Here are two PHP functions to convert strings between underscore format and camel case

camel_case_functions.php

<?php
/**
 * Translates a camel case string into a string with
 * underscores (e.g. firstName -> first_name)
 *
 * @param string $str String in camel case format
 * @return string $str Translated into underscore format
 */
function fromCamelCase($str) {
  $str[0] = strtolower($str[0]);
  $func = create_function('$c', 'return "_" . strtolower($c[1]);');
  return preg_replace_callback('/([A-Z])/', $func, $str);
}

/**
 * Translates a string with underscores
 * into camel case (e.g. first_name -> firstName)
 *
 * @param string $str String in underscore format
 * @param bool $capitaliseFirstChar If true, capitalise the first char in $str
 * @return string $str translated into camel caps
 */
function toCamelCase($str, $capitaliseFirstChar = false) {
  if($capitaliseFirstChar) {
    $str[0] = strtoupper($str[0]);
  }
  $func = function($c){ return strtoupper($c[1]);};
  return preg_replace_callback('/_([a-z])/', $func, $str);
}
?>