split -bbytes inputfile prefix
creates files prefixaa,prefixab, all of size bytes until all
possible [a-z][a-z] are exausted. ( or end of file)
add -d to make it use 00, 01, 02..
and -a3 to 3 digit numbers.
for mastersplitter style use:
split -b1000000 -a3 -d inputfile multipart.
except, in this form the .000 file has content.
The file can be re-joined by cat multipart.* > combined_file
This isn't really part of bash (or any other shell) it's actualy a program in /usr/bin.
split command linux example