use strict;
use warnings;
use Fcntl qw(:flock);
use Time::localtime;
$| = 1;

my $logFile = "mainLog.LOG";
my $SEMAPHORE = '~'. $logFile . '.lck';
my $was_awaiting = 0;

sub WRITE_TO_LOGFILE();
sub READ_LOGFILE_FOR_SENDMAIL ();
sub IS_FILE_LOCKED($);
sub TIMESTAMP ();


###################################################################
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
###################################################################


print "\nWRITE TO LOGFILE .... \n";

    WRITE_TO_LOGFILE ();

print "\nWRITE TO LOGFILE .... [DONE]\n";

print "\nREAD LOGFILE FOR SENDMAIL ....       \n";

    READ_LOGFILE_FOR_SENDMAIL ();

print "\nREAD LOGFILE FOR SENDMAIL .... [DONE]\n";

###################################################################
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
###################################################################

sub WRITE_TO_LOGFILE ()
{
    open(S, ">$SEMAPHORE") or die "$SEMAPHORE: $!";
    print "[Semaphore open]\n";    
        while ( IS_FILE_LOCKED($SEMAPHORE) )
        {
            print "\r\t[Awaiting Semaphore lock]";
            $was_awaiting = 1;
        }

        if ($was_awaiting)
        {
            print "\n";
            $was_awaiting = 0;
        }

        print "\t[Semaphore lock]            \n";


        flock(S, LOCK_EX) or die "flock() failed for $SEMAPHORE: $!";
            print "\t\t[Logfile open]\n";
            open (FH, ">>$logFile") or die "Can't open $logFile: $!";
                print FH "I have written from PID ($$)::[".TIMESTAMP()
+."]::PHY-4-EXCESSIVE_ERRORS\n";
            close FH;
            print "\t\t[Logfile closed]\n";
            print "\t\tGoing to sleep...\n";
            sleep 10;
            print "\t\tWoken up...\n";
    close S;
    print "[Semaphore unlock]\n";
    print "[Semaphore closed]\n";
    unlink($SEMAPHORE);
}

sub READ_LOGFILE_FOR_SENDMAIL ()
{
    open(S, ">$SEMAPHORE") or die "$SEMAPHORE: $!";
    print "[Semaphore open]\n";    
        while ( IS_FILE_LOCKED($SEMAPHORE) )
        {
            print "\r\t[Awaiting Semaphore lock]";
            $was_awaiting = 1;
        }

        if ($was_awaiting)
        {
            print "\n";
            $was_awaiting = 0;
        }

        print "\t[Semaphore lock]            \n";


        flock(S, LOCK_EX) or die "flock() failed for $SEMAPHORE: $!";
            print "\t\t[Logfile open]\n";
            open (FH, "<$logFile") or die "Can't open $logFile: $!";
            open (FHT, ">", '~'."$logFile") or die "Can't open temp $l
+ogFile: $!";
            
                while(<FH>)
                {
                    chomp;
                    if ($_ =~ m/PHY-4-EXCESSIVE_ERRORS/)
                    {
                        ## SENDMAIL()
                        $_ =~ s/PHY-4-EXCESSIVE_ERRORS/PHY_4_EXCESSIVE
+-ERRORS -- SENDMAIL SENT/g;
                        print FHT "$_\n";
                    }
                    else
                    {
                        print FHT "$_\n";
                    }
                }                

            close FH;
            close FHT;

            unlink($logFile);            ## DELETE PREVIOUS LOGFILE
            rename('~'."$logFile",$logFile);        ## RENAME TEMP LOG
+FILE TO REPLACE PREVIOUS LOG FILE

            print "\t\t[Logfile closed]\n";
    close S;
    print "[Semaphore unlock]\n";
    print "[Semaphore closed]\n";
    unlink($SEMAPHORE);
}

sub IS_FILE_LOCKED ($)
{
    my $theFile;
    my $theRC;

    ($theFile) = @_;
    $theRC = open(my $HANDLE, ">>", $theFile);
    $theRC = flock($HANDLE, LOCK_EX|LOCK_NB);
    close($HANDLE);
    return !$theRC;
}

sub TIMESTAMP ()
{
    my $t = localtime;
    return sprintf( "%04d-%02d-%02d_%02d-%02d-%02d",
             $t->year + 1900, $t->mon + 1, $t->mday,
             $t->hour, $t->min, $t->sec );
}

__END__

-RUNTIME-

    C:\monks>perl loggie.pl

    WRITE TO LOGFILE ....
    [Semaphore open]
        [Semaphore lock]
            [Logfile open]
            [Logfile closed]
            Going to sleep...
            Woken up...
    [Semaphore unlock]
    [Semaphore closed]

    WRITE TO LOGFILE .... [DONE]

    READ LOGFILE FOR SENDMAIL ....
    [Semaphore open]
        [Semaphore lock]
            [Logfile open]
            [Logfile closed]
    [Semaphore unlock]
    [Semaphore closed]

    READ LOGFILE FOR SENDMAIL .... [DONE]

    C:\monks>


- Log File -

    I have written from PID (7892)::[2013-11-19_11-52-41]::PHY_4_EXCES
+SIVE-ERRORS -- SENDMAIL SENT
    I have written from PID (7452)::[2013-11-19_11-53-33]::PHY_4_EXCES
+SIVE-ERRORS -- SENDMAIL SENT
[download]