How to convert PascalCase to pascal_case?

Question

If I had:

$string = \"PascalCase\";

I need

\"pascal_case\"

Does PHP offer a function for this purpose?

Answer 1

The direct port from rails (minus their special handling for :: or acronyms) would be

function underscore($word){
    $word = preg_replace('#([A-Z\d]+)([A-Z][a-z])#','\1_\2', $word);
    $word = preg_replace('#([a-z\d])([A-Z])#', '\1_\2', $word);
    return strtolower(strtr($word, '-', '_'));
}

Knowing PHP, this will be faster than the manual parsing that's happening in other answers given here. The disadvantage is that you don't get to chose what to use as a separator between words, but that wasn't part of the question.

Also check the relevant rails source code

Note that this is intended for use with ASCII identifiers. If you need to do this with characters outside of the ASCII range, use the '/u' modifier for preg_matchand use mb_strtolower.

Answer 2

A concise solution and can handle some tricky use cases:

function decamelize($string) {
    return strtolower(preg_replace(['/([a-z\d])([A-Z])/', '/([^_])([A-Z][a-z])/'], '$1_$2', $string));
}

Can handle all these cases:

simpleTest => simple_test
easy => easy
HTML => html
simpleXML => simple_xml
PDFLoad => pdf_load
startMIDDLELast => start_middle_last
AString => a_string
Some4Numbers234 => some4_numbers234
TEST123String => test123_string
hello_world => hello_world
hello__world => hello__world
_hello_world_ => _hello_world_
hello_World => hello_world
HelloWorld => hello_world
helloWorldFoo => hello_world_foo
hello-world => hello-world
myHTMLFiLe => my_html_fi_le
aBaBaB => a_ba_ba_b
BaBaBa => ba_ba_ba
libC => lib_c

You can test this function here: http://syframework.alwaysdata.net/decamelize

Answer 3

Here is my contribution to a six-year-old question with god knows how many answers...

It will convert all words in the provided string that are in camelcase to snakecase. For example "SuperSpecialAwesome and also FizBuzz καιΚάτιΑκόμα" will be converted to "super_special_awesome and also fizz_buzz και_κάτι_ακόμα".

mb_strtolower(
    preg_replace_callback(
        '/(?<!\b|_)\p{Lu}/u',
        function ($a) {
            return "_$a[0]";
        },
        'SuperSpecialAwesome'
    )
);

Answer 4

Yii2 have the different function to make the word snake_case from CamelCase.

    /**
     * Converts any "CamelCased" into an "underscored_word".
     * @param string $words the word(s) to underscore
     * @return string
     */
    public static function underscore($words)
    {
        return strtolower(preg_replace('/(?<=\\w)([A-Z])/', '_\\1', $words));
    }

Answer 5

Short solution:

$subject = "PascalCase";
echo strtolower(preg_replace('/\B([A-Z])/', '_$1', $subject));

Answer 6

The worst answer on here was so close to being the best(use a framework). NO DON'T, just take a look at the source code. seeing what a well established framework uses would be a far more reliable approach(tried and tested). The Zend framework has some word filters which fit your needs. Source.

here is a couple of methods I adapted from the source.

function CamelCaseToSeparator($value,$separator = ' ')
{
    if (!is_scalar($value) && !is_array($value)) {
        return $value;
    }
    if (defined('PREG_BAD_UTF8_OFFSET_ERROR') && preg_match('/\pL/u', 'a') == 1) {
        $pattern     = ['#(?<=(?:\p{Lu}))(\p{Lu}\p{Ll})#', '#(?<=(?:\p{Ll}|\p{Nd}))(\p{Lu})#'];
        $replacement = [$separator . '\1', $separator . '\1'];
    } else {
        $pattern     = ['#(?<=(?:[A-Z]))([A-Z]+)([A-Z][a-z])#', '#(?<=(?:[a-z0-9]))([A-Z])#'];
        $replacement = ['\1' . $separator . '\2', $separator . '\1'];
    }
    return preg_replace($pattern, $replacement, $value);
}
function CamelCaseToUnderscore($value){
    return CamelCaseToSeparator($value,'_');
}
function CamelCaseToDash($value){
    return CamelCaseToSeparator($value,'-');
}
$string = CamelCaseToUnderscore("CamelCase");