The original suggestion for an unattended install downloads the installation script to a file, then runs that file with the --unattended argument. The install.sh file would be left behind after the suggested command was run.
This change passes the --unattended argument directly into sh. So, it's a nice one-liner like the default installation script, and it doesn't leave a dangling install.sh script.

After wandering into a few articles that discuss the difference between might and may...opting for may.

Redirect stderr to avoid printing errors to the console when the ssh key is not
unlocked.

Add better usage instructions for the plugin which actually work

Just add aliases for PVC actions.

* git: add `alias grev="git revert"`

* Swapping double for single quotes

Matching the conventions in the plugin

* Clean up plugin and README
* Rename ag to age to avoid conflict with The Silver Searcher
  Fixes #3866

* Use double quotes to cache value of $apt_pref and $apt_upgr
* Clean up and fix syntax of command checks
* Clean up README and document $apt_pref/$apt_upgr overriding mechanism
* Rename `ag` alias (apt upgrade) to `au`
* Clean up README and fix syntax

Fixes #3686 
Fixes #4660 
Closes #5906
Co-authored-by: Noah Vesely <fowlslegs@riseup.net>

Zsh may be configured such that ">>" will error if the file doesn't exist (`setopt noclobber`). 

tput is error-prone and may not be needed, since all the formatting
codes used are standard across all types of terminals.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>

* gitfast: use $OSTYPE again

In the last update to upstream this was reverted:

 a56eac7a (Use OSTYPE instead of uname whenever possible for better speed. (#5496))
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>

* gitfast: simplify plugin

No need to set and unset a variable we use once.
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>

* gitfast: add script to update from upstream

This would make easier the process of updating, and also not miss our
patches.
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>

* gitfast: update to upstream v2.21
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>

installer: fix, refactor and add installer arguments

tput may throw errors on invalid $TERM values, for example.
This shorthand syntax allows for that as well as for if tput
doesn't exist.

Co-authored-by: Antonio QUINTAVALLE <antonio.quintavalle@amadeus.com>
Co-authored-by: Marc Cornellà <marc.cornella@live.com>

Co-authored-by: Liquidsoul <liquidsoul@liquidsoul.fr>
Co-authored-by: Alexander Polynomdivision <digitalmail555@googlemail.com>
Co-authored-by: loket <loket@cruftlab.io>
Co-authored-by: Connor Demille <subtlepseudonym@gmail.com>

Co-authored-by: Joel Kuzmarski <leoj3n@gmail.com>

Co-authored-by: Marshall Ford <inbox@marshallford.me>
Co-authored-by: Joel Kuzmarski <leoj3n@gmail.com>

Supposed to be POSIX-compatible. Proved to work in dash, yash and whatever
alpine uses. See https://unix.stackexchange.com/a/371873

This facilitates testing of changes to the core installation code: you'll be
able to do a roundtrip test of install and uninstall using the working code on
your branch.

Controlled by passing $REPO and $BRANCH environment variables to install.sh.