Decide whether to support cmd.exe or not

[rdsubhas]

cmd.exe support was recently contributed, thanks to @blaubaer. But we are discovering that there is more specifics involved:

• Subshells ($(command ...))
• Variable substitution ($VAR, ${VAR}, ${VAR:-default}, etc)
• Environment variable cascading to further subcommands
• Exit codes
• Piping (foo | grep), Tests (&&, ||), I/O Redirection (>, >>)
• Any other sh "standard" expectations that we miss?
• cmd.exe vs powershell

Keeping this issue open and 1.0.0 release on hold until this is decided.

[blaubaer]

Using of UNIX features within myke config files is not a good idea in case of cross platform compatibility. The Windows shell works simply completely different and use different syntax.

• Subshells ($(command ...))

Windows similar variant (nut not equal):
for /f "tokens=*" %%i in ('command ...') do set VAR=%%i

• Variable substitution ($VAR, ${VAR}, ${VAR:-default}, etc)

Generally the CMD of windows uses %VAR% instead of $VAR or ${VAR}.

Environment variable cascading to further subcommands
Exit codes
Piping (foo | grep), Tests (&&, ||), I/O Redirection (>, >>)

This works similar. Could only be that this does not work 100% well we need tests that shows the expected and currently failing behavior.

Generally I propose the following:

1. Remove the Golang Variable expansion from the code for Windows.
2. Added all system stable variant to execute things like subshells, variables ({{.var}}), piping etc.
3. Add a general warning if someone uses System specific commands or operations like $VAR, subshells etc.

...because the target should be to have a platform and system specific independent tool. Also specific differences in *nix system can lead to poor user experience in using such tool.

[rdsubhas]

Yep @blaubaer it already takes a certain amount of knowledge to make a script work with both /bin/sh and /bin/bash, for example. So writing scripts that work in windows/linux is pretty much a big scope. Hence, I'd like to propose the following:

• Already all CLI task aggregation tools (make, robo, etc linked on the README) have standardized around /bin/sh, which is cross platform

• For v1.0.0, its may not be good to take such a big step forward, as it may postpone indefinitely

• Let's standardize on /bin/sh as a minimum requirement, because end of the day, myke is primarily a script entrypoint/aggregator (makefile equivalent) and it doesn't actually do anything other than invoking tasks

• For the next 1.1 release, we can add platform-specific commands for tasks. i.e.

  task:
    cmd:
      {{ if eq .platform windows }} windows commands {{ end }}
      {{ if eq .platform linux }} linux commands {{ end }}
  

We'll definitely get the semantics better (this is not a suggestion), but you get the overall gist :) This can be solved with templating, rather than trying to parse scripts and warn people on differences between /bin/sh, /bin/bash and cmd.exe, which will be a HUGE work of going through all these shell standards, and writing parsers for that.

[rdsubhas]

Closing to release v1.0.0. /bin/sh is the default shell used across platforms. Supporting multiple shells is right now possible with a shell: argument in tasks, broad multi-shell compatibility across scripts is out of scope of myke - its the developer (or) script writer's call, and whether to support cmd.exe or powershell, and in general multi-shell support, is moved to a different issue.