php - HTMLの特殊文字を削除する

Answer 1

Or, if you want to use a RegEx, use:

$str = 'a“bc”def°g';
$str = preg_replace("[^A-Za-z0-9 ]", "", $str);

Answer 2

One way would be (eg)

$str = 'a“bc”def°g';
$special = array('“','”','°');
$str = str_replace($special,'',$str);

Answer 3

Per the edit- to read the file contents, remove everything except alphanumerics and space characters then write the result to the same file, you can use:

$file= "yourfile.txt";
$file_content = file_get_contents($file);
$fh = fopen($file, 'w');
$file_content=preg_replace("[^A-Za-z0-9 ]", "", $file_content);
fwrite($fh, $file_content);
fclose($fh);