Allow override of shell

[mqudsi]

hyperfine can't be used to benchmark shell-specific shell functions without launching a new instance of a shell within the shell itself, breaking some of the underlying assumptions. As most shells support the -c argument, it would useful if it were possible to pass in a --shell SHELL option to override hyperfine's default.

e.g. I'm using hyperfine to reassess some assumptions made in the development of fish shell, and would like to be able to benchmark one version of a shell builtin against another, or benchmark the time a completion script takes to execute (which uses fish-specific language so would return an error under sh).

This would be a straightforward replacement of sh with whatever the user provided, but some might even find it useful to evaluate the performance of command1 executed under shell foo and command2 executed under shell bar (and not losing the benefit of the startup timing analysis that hyperfine provides).

[sharkdp]

Thank you for the feedback. Sounds like a good idea to me!

but some might even find it useful to evaluate the performance of command1 executed under shell foo and command2 executed under shell bar (and not losing the benefit of the startup timing analysis that hyperfine provides).

That would be a little bit more complicated and would probably require different (or additional) command line options. I think it would be okay to ask users to run hyperfine multiple times (one time for each shell) in this case.

[mqudsi]

David: I had some need of this again, pull request over at #62.

[jasonpeacock]

I picked up the existing PR and updated it per the feedback & latest changes, it's available as #96.

[sharkdp]

Released in v1.4.0. Thanks everyone!