Generate a text file with a latex formatted list

latex_list.php

<?php
header('Content-type: text/plain; charset=utf-8');

$myfile = fopen("output.txt", "w") or die("Unable to open file!");

$tasks = [
    'one task',
    'two task'
];

$content = '';
$content .= print_latex_list_format(0, "TITLE");
$content .= print_latex_list_of_list_format("TITLE", "DESCRIPTION", $tasks, "DELIVERABLE", "TIMING");



fwrite($myfile, $content);

function print_latex_list_format($number, $title)
{
    $res = "";
    $number = sprintf("%02d", $number);

    $text_bf = '\textbf';
    $res .= "\begin{itemize}\n\item ". $text_bf ."{RF-" . $number . "}: " . $title . "\n" ;
    $res .= "\begin{itemize}\n\item ". $text_bf ."{RF-". $number . ".01} Part Backend \n";
    $res .= "\item ". $text_bf ."{RF-". $number . ".02} Part Frontend \n";
    $res .= '\end{itemize}' . "\n";
    $res .= '\end{itemize}' . "\n";
    $res .= "\n\n";

    return $res;
}


function print_latex_list_of_list_format($title, $desc, $array_tasks, $deliverable, $timing)
{

    $res = "";

    $text_bf = '\textbf';
    $res .= "\begin{itemize}\n\item ". $text_bf ."{".$title."} \n" ;
    $res .= "\begin{itemize}\n\item ". $text_bf ."{Descripció: }". $desc. "\n";
    $res .= "\item ". $text_bf ."{Tasques: }\n". print_array($array_tasks) . " \n";
    $res .= "\item ". $text_bf ."{Lliurables: }". $deliverable . " \n";
    $res .= "\item ". $text_bf ."{Temps: }". $timing . " \n";
    $res .= '\end{itemize}' . "\n";
    $res .= '\end{itemize}' . "\n";
    $res .= "\n\n";

    return $res;
}

function print_array($arr)
{
    $res = "";
    $res .= "\begin{itemize}\n";
    foreach ($arr as $value) {
        $res .= "\item{" . $value . "}\n";
    }
    $res .= '\end{itemize}';
    $res .= "\n";
    return $res;
}
?>