>perl -wMstrict -le
"my @text = qw/A B C D E F G H F I J/;
 ;;
 my @F_in_it = grep { $text[$_] eq 'F' } 0 .. $#text;
 ;;
 print qq{these indices have an 'F': @F_in_it};
"
these indices have an 'F': 5 8