my $count =0;
LINE: while(<DATA>)
{
   next LINE unless /^E/../^G/; # next line unless we are between a line starting with a end a line starting with G
   die "Oups, went too far!" if /^h/; # error if the line starts with an h and hasn't been skipped by the previous statment
   $count++ unless /^G/; # count that do not start with a G
}

__DATA__
Q165HWN0X001
Q165HWN0X002
Q165HWN0X003
E99HEADER|006|001
E99INSSCH|052|
E99POLCOM|1||IIL|62|35119849249024|||||
E99INSFAC2|C00124||||||XAJX0727,YGAX0000,ZAAJ0203,VABA0018,WJZA1800|
G35119849249024
h189SMA2