opendir
See the current Perl documentation for opendir.
Here is our local, out-dated (pre-5.6) version:
opendir - open a directory
opendir DIRHANDLE,EXPR
Opens a directory named EXPR for processing by readdir(), telldir(), seekdir(), rewinddir(), and closedir(). Returns TRUE if successful. DIRHANDLEs have their own namespace separate from FILEHANDLEs.