You'll probably want to use a hash of arrays, keyed by the initial string -- something like this:

my %lines;

while (<>)
{
    my ($key) = ( /^(\S+)/ ); # captures first token, assigns that to 
+$key
    push @{$lines{$key}}, $_;  # (update: fixed missing "}")
}

for (sort keys %lines) {
    my $nlines = scalar @{$lines{$_}};
    print "$nlines lines keyed by $_ :\n";
    print "  First line is: $lines{$_}[0]";
    print "  Last line is: $lines{$_}[$nlines-1]";
}
[download]