Split and combine files in Linux

Assume myfile is a 160KB file:

split -b 40k myfile segment

This will output four 40KB files: segmentaa, segmentab, segmentac, and segmentad

Assume myfile is 3000 lines long:

split -l 500 myfile segment

This will output six 500-line files: segmentaa, segmentab, segmentac, segmentad, segmentae, and segmentaf

You can combine them with cat command

You may also wish to investigate the csplit command