Question

I’ve got a large (by number of lines) plain text file that I’d like to split into smaller files, also by number of lines. So if my file has around 2M lines, I’d like to split it up into 10 files that contain 200k lines, or 100 files that contain 20k lines (plus one file with the remainder; being evenly divisible doesn’t matter).

I could do this fairly easily in Python, but I’m wondering if there’s any kind of ninja way to do this using Bash and Unix utilities (as opposed to manually looping and counting / partitioning lines).

Answer 1

Have a look at the split command:

$ split --help
Usage: split [OPTION] [INPUT [PREFIX]]
Output fixed-size pieces of INPUT to PREFIXaa, PREFIXab, ...; default
size is 1000 lines, and default PREFIX is `x'.  With no INPUT, or when INPUT
is -, read standard input.

Mandatory arguments to long options are mandatory for short options too.
  -a, --suffix-length=N   use suffixes of length N (default 2)
  -b, --bytes=SIZE        put SIZE bytes per output file
  -C, --line-bytes=SIZE   put at most SIZE bytes of lines per output file
  -d, --numeric-suffixes  use numeric suffixes instead of alphabetic
  -l, --lines=NUMBER      put NUMBER lines per output file
      --verbose           print a diagnostic to standard error just
                            before each output file is opened
      --help     display this help and exit
      --version  output version information and exit

You could do something like this:

split -l 200000 filename

which will create files each with 200000 lines named xaa xab xac …

Another option, split by size of output file (still splits on line breaks):

 split -C 20m --numeric-suffixes input_filename output_prefix

creates files like output_prefix01 output_prefix02 output_prefix03 ... each of maximum size 20 megabytes.