/bin/bash is on literally every machine I ever touch. It is on every Debian machine. It is on every Ubuntu machine. It is on every OS X machine. It is on every Windows (!) machine. And there are plenty of operations that are significantly more cumbersome to write in Ruby--otherwise, sure, I would do so. Backticks are nice, but there's no `set -e` (that I am aware of) and it becomes a huge hassle to do things in a smart, error-checking way.
No-one claimed Bash isn't widely distributed and installed by default.
However, unless you are patching and compiling the same version of Bash, you absolutely do not have the same version on all those machines, and that is the whole reason NOT to target Bash in shell scripts - its features are not always consistent/compatible across versions.
> /bin/bash is on literally every machine I ever touch. It is on every Debian machine. It is on every Ubuntu machine. It is on every OS X machine. It is on every Windows (!) machine.
Yes. Yes. Yes. Yes. No (unless Cygwin is installed).
Writing to '/bin/sh' is understandable due to its ubiquitousness.
Bash is a superset that is not so ubiquitous, so it doesn't have the advantage that writing to /bin/sh does.
If you don't want portable, then don't write to shell script. Write to Perl Ruby or Python, which is also safer and more secure.