sortable split output files

[ggrothendieck]

When using gocsvs split the output file names have suffix such as -1.csv, etc. so if there are more than 9 the filenames don't sort properly. Would be nice to be able to optionally zero pad the number in the suffix with sufficient zeroes that they sort properly.

[zacharysyoung]

split streams the output, swapping to a new output CSV as soon as the current CSV fills up to max-rows; split cannot know ahead of time how many files will be created, and so cannot calculate the padding.

That said, it can write the outputs to temp files, keeping track of the file count, then do a final rename with the correct padding. This would have the downside that if you were looking in some file explorer or watching/ls'ing you wouldn't see any incremental progress.

[zacharysyoung]

I made a little command-line tool that can fix this after running split, by giving it the prefix for the split CSVs: https://github.com/zacharysyoung/gocsv-padsplits.