perl -e 'open(FILE,"./syslog") or die "Cannot open syslog: $!\n"; sleep 1000000000;' &

then

perl -i -p del.pl ./syslog


##</code><code>##

perl -e 'use Fcntl;open(FILE,"./syslog") or die "Cannot open syslog: $!\n";flock(FILE,LOCK_EX); sleep 1000000000;' &

then

perl -i -p del.pl ./syslog