- array_map: documentation ( source)
<?php
//First, use file() to get array of lines from your text file, then...
$array_from_file = array('String1', 'String2', 'String3');
$array_from_file = array_map(function($x){return $x = '"'.$x.'"';}, $array_from_file);
foreach ($array_from_file as $line) {
echo $line . "\n";
}