Use Tie::File. Try something like this:

use Tie::File;

$YOUR_LOG_LINE = "whatever you want.\n";

my @log;  
my $o = tie @log, 'Tie::File', 'log.dat' or die $!;

$o->flock;                       # Default is conveniently LOCK_EX

unshift @log, $YOUR_LOG_LINE;    # Add line to beginning. 
$#log = 99 unless @log < 100;    # Truncate to 100 lines if necessary.
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But, no. That won't work with perl4. Upgrade. Everyone's doing it. ;-)

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