POSIX shell compliance

[r2evans]

Remove bashisms so it can be run in a posix-shell environment. The impetus for this is running pushbullet-bash on a DD-WRT (customizable wireless router) instance with /bin/sh only, bash is often not installed.

[fbartels]

Hi @r2evans,

I've adopted your changes a bit and pushed the current code to https://github.com/Red5d/pushbullet-bash/tree/r2evans-posixShell. So far the changes look good and it would be ok to merge from my side.

@Red5d since this diverts a bit from "This is intended to be a pure Bash utility with no non-Bash dependencies." to posix compatibility I did not want to merge it right away. Are you ok with the merge?

[r2evans]

@fbartels @Red5d

I updated the branch to reflect the merge of errorCodes, and this includes a change to README.

[fbartels]

Looks good to me. The case can also be changed after merge imho.

if no objections from @Red5d I would merge at the end of the week.

[fbartels]

while this is a correct translation of the code, I think this is not that the original intention was. I think instead this should be

case ...
*"The param 'channel_tag' has an invalid value."* | *"The param 'device_iden' has an invalid value."*)
...

[Red5d]

Merged. While it is a slight departure from being "pure Bash", it fits the intent of not requiring additional dependencies and can be run "as is".