If you mean an equal number of lines, split has an option for this:
split --lines=75
If you need to know what that 75 should really be for N equal parts, its:
lines_per_part = int(total_lines + N - 1) / N
where total lines can be obtained with wc -l.
See the following script for an example:
#!/usr/bin/bash
# Configuration stuff
fspec=qq.c
num_files=6
# Work out lines per file.
total_lines=$(wc -l <${fspec})
((lines_per_file = (total_lines + num_files - 1) / num_files))
# Split the actual file, maintaining lines.
split --lines=${lines_per_file} ${fspec} xyzzy.
# Debug information
echo "Total lines = ${total_lines}"
echo "Lines per file = ${lines_per_file}"
wc -l xyzzy.*
This outputs:
Total lines = 70
Lines per file = 12
12 xyzzy.aa
12 xyzzy.ab
12 xyzzy.ac
12 xyzzy.ad
12 xyzzy.ae
10 xyzzy.af
70 total
More recent versions of split allow you to specify a number of CHUNKS with the -n/--number option. You can therefore use something like:
split --number=l/6 ${fspec} xyzzy.
(that's ell-slash-six, meaning lines, not one-slash-six).
That will give you roughly equal files in terms of size, with no mid-line splits.
I mention that last point because it doesn't give you roughly the same number of lines in each file, more the same number of characters.
So, if you have one 20-character line and 19 1-character lines (twenty lines in total) and split to five files, you most likely won't get four lines in every file.