how to edit text?helphelphelp!!!

[Anon]

my subject are:
1.to get an appointed line from a text file, and change some characters of its, not all, then put it back ,just the origenal line.

2.to add a new line just behind the appointed line

[mrskhris]

http://www.php.net/manual/en/function.fopen.php

http://www.php.net/manual/en/function.file.php

http://www.php.net/manual/en/function.fwrite.php

http://www.php.net/manual/en/function.fclose.php