For those about to rock";
($substring)=$string=~/^.+?to (\w+)/;
print "So, we're going to $substring then?\n";
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using this type of structure you can identify specific threads, then if you increment $threads{$substring} you have an array  keys %threads which contains the thread id of each thread, you even have a count of how busy they are in the logfiles ;)