123 aBVXC   SAOMEWTRINOGN   ABC
876 AsrdaDS some_bs 564
37897654    aofruafdouf abc
<c>

<c>
#!/usr/bin/perl -w
use strict;

open (IN, '<', "tab_file.txt") or die "$!";
while (<IN>)
{
   my ($first_token) = split (/\s/, $_); #should be(/\t/, $_)
   print $first_token,"\n";
}

__END__
123
876
37897654

tab_file.txt: (not really tabs)...

123 aBVXC   SAOMEWTRINOGN   ABC
876 AsrdaDS some_bs 564
37897654    aofruafdouf abc