Split large file into smaller ones:
Coreutils.
split file my/prefix
d: use numeric suffixes:
prefix00
prefix01
prefix02
instead of the default a, b, c...
Bytes per file:
split -n1M file.txt
Maximum size per file, and only whole lines are split:
split -C1M file.txt
Control number of prefix bytes.
If you generate more files than the prefix length, you need this, or else different prefix lengths are used.
E.g.:
00/00/00
00/00/01
...
99/99/99