PHP file operation to a file to write data

//Open a file$f=fopen($filename, ' WB ');$filename:opening a file that does not exist is automatically created if it cannot be created, stating that the specified file directory has the wrong WB:how to write----overwrite the original content
AB: Append method----Append data to the end of the fileif(!$f) {     die("Open file Failed"); } Else {    Echo' Open file succeeded '. " <br/> ";}
//determine if the file is writableif(!is_writable($f)) {     die("This file is not writable");} Else {    //echo "The file can be written"; Write data to this resource    if(!fwrite($f,$data)) {           die(' Write Failed '); } Else {          Echo"Write succeeded"; }}//Close Resourcefclose($f);

PHP file operation to a file to write data