> I have yet to encounter a system where bash wasn't available, so yes I'd say it's quite portable.
Most systems (other than linux and OS X) do not include bash by default, and not everyone is able or willing to install it (and its dependencies) just to run a silly shell script. Sh one the other hand is almost as universal as ed(1), and implements the most sane subset of bash anyway.
Other systems (eg., Plan 9) don't have bash available at all (this is considered by some as a feature), while bourne is supported, if only for backwards compatibility.
> In my opinion all shells are quite horrible.
Most mainstream shells are indeed horrible (don't get me started on csh), but [there are some quite sane shells out there](http://rc.cat-v.org).
> The idea is to pick the lowest common denominator and bash just happens to be the most popular of the bunch.
lowest common denominator != most popular of the bunch.
> Your chances of finding a working /bin/bash on any given system are still orders of magnitude higher than finding a working capistrano/fabric along with the corresponding ruby/python toolchain.
And your chances of finding a working /bin/sh on any given system are still orders of magnitude higher than finding a working /bin/bash
Most systems (other than linux and OS X) do not include bash by default, and not everyone is able or willing to install it (and its dependencies) just to run a silly shell script. Sh one the other hand is almost as universal as ed(1), and implements the most sane subset of bash anyway.
Other systems (eg., Plan 9) don't have bash available at all (this is considered by some as a feature), while bourne is supported, if only for backwards compatibility.
> In my opinion all shells are quite horrible.
Most mainstream shells are indeed horrible (don't get me started on csh), but [there are some quite sane shells out there](http://rc.cat-v.org).
> The idea is to pick the lowest common denominator and bash just happens to be the most popular of the bunch.
lowest common denominator != most popular of the bunch.
> Your chances of finding a working /bin/bash on any given system are still orders of magnitude higher than finding a working capistrano/fabric along with the corresponding ruby/python toolchain.
And your chances of finding a working /bin/sh on any given system are still orders of magnitude higher than finding a working /bin/bash