Use a while loop to validate the input, use subroutines for submenus. The return value of the submenu can be used to decide whether to quit or continue, i.e. back or quit.
#! /usr/bin/perl
use warnings;
use strict;
use feature qw{ say };
my $done;
while (! $done) {
print << '__MENU__';
Main Menu
1. Get date and time
2. Go to submenu
3. Quit
__MENU__
chomp( my $reply = <> );
next unless $reply =~ /^[123]$/;
if ($reply == 1) {
say scalar localtime;
} elsif ($reply == 2) {
$done = submenu();
} else {
$done = 1;
}
}
sub submenu {
my $done;
while (! $done) {
print << '__MENU__';
Submenu
1. Get username
2. Back
3. Quit
__MENU__
chomp( my $reply = <> );
next unless $reply =~ /^[123]$/;
if ($reply == 1) {
say scalar getpwuid $>;
} else {
$done = $reply;
}
}
return $done == 3
}
As you probably noticed, most of the code is repeated, so it should be extracted to a subroutine.
Update:
#! /usr/bin/perl
use warnings;
use strict;
use feature qw{ say };
menu('Main Menu',
[ 'Get date and time', sub { say scalar localtime } ],
[ 'Go to submenu', sub { $_[0] = submenu() } ],
[ 'Quit', sub { $_[0] = 1 } ],
);
sub menu {
my ($title, @options) = @_;
my $done;
while (! $done) {
say $title;
say 1 + $_, ". $options[$_][0]" for 0 .. $#options;
chomp( my $reply = <> );
next unless $reply =~ /^[1-9][0-9]*$/;
next if $reply > @options;
--$reply;
$options[$reply][1]->($done, $reply);
}
return $done
}
sub submenu {
my $result = menu('Submenu',
[ 'Get username', sub { say scalar getpwuid $> } ],
[ 'Back', \&pass ],
[ 'Quit', \&pass ],
);
return $result == 2 # Propagate Quit.
}
sub pass { $_[0] = $_[1] }
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}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,