Php – Does Perl have PHP-like dynamic variables

dynamicperlphpvariables

In PHP, I can write:

$vname = 'phone';
$$vname = '555-1234';
print $phone;

… And the script will output "555-1234".

Is there any equivalent in Perl?

Is there any way to constrain $phone to the scope of the local block, as if I'd written my $phone? Using my $$vname gives me "Can't declare scalar dereference in my at …" errors.

Best Solution

What you're attempting to do is called a "symbolic reference." While you can do this in Perl you shouldn't. Symbolic references only work with global variables -- not lexical (my) ones. There is no way to restrict their scope. Symbolic references are dangerous. For that reason they don't work under the strict pragma.

In general, whenever you think you need symbolic references you should use a hash instead:

my %hash;
$hash{phone} = '555-1234';
print $hash{phone};

There are a few cases where symrefs are useful and even necessary. For example, Perl's export mechanism uses them. These are advanced topics. By the time you're ready for them you won't need to ask how. ;-)

Related Solutions

Php – Reference — What does this symbol mean in PHP

Incrementing / Decrementing Operators

++ increment operator

-- decrement operator

Example    Name              Effect
---------------------------------------------------------------------
++$a       Pre-increment     Increments $a by one, then returns $a.
$a++       Post-increment    Returns $a, then increments $a by one.
--$a       Pre-decrement     Decrements $a by one, then returns $a.
$a--       Post-decrement    Returns $a, then decrements $a by one.

These can go before or after the variable.

If put before the variable, the increment/decrement operation is done to the variable first then the result is returned. If put after the variable, the variable is first returned, then the increment/decrement operation is done.

For example:

$apples = 10;
for ($i = 0; $i < 10; ++$i) {
    echo 'I have ' . $apples-- . " apples. I just ate one.\n";
}

Live example

In the case above ++$i is used, since it is faster. $i++ would have the same results.

Pre-increment is a little bit faster because it really increments the variable and after that 'returns' the result. Post-increment creates a special variable, copies there the value of the first variable and only after the first variable is used, replaces its value with second's.

However, you must use $apples--, since first, you want to display the current number of apples, and then you want to subtract one from it.

You can also increment letters in PHP:

$i = "a";
while ($i < "c") {
    echo $i++;
}

Once z is reached aa is next, and so on.

Note that character variables can be incremented but not decremented and even so only plain ASCII characters (a-z and A-Z) are supported.

Stack Overflow Posts:

Understanding Incrementing

PHP script to loop through all of the files in a directory

You can use the DirectoryIterator. Example from php Manual:

<?php
$dir = new DirectoryIterator(dirname(__FILE__));
foreach ($dir as $fileinfo) {
    if (!$fileinfo->isDot()) {
        var_dump($fileinfo->getFilename());
    }
}
?>

Best Solution

Related Solutions

Php – Reference — What does this symbol mean in PHP

PHP script to loop through all of the files in a directory

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