<?php
$o = array(1,2,3,4,5);
$ha =fopen("1.txt", 'a');
foreach($o as $z)
{ $znacheniya .="$z".';'; }
fwrite ($ha,"$znacheniya");
fclose($ha);
?>

Емае
$fo = fopen('file','a;
foreach($array as $val){
fwrite($fo,$val."\n");
}
fclose($fo);