Alter a .bashrc file to enhance the shell prompt display

prompt-setup.sh

#!/bin/sh

## This Source Code Form is subject to the terms of the Mozilla Public
## License, v. 2.0. If a copy of the MPL was not distributed with this
## file, You can obtain one at https://mozilla.org/MPL/2.0/.

usage=$(cat) <<-***
Usage:  $0 BASHRCFILE

Alter a .bashrc file to enhance the shell prompt display.

  --help	display this help and exit

Locates the PS1 prompt strings in a .bashrc file, enhancing them with the
output of last exit/error status and current time, and adds PROMPT_COMMAND and
GIT_PS1_* variables, to add Git status to the prompt and configure it.
***

dieWithUsage() {
	[ "$2" ] && printf %s\\n "$2" >&2
	printf '%s\n' "$usage"
	exit "${1:-0}"
}
for arg; do
	[ "$arg" = '--help' ] && dieWithUsage
done

if [ ! -f "$1" ]; then
	dieWithUsage 1 'No BASHRCFILE specified'
fi
bashrc=$1

promptSetupComment='## The following lines have been added by the prompt-setup script.'

if grep --quiet "$promptSetupComment" "$bashrc"; then
	printf 'The file "%s" appears to have already been altered\n' "$bashrc"
	exit
fi

## Nothing should be expanding here, the '$'s are as literal as can be.
# shellcheck disable=SC2016
sed -Ei '
	## For each line that starts with PS1=<singlequote>
	/^\s+PS1='\''/{
		## Move the dollar sign suffix to a separate variable
		s/(^\s+)(\S.+)(\\\$ )('\'')$/\1\2\4\n\1PS1_suffix=\4\\n\3\4/;
		## Prefix with last exit status (if non-zero) and clock
		s/(^[^$]+)(\$)/\1$(e=$?;[ "$e" -eq 0 ]||echo "$e|")$(date +%T) \2/;
		## For each line that contains "\[" (shell prefix for ANSI escape sequences)
		/\\\[/{
			## Dim the prompt dollar sign
			s/(_.+)(\\\$)/\1\\[\\033[2m\\]\2\\[\\033[0m\\]/
			## Set color to red for error number (bright) and its separator (dim)
			s/(^.+o ")(\$e)(\|)(")/\1\\[\\033[1;31m\\]\2\\[\\033[2m\\]\3\\[\\033[0m\\]\4/;
			## Dim the clock
			s/(\$[^)]+\))( )/\\[\\033[2m\\]\1\\[\\033[0m\\]\2/;
			## Add variable to enable colors in Git prompt
			s/(^\s+)(\S.+$)/&\n\1GIT_PS1_SHOWCOLORHINTS=1/;
		}
	}' "$bashrc"

cat >>"$bashrc" <<-***

	$promptSetupComment
	GIT_PS1_SHOWDIRTYSTATE=1
	GIT_PS1_SHOWSTASHSTATE=1
	GIT_PS1_SHOWUNTRACKEDFILES=1
	GIT_PS1_SHOWUPSTREAM='verbose name'
	GIT_PS1_DESCRIBE_STYLE='branch'
	GIT_PS1_HIDE_IF_PWD_IGNORED=1

	PROMPT_COMMAND="__git_ps1 '\$PS1' '\$PS1_suffix'"
	unset PS1_suffix
	## End of content added by prompt-setup.
***