How to trim each line in a heredoc (long string) in PHP

function trimHereDoc($t)
{
    return implode("\n", array_map('trim', explode("\n", $t)));
}

Simple solution

<?php
$txtArray = explode("\n", $txt);
$txtArray = array_map('trim', $txtArray);
$txt = implode("\n", $txtArray);

function trimHereDoc($txt)
{
    return preg_replace('/^\s+|\s+$/m', '', $txt);
}

^\s+ matches whitespace at the start of a line and \s+$ matches whitespace at the end of a line. The m flag says to do multi-line replacement so ^ and $ will match on any line of a multi-line string.

function trimHereDoc($txt)
{
    return preg_replace('/^\h+|\h+$/m', '', $txt);
}

While \s+ removes empty lines, keeps \h+ each empty lines