my $str = 'somewords';
local ($\,$,) = ("\n") x 2;
print map {substr $str, 0, $_} 1..length($str);
# or
print map {$str =~ /(.{$_})/} 1..length($str);
# or
{
  my $mem;
  print map {$mem .= $_} split //, $str;
}
# etc. (Golf?)