Splitting a file with a very long comma separated string of numbers into multiple files

prog.awk

# https://stackoverflow.com/q/65964916
# Usage: awk -v limit=17577 -f prog.awk file

BEGIN {
  RS = ORS = ","
}

{
  nread++
}

nread == 1 {
  if (NR > 1) {
    printf("\n") > file
  }
  close(file)
  file = (FILENAME "_" ++nfile)
}

nread != 1 {
  print prev > file
}

nread == limit {
  printf("%s", $0) > file
  nread = 0
  next
}

{
  prev = $0
}

END {
  if (nread) {
    printf("%s", prev) > file
  }
}