No need to test the shift in a loop.

$ perl -le '
> sub isname { return 1 if $_[ 0 ] =~ m{(?i)^(?:bill|fred)$} }
> @a = qw{ apple peach fred };
> sub alter 
> {
>     my @new =
>        map  { uc }
>        grep { isname( $_ ) }
>        map  { my $w = shift }
>        0 .. $#_;
> }
> @A = alter( @a );
> print for @A;'
FRED
$
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I hope this is of interest.