[Logician]

$file = strtr($file, " ", "_");

should help..

Also your both examples seem correct to me in the first look. Are you sure you didnt miss another thing? For example in your code you assigned the modified name to variable "$file1". Are you sure you use the variable "$file1" instead of $file after you replaced the chars..

As for calling your function, this is the line you should use:
$file=stripspaces($file);