How can I turn a string into a variable name?

mnooning has asked for the wisdom of the Perl Monks concerning the following question:

I want to check if more than one of the many GetOptions options were used, and I want to know which ones were used. More than one is not allowed. For a quick check, I tried with only three options. In the code below, which does NOT work, only the "two" should match.

use strict;

my $one = 0;
my $two = 1;
my $three = 0;

my @strings = qw (one two three);
my @optionsToCheck = ($one, $two, $three);

foreach my $string (@strings) {
    print "Option $string was used\n" if ( ${"$string"} );
}
[download]

I tried different variations, but could not seem to get it. I could use a key/value hash, but that seems overkill. Besides, if I added or took away options, I'd have to remember to change the hash, too. I suspect Perl has a simple answer, but I cannot see it.

Thanks

Comment on How can I turn a string into a variable name? Download Code

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Re: How can I turn a string into a variable name? by ikegami (Patriarch) on Jan 09, 2010 at 19:13 UTC
Don't. `GetOptions( '--one' => \$one, '--two' => \$two, '--three' => \$three, ); die "Only one of options --one, --two and --three are allowed\n" if ( grep defined, $one, $two, $three ) > 1;` [download] or `GetOptions( '--one' => \$opts{one}, '--two' => \$opts{two}, '--three' => \$opts{tree}, ); die "Only one of options @{[ sort keys %opts ]} are allowed\n" if ( grep defined, values(%opts) ) > 1;` [download] Update: Updated since I hadn't properly read the question initially.	[reply] [d/l] [select]
Re: How can I turn a string into a variable name? by chromatic (Archbishop) on Jan 09, 2010 at 19:15 UTC
If you really cannot use a hash (and that's easily the best way to do this), install PadWalker and use `my $lexicals = peek_my(0);` to get a hash reference which you can use to manipulate all lexical variables bound to the current scope. (If manipulating Perl 5 internals from pure Perl still seems less overkill than using a hash, consider that `PadWalker` can read from and write to and even create lexicals in other scopes, ignoring encapsulation.)	[reply] [d/l] [select]
Re^2: How can I turn a string into a variable name? by Anonymous Monk on Jan 09, 2010 at 20:32 UTC
I can use a hash. It looks like that is what I will do. I was just hoping for a slicker way. Thanks	[reply]
Re: How can I turn a string into a variable name? by almut (Canon) on Jan 09, 2010 at 19:27 UTC
In theory, you could write `print "Option $string was used\n" if ( eval "\$$string" );` [download] But, as already said, don't. eval in this context is definitely worse than using a hash, in almost every regard.	[reply] [d/l]
Re^2: How can I turn a string into a variable name? by ikegami (Patriarch) on Jan 09, 2010 at 20:08 UTC
Why use `eval` to do `if do { no strict 'refs'; $$string };` [download]	[reply] [d/l] [select]
Re^3: How can I turn a string into a variable name? by almut (Canon) on Jan 09, 2010 at 20:21 UTC
Why use `eval` ...because the OP used lexical variables. Symbolic references (`$$string`) only work with package variables.	[reply] [d/l] [select]
Re: How can I turn a string into a variable name? by GrandFather (Saint) on Jan 09, 2010 at 21:58 UTC
Where do the 'options' come from? If they are from the command line use Getopt::Long. If they are derived internally (perhaps through a GUI or command line interface) then you could: `use strict; use warnings; my %options = map {$_ => 0} qw(one two three); $options{two} = 1; # Set in some unspecified place for my $option (grep {$options{$_}} keys %options) { print "Option '$option' was used\n"; }` [download] Prints: `Option 'two' was used` [download] True laziness is hard work	[reply] [d/l] [select]