 
Use variable variables:
function eat_fruit($fruit) { print "chewing $fruit."; }
$function = 'eat_fruit';
$fruit = 'kiwi';
$function($fruit); // calls eat_fruit( )If you have multiple possibilities to call, use an associative array of function names:
$dispatch = array(
    'add'      => 'do_add',
    'commit'   => 'do_commit',
    'checkout' => 'do_checkout',
    'update'   => 'do_update'
);
$cmd = (isset($_REQUEST['command']) ? $_REQUEST['command'] : '');
if (array_key_exists($cmd, $dispatch)) {
    $function = $dispatch[$cmd];
    $function(); // call function
} else {
    error_log("Unknown command $cmd");
}This code takes the command name from a request and executes that function. Note the check to see that the command is in a list of acceptable command. This prevents your code from calling whatever function was passed in from a request, such as phpinfo( ) . This makes your code more secure and allows you to easily log errors.
Another advantage is that you can map multiple commands to the same function, so you can have a long and a short name:
$dispatch = array(
    'add'      => 'do_add',
    'commit'   => 'do_commit',   'ci' => 'do_commit', 
    'checkout' => 'do_checkout', 'co' => 'do_checkout',
    'update'   => 'do_update',   'up' => 'do_update'
);Recipe 5.5 for more on variable variables.
 
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