учись, мля, халявщик !

#!/usr/bin/perl

open(COM, "</dev/ttyS0") || die "Can't open ttyS0";
open(LOG, ">>path/to/my/log") || die "Can't open mylog";
while(<COM>)
{
print LOG;
}
close(LOG);
close(COM);

Save to file.pl, for example, and then type command as follow:
chmod -v u+x file.pl

;-------------------------
That's all!!!
have fun!!!

А можно и так.

cat /dev/ttyS0 >filename &

cat /dev/ttyS0 >>filename &

Примерно Вот так: int id = open(/dev/ttyS0); read(id,pchar); Могу дать 100% рабочий код.