VPK files are used in Left 4 Dead instead of GCFs, apparently something closer to NCFs. Valve has stated these have supplanted GCFs and NCFs.. The VPK.exe is a command line tool located in <Steam folder>\steamapps\common\left 4 dead\bin\vpk.exe.
A different VPK file format was originally used in Vampire the Masquerade: Bloodlines, an early Source game.
Its commands are as follows:
- vpk dirname
- Creates a pack file named <dirname>.vpk located in the parent of the specified directory.
- vpk x vpkfile filename1 filename2 ...
- Extract file(s).
- vpk a vpkfile filename1 filename2 ...
- Add file(s).
- vpk a vpkfile @filename
- Add files listed in a response file.
- vpk k vpkfile keyvalues_filename
- Add files listed in a keyvalues control file.
- vpk l vpkfile
- List contents of VPK.
- vpk L vpkfile
- List contents (detailed) of VPK.
- -v Verbose.
- -M Produce a multi-chunk pack file
Left 4 Dead and Left 4 Dead 2's vpk's are multi-chunk files. If you are looking to extract the contents of those VPK's, extract the pak01_dir.vpk. This will extract the contents of all of the vpk files.