my $sequence_number = shift || die ...;
# technically, you want 'or' instead of '||' here

open (ERROR, "/usr/bin/errpt -g -l $sequence_number |");
# you don't check to see if it opened properly...
# nor do you ensure the safety of the variable
# if I enter '; rm -rf' here, you're in trouble


my ($sequence_number) = shift =~ /(\d+)/
  or die ...;
open ERROR, "/usr/bin/errpt -g -l $sequence_number |"
  or die "can't run errpt -g -l $sequence_number: $!";