PHP is my function called from echo, or sprintf

Question

I want to look where the function is called.

Is the function called inside a echo or sprintf? Then return, otherwise echo the content.

I got this code (test.php):

<?php
function __($str = '')
{
    // who is my parent?
    $parent=debug_backtrace();

    if ( isset ( $parent[1] ) )
        $parent = $parent[1]['function']; //Did it!
    else
        $parent = debug_backtrace()[1]['function']; //Try

    if ( empty ( $parent ) )
        $parent = "ERROR!";

    return sprintf("[%s] %s.%s", $parent, $str, PHP_EOL);
}

__('does nothing');
echo __('test from echo #1');
echo(__('test from echo #2'));
echo sprintf(__('test from sprintf #1'));
echo(sprintf(__('test from sprintf #2')));
?>

When I type it at the terminal all I get is:

WDGMBP:Test Wes$ php test.php 
[ERROR!] test from echo #1.
[ERROR!] test from echo #2.
[ERROR!] test from sprintf #1.
[ERROR!] test from sprintf #2.

(p.s. from web the same)

My PHP version is:

WDGMBP:BIHappyV3 Wes$ php -v
PHP 5.5.27 (cli) (built: Aug 22 2015 18:20:44) 
Copyright (c) 1997-2015 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2015 Zend Technologies

Answer 1

You're confused about how debug_backtrace works. It returns the functions that were executing to make the call, not the function that will be called with the result. E.g. if you have:

function testit() {
    someFunc(__('something'));
}

then $parent[1]['function'] will contain testit, not someFunc.

I don't think there's any way to get someFunc. That function isn't anywhere on the stack, because it doesn't get called until after __() returns.