For example, to split the file enorme.bib in different parts each one 10000 bytes sized and named partaa, partab, partac, ..., you can launch this command
Then to simply join the files in enormereborn.bib you can use:
For more information about this commands typ:
in a terminal.
2) If you don't want to use command and terminal but you like graphical approaches, you can use HJSplit downloadable here. After you downloaded and extracted hjsplitlx.tar.gz you can enter the folder hjsplitlx and simply double click on hjsplit, so you will have a very easy interface to join/split everything.
3) Alternatively you can use FFSJ downloadable here only as EXE for Windows. So after the download of FFSJ.exe you can use wine to execute it (look here about how to install and use wine), simply launching:
4) If you downloaded some files name like bigFile.001, bigFile.002, etc., you can also join them by simply using a compressing tool like that one preinstalled in Ubuntu systems, right clicking on the first file bigFile.001 and then chosing Extract here. Then the program will make the join automatically looking for other parts in the same folder.