How to find and delete files older than specific days in unix?

You could start by saying find /var/dtpdev/tmp/ -type f -mtime +15. This will find all files older than 15 days and print their names. Optionally, you can specify -print at the end of the command, but that is the default action. It is advisable to run the above command first, to see what files are selected.

After you verify that the find command is listing the files that you want to delete (and no others), you can add an "action" to delete the files. The typical actions to do this are:

1. -exec rm -f {} \; (or, equivalently, -exec rm -f {} ';')
   This will run rm -f on each file; e.g.,

   rm -f /var/dtpdev/tmp/A1/B1; rm -f /var/dtpdev/tmp/A1/B2; rm -f /var/dtpdev/tmp/A1/B3; …
   

2. -exec rm -f {} +
   This will run rm -f on many files at once; e.g.,

   rm -f /var/dtpdev/tmp/A1/B1 /var/dtpdev/tmp/A1/B2 /var/dtpdev/tmp/A1/B3 …
   

   so it may be slightly faster than option 1.  (It may need to run rm -f a few times if you have thousands of files.)

3. -delete
   This tells find itself to delete the files, without running rm. This may be infinitesimally faster than the -exec variants, but it will not work on all systems.

So, if you use option 2, the whole command would be:

find /var/dtpdev/tmp/ -type f -mtime +15 -exec rm -f {} +