How can match the first value of #ARGV to an array of possible options - perl

Question

I am trying to figure a way to capture the first argument from #ARGV and check its validity by checking it against an array of known valid arguments. I thought I could do this with a simple foreach loop but I realized this won't work because it will fail when the first invalid match comes back, which for my example script is the second argument.
Here the code that pertains to the problem, its concept script so there is not much.
my $primary_mode = $ARGV[0];
primary_mode_check($primary_mode);
sub primary_mode_check {
my #program_modes = ('create', 'destroy');
my $selected_mode = shift;
foreach my $mode (#program_modes) {
if ($selected_mode ne $mode) {
die RED "\'$selected_mode\' is not a valid program mode!\n";
}
}
}
Is there another way to accomplish the same idea? I am already using Getopt::Long in combonation with #ARGV to achieve a certain style. So I am focused on wanting to make this work.
UPDATE
I was thinking maybe I could match against regex, is that a possibility?

Answer 1

my $primary_mode = $ARGV[0] or die "No mode provided";
primary_mode_check($primary_mode);
sub primary_mode_check {
my $selected_mode = shift;
my #program_modes = ('create', 'destroy');
die "'$selected_mode' is not a valid program mode!\n"
unless grep { $selected_mode eq $_ } #program_modes;
}
If you are using perl 5.10 or greater:
use v5.10;
my $primary_mode = $ARGV[0] or die "No mode provided";
my #program_modes = qw(create destroy);
die "'$selected_mode' is not a valid program mode!\n"
unless $primary_mode ~~ #program_modes;

Answer 2

You code: Die if the arg doesn't match one of the allowed modes.
You want: Die if the arg doesn't match any of the allowed modes.
Put differently: Don't die if the arg matches one of the allowed modes.
my #program_modes = qw( create destroy );
sub primary_mode_check {
my ($selected_mode) = #_;
for my $mode (#program_modes) {
return if $selected_mode eq $mode;
}
die "'$selected_mode' is not a valid program mode!\n";
}
But a hash simplifies things a bit.
my %program_modes = map { $_ => 1 } qw( create destroy );
sub primary_mode_check {
my ($selected_mode) = #_;
die "'$selected_mode' is not a valid program mode!\n"
if !$program_modes{$selected_mode};
}

Answer 3

You might find App::Cmd useful for easy writing of application with commands.

Answer 4

I would recommend going with a hash of allowed modes. In addition, pass the allowed modes to the function rather than embedding them in the function.
You can also use grep for this purpose if the allowed modes are in an array:
#!/usr/bin/env perl
use warnings; use strict;
my ($primary_mode) = #ARGV;
my $allowed_modes = [qw(create destroy)];
check_primary_mode($primary_mode, $allowed_modes)
or die sprintf "%s is not a valid program mode\n", $primary_mode;
sub check_primary_mode {
my ($mode, $allowed) = #_;
return grep $mode eq $_, #$allowed;
}
However, grep will go through the entire array even though we need just one match. List::MoreUtils::first_index will short-circuit once a match is found (it does not matter if you have only two possible modes, but in the more general case, it might):
use List::MoreUtils qw( first_index );
...
sub check_primary_mode {
my ($mode, $allowed) = #_;
return (0 <= first_index { $mode eq $_ } #$allowed);
}

Answer 5

my $primary_mode = $ARGV[0];
primary_mode_check($primary_mode);
sub primary_mode_check {
my %program_modes; #program_modes{qw(create destroy)}=();
my $selected_mode = shift;
die RED "\'$selected_mode\' is not a valid program mode!\n"
unless exists $program_modes{$selected_mode};
}

Answer 6

I often use this idiom in such a case:
use strict;
use warnings;
my $cmd = shift #ARGV;
my #allowed = qw/ install uninstall check purge /;
die "Cannot understand command" unless ( grep { $cmd eq $_ } #allowed );
Edit: reading more carefully it looks quite a bit like Sinan's, and he's right, using first would search faster in a large list of possible ops.

Answer 7

Yes, a regular expression should work. For example:
my #modes = ('create', 'destroy');
my $regexp = join "|", #modes;
if ($selected =~ /^(?:$regexp)\z/) {
print "Found program mode '$1'\n";
} else {
die RED "\'$selected\' is not a valid program mode!\n";
}