Convert Dashes to CamelCase in PHP

No regex or callbacks necessary. Almost all the work can be done with ucwords:

function dashesToCamelCase($string, $capitalizeFirstCharacter = false) 
{

    $str = str_replace(' ', '', ucwords(str_replace('-', ' ', $string)));

    if (!$capitalizeFirstCharacter) {
        $str[0] = strtolower($str[0]);
    }

    return $str;
}

echo dashesToCamelCase('this-is-a-string');

If you're using PHP >= 5.3, you can use lcfirst instead of strtolower.

Update

A second parameter was added to ucwords in PHP 5.4.32/5.5.16 which means we don't need to first change the dashes to spaces (thanks to Lars Ebert and PeterM for pointing this out). Here is the updated code:

function dashesToCamelCase($string, $capitalizeFirstCharacter = false) 
{

    $str = str_replace('-', '', ucwords($string, '-'));

    if (!$capitalizeFirstCharacter) {
        $str = lcfirst($str);
    }

    return $str;
}

echo dashesToCamelCase('this-is-a-string');

This can be done very simply, by using ucwords which accepts delimiter as param:

function camelize($input, $separator = '_')
{
    return str_replace($separator, '', ucwords($input, $separator));
}

NOTE: Need php at least 5.4.32, 5.5.16

this is my variation on how to deal with it. Here I have two functions, first one camelCase turns anything into a camelCase and it wont mess if variable already contains cameCase. Second uncamelCase turns camelCase into underscore (great feature when dealing with database keys).

function camelCase($str) {
    $i = array("-","_");
    $str = preg_replace('/([a-z])([A-Z])/', "\\1 \\2", $str);
    $str = preg_replace('@[^a-zA-Z0-9\-_ ]+@', '', $str);
    $str = str_replace($i, ' ', $str);
    $str = str_replace(' ', '', ucwords(strtolower($str)));
    $str = strtolower(substr($str,0,1)).substr($str,1);
    return $str;
}
function uncamelCase($str) {
    $str = preg_replace('/([a-z])([A-Z])/', "\\1_\\2", $str);
    $str = strtolower($str);
    return $str;
}

lets test both:

$camel = camelCase("James_LIKES-camelCase");
$uncamel = uncamelCase($camel);
echo $camel." ".$uncamel;