You could solve that with substrings and lc / uc. Just compare the entered string with the a substring from the menu options, starting at 0 and having the same length your entered string has. Convert both strings to lower (or upper) case before comparing.

Or you could compare each menu string with /^$entered_string/i. But take care to quotemeta the entered string so that entering "." or ".*" doesn't confuse your program.

My first crack at this may be more comprehensible:

Basically, if the input looks like a number, it's used as an index into the array of menu items. Otherwise, it loops through the menu looking for the first thing that "matches" the input.

My rewrite made this more useful as a menu in real code. Each menu item is now a hash ref that has a reference to a sub to handle the menu item. If need be, you can add more "stuff" to each hash ref. For example, maybe instead of substrings, you want to have regular expressions match the user's input. In that case, you could have a qr// stuck on each one used in the first loop instead of lc substr.

use Scalar::Util qw( looks_like_number );
use List::Util qw( first );   

my @menu = (
    { title => 'Known star',        handler => \&load_star },
    { title => 'Create a new star', handler => \&create_star },
    { title => 'List Known Stars',  handler => \&list_stars },
    {   
        title   => 'Quit',
        handler => sub { exit }
    }
);
my $input = '...';
my $picked;
if ( looks_like_number $input ) {
    $picked = $menu[ $input - 1 ];
}
else {
    $picked = first {
        length $input <= length $_->{title}
          and lc $input eq lc substr $_->{title}, 0, length $input;
    }
    @menu;
}
if ( !defined $picked ) {
    die "What do you mean by '$input'?";
}

# "call" the menu item
$picked->{handler}->();
[download]

I am wondering if, perhaps, this page might offer a better original listing: USML / Planetary Stuff ?

Why not provide a Tk (or other) GUI instead? It needen't be all that hard. Consider:

use strict;
use warnings;
use Tk;
use Tk::DialogBox;
use Tk::Listbox;

my $mw = MainWindow->new ();
my %starData;
my @params = ($mw, \%starData, );

$mw->Button (-text => 'Known star', -command => [\&knownStar, @params]
+)->pack ();
$mw->Button (-text => 'New star', -command => [\&newStar, @params])->p
+ack ();
$mw->Button (-text => 'List stars', -command => [\&listStars, @params]
+)->pack ();
$mw->Button (-text => 'Quit', -command => [\&quit, @params])->pack ();

MainLoop ();


sub knownStar {
    my ($mw, $starData) = @_;
    my @stars = map {[split ',']} split "\n", <<STARS;
Sol, G2,1.0
Alpha Centuri A, G4,1.08
Alpha Centuri B, K1,.88
Epsilon Eridani, K2,.30
Tau Ceti, G8, .82
70 Ophiuchi A, K1,.9
70 Ophiuchi B, K5,.65
Eta Cassiopeiae A,f9,.94
Eta Cassiopeiae B,k6,.58
Sigma Draconis, G9,.82
36 Ophiuchi A, K2, .77
36 Ophiuchi B, K1,.76
Hr 7703, K2, .76
Delta Pavonis, G7,.98
82 Eridani, G5,.91
Beta Hydri, G1,1.23
Hr 8832, K3, .74
STARS
    my @names = map {$_->[0]} @stars;
    my $dlg = $mw->DialogBox (
        -title => 'Select known star',
        -default_button => 'OK',
        -buttons => ['OK', 'Cancel'],
        );
    
    my $listbox = $dlg->add ('Listbox',
        -listvariable => \@names,
        -selectmode => 'single'
        )->pack ();

    return if $dlg->Show () eq 'Cancel';

    my @sel = $listbox->curselection ();
    
    return unless @sel;
    
    print "@{$stars[$sel[0]]}\n";
    $starData->{$sel[0]} = $stars[$sel[0]];
}


sub newStar {
    my ($mw, $starData) = @_;
    
    # Generate new star data here
}


sub listStars {
    my ($mw, $starData) = @_;
}


sub quit {
    my ($mw, $starData) = @_;
    
    # Save handling here if required
    exit;
}
[download]