php is_writable function introduction

is_writable — Determine whether the given file name is writable. The result of this function will be cached. Please use clearstatcache() to clear the cache.

Syntax:

bool is_writable (string $filename)

Returns TRUE if the file exists and is writable. The filename parameter can be a directory name that allows writability checking.

Remember that PHP may only be able to access files under the username running the webserver (usually 'nobody'). Does not count towards Safe Mode limits.

Parameters:

filename The name of the file to be checked.

Return value:

Returns TRUE if the file filename exists and is writable.

php is_writable instance

Use the is_writable function to determine whether a given file is readable:

<?php
$filename = "test.text";
if (is_readable($filename)) {
  echo "文件 $filename 可读";
} else {
  echo "文件 $filename 不可读";
}
?>

In fact, we can also write a function ourselves to determine whether the file is readable, and There is no need to use PHP's built-in function is_writable. The following functions can be used to replace PHP's built-in is_writable function. You can refer to it:

//可用于替换php内置的is_writable函数
function isWritable($filename){
  if(preg_match('/\/$/',$filename)){
    $tmp_file=sprintf('%s%s.tmp',$filename,uniqid(mt_rand()));
    return isWritable($tmp_file);
  }
  if(file_exists($filename)){
    //文件已经存在的话，使用读写方式打开
    $fp=@fopen($filename,'r+');
    if($fp){
      fclose($fp);
      return true;
    }
    else{
      return false;
    }
  }
  else{
    $fp=@fopen($filename,'w');
    if($fp){
      fclose($fp);
      unlink($filename);
      return true;
    }
    else{
      return false;
    }
  }
}

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