[chubot]

The pure bash solution has overhead too. If you need to split 1000 strings it will create, write, and read 1000 temp files. Depending on your hardware and file system, that's more expensive than creating 1000 or 2000 processes.

I would worry about making it correct before making it fast, the former being a big challenge!

Shells Use Temp Files to Implement Here Documents : http://www.oilshell.org/blog/2016/10/18.html

(Oil doesn't do this; it creates a process for here docs without touching disk. In theory this could be eliminated for here docs less than PIPE_BUF, which is probably a lot of them)

[jmcnulty]

It's the read/readarray builtin that's creating the tmpfiles and that's not great, but the string substitution doesn't. My point was there's no need to call out to another program to do something that bash is capable of doing itself.

[chubot]

No, it's the here doc, including here strings. See the blog post, which doesn't use read or readarray.

[jmcnulty]

Understand. Did some quick tests myself and see what you mean.

Here's a version that doesn't use "here string" and so doesn't create temporary files.

  #!/bin/bash

  shopt -s lastpipe

  string="Los Angeles, London, Belfast, New York"
  echo "${string/, /,}" | readarray -d, -t arrayA
  echo ${arrayA[0]}
  echo ${arrayA[1]}

Also, the lastpipe option runs the readarray in the context of the current process.