Provide way to detect whether a script is running under dsgh?

[lucaswerkmeister]

As far as I can tell, there’s no obvious and simple way for a shell script to determine whether it’s running under dgsh or an ordinary bash: $SHELL is /bin/bash, $BASH_VERSION and ${BASH_VERSINFO[@]} look just like those of a normal Bash, etc. The ways I currently know are:

• Check type call or type call_with_stdin, two default aliases of dgsh.
• Check $BASH, the full path to the shell (e. g. /usr/local/bin/dgsh). It probably contains dgsh if it’s dgsh and probably doesn’t if it’s bash.

I must admit that I didn’t notice the second way until filing this issue – I went to open it because I just knew of the first way and thougt that was too obscure. With $BASH available, I’m not sure if this issue is still necessary… do you think a dedicated variable like $DGSH should be added?

[lucaswerkmeister]

(The motivation for this issue is that it’s possible to write polyglot scripts that run under both dgsh and bash, and hide the multipipe syntax in an if is_dgsh block. The script could then offer extra features or optimizations if running under dgsh.)

[dspinellis]

Note that when running bash --dgsh the $BASH way doesn't work. One way I can think is

if {{ : ; }} ; then
  echo dgsh
else
  echo bash
fi 2>/dev/null

[lucaswerkmeister]

Why is this issue closed? Your proposed solution is alright, but without documenting it anywhere else no one will find it…

[dspinellis]

Right! I mistakenly thought that documenting it in this issue was enough. Where would you expect to find it documented? Can you please submit a corresponding pull request?

[lucaswerkmeister]

Sure, I can create a PR later.

[dspinellis]

Looking forward!

[lucaswerkmeister]

Took me a bit longer than I’d hoped for, but I’ve submitted the PR: #96.