use warnings;
use strict;

my $find = qr/
                ^           # start of string
                \w+         # one or more word chars (last name)
                \s+         # one or more whitespace
                (           # begin capture (goes into $1)
                  (?:H0|HT) # H0 or HT
                  .*        # everything to end of string
                )           # end capture
             /x;

open my $fh, '<', 'in.txt' or die $!;

while (<$fh>){
    if (/$find/){
        my $string = $1;    # $1 contains what we captured in the rex
        print "$string\n";
    }
}

##</code><code>##

HT00000000    I
HT00000000    S
HT00000000    I
HT00000000    M
HT00000000    I
HT00000000    I
H000000000    I
H000000000    O
H000000000    I