johngg@shiraz:~ > perl -Mstrict -Mwarnings -E '
my $find = q{thispart};
say $find;
my $str  = q{ksguhdipghisosipghthispartudirlhgdr};
say $str;
my $posn = index $str, $find;
die qq{Substring not found\n}
   if $posn == -1;
my $idNo = substr $str, $posn, length $find, q{};
say $idNo;
say $str;'
thispart
ksguhdipghisosipghthispartudirlhgdr
thispart
ksguhdipghisosipghudirlhgdr

##</code><code>##

johngg@shiraz:~ > perl -Mstrict -Mwarnings -E '
my $find = q{thatpart};
say $find;
my $str  = q{ksguhdipghisosipghthispartudirlhgdr};
say $str;
my $posn = index $str, $find;
die qq{Substring not found\n}
   if $posn == -1;
my $idNo = substr $str, $posn, length $find, q{};
say $idNo;
say $str;'
thatpart
ksguhdipghisosipghthispartudirlhgdr
Substring not found

##</code><code>##

johngg@shiraz:~ > perl -Mstrict -Mwarnings -MData::Dumper -E '
my $idStr = q{381980767204};
my %idLookup =
   map { $_ => 1 }
   unpack q{(a4)*}, $idStr;
print Data::Dumper->Dumpxs( [ \ %idLookup ], [ qw{ *idLookup } ] );
say qq{ID $_ }, exists $idLookup{ $_ } ? q{found} : q{not found}
   for qw{ 7204 6720 };'
%idLookup = (
              '8076' => 1,
              '7204' => 1,
              '3819' => 1
            );
ID 7204 found
ID 6720 not found