> Darn it, now you have me playing Perl Golf ...
Fore!
#!/usr/bin/perl -na
$k = shift @F; print "$k $_\n" for @F
Mine doesn't care about the contents of the fields, only the positions.
Neither yours nor mine will handle the input below, which the OP asked
about in response to another suggestion.
Here's a version that will work for lines having only a number:
#!/usr/bin/perl -na
$k = shift @F; print "$k $_\n" for @F ? @F : ''
--input--
1 E E E
2 C D
6
3 B E D
4 C E D
5 D E
--output--
1 E
1 E
1 E
2 C
2 D
6
3 B
3 E
3 D
4 C
4 E
4 D
5 D
5 E