C:\test>p1
[0] Perl> $str = join'', 'a'..'z',0..9,'A'..'Z';;
[0] Perl> @fields = (
  [ name1 => { start =>  0, len=> 10 } ],
  [ name2 => { start =>  8, len=>  3 } ],
  [ name3 => { start => 11, len=> 14 } ],
);;

## This one line does all the work!
[0] Perl> @bits = map{ substr $str, $_->[1]{start}, $_->[1]{len} } @fields;;

[0] Perl> print for @bits;;
abcdefghij
ijk
lmnopqrstuvwxy