I installed pure-ftpd by RPM on my CentOS 5 test system, I was able to login as a anonymous user however I was not able to login as the standard unix user as which are defined in /etc/passwd.
I was not using the pureftpd virtual users and was running Pure-Ftpd directly from command line without the use of the configuration file.

I had run the pure-ftpd daemon by simply issuing the pure-ftpd command in shell, anyway after struggling a bit and looking here and there I found out that If you want to user simple Unix Authentication with Pure-FTPD than you will have to run it with the -l unix switch

pure-ftpd -l unix

if you want to Search for a particular string or text and replace it with a new value in files in Sub directories of a folder than it can be easily achieved using sed , you do not need to use any lengthy script to perform this simple search and replace task in a folder and all its child directories

simply use change to that directory and issue the following command, of-course change the replacement text according to your needs

.
.
.
.
find ./ -type f -exec sed -i 's/toreplace/replacedtext/g' {} \;