Results, lines in receiving files:
 Expecting first lines, 1(20), 21(10), 31(10), 51(10), 61-100
 Note - accepting partial completion on r05, exit.
Edges: 1:0:0 of 20 lines in file "r01"
f1
   ---

Edges: 1:0:0 of 10 lines in file "r02"
f21
   ---

Edges: 1:0:0 of 10 lines in file "r03"
f31
   ---

Edges: 1:0:0 of 10 lines in file "r04"
f51
   ---

Edges: 1:0:0 of 40 lines in file "r05"
f61
   ---

r3split -c "20,10+2,-10,10," -p "r" $FILE

r3split - Split text file into Ratio, iRregular, or Random chunks.

usage: r3split [options] -- [files]

options:

Options which allow arguments require either a space or an "=" as
a separator, e.g. "-r 3" or "-r=3".

--help | -h
  print this message and quit.

--chunks | -c [-]c1,[-]c2 ... cn
  Transfer ci lines to next output file.  If preceded by "-" skip
  ci lines.  For convenience, the ci sequence may be the first
  parameter (or second after the --debug option).

  The chunks may be integers, ratios ( 1 < ci < 0 ), percentages
  (similar to ratios but 100 < ci < 0, followed by "%")  Ratios
  and percentages will require a preliminary (fast) pass over the
  file to find the length in lines (see "estimate:).  A count of
  zero will be treated as 1.

  If the symbol "+" occurs after the chunk, an integer repeat
  count may be specified.

  Usually the chunks are transferred in complete blocks, and
  remaining lines less than a chunk are ignored.  However if a
  final comma, ",", appears, then the incomplete chunk will be
  transferred to the final file. (Essentially a large number is
  created for the final chunk.)

  Ex: -c=1,1    --chunks 20%,.3,100     --chunks=-4,13,.75
  -c 3,3+       -c3,3+,

--random | -r n
  Transfer to n files, each file containing a random number of
  lines.  The total lines will equal the number of lines in the
  input file.  The NUMBER of lines is random here, the sequence
  is as it appears in the input.

--debug | -d
  Print debugging output.  Must be first option.
  
--suffix | -s format
  Suffix format, the default is "%02d".  To specify a ".txt" for
  each file use -s="%02d.txt".  The format is used to create the
  sequence of output filenames.

--prefix -p string
  Prefix, default is "xx", like many other split utilities.

--estimate | -e
  Allow the file length to be estimated, generally useful only
  for "long" files, perhaps 1 GB or more.  (This is accomplished
  by external routine "esmele" which might not be available on
  all systems.)