What is the PHP shorthand for: print var if var exist

For PHP >= 7.0:

As of PHP 7 you can use the null-coalesce operator:

$user = $_GET['user'] ?? 'guest';

Or in your usage:

<?= $myVar ?? '' ?>

For PHP >= 5.x:

My recommendation would be to create a issetor function:

function issetor(&$var, $default = null) {
    return isset($var) ? $var : $default;
}

This takes a variable as argument and returns it, if it exists, or a default value, if it doesn't. Now you can do:

echo issetor($myVar);

But also use it in other cases:

$user = issetor($_GET['user'], 'guest');

Another option:

<input value="<?php echo isset($var) ? $var : '' ?>">