您可以使用
fopen和
fseek
define('SIZE',100); // size of the file to be created.
$fp = fopen('somefile.txt','w'); // open in write mode.
fseek($fp,SIZE-1,SEEK_CUR); // seek to SIZE-1
fwrite($fp,'a'); // write a dummy char at SIZE position
fclose($fp); // close the file.
执行时：
$PHP a.PHP $wc somefile.txt 0 1 100 somefile.txt $
