https://twitter.com/IQAndreas/status/869975003135180801

filename.sh

#!/bin/bash

# --------------------------------------------------------------------------- #
# Created by Andreas Renberg (https://github.com/IQAndreas)
# Based on work by Doctor J (https://stackoverflow.com/a/1403489/617937)
# This code is in the public domain and under no license.
# Well, my code at least. The ~8 lines by Doctor J still belong to him.
# --------------------------------------------------------------------------- #

# Personal notes: What if a file is named 'file.'?
# Right now, it gives basename='file.' ext=''
# But I really don't know a "right" way of doing this behavior.
# This is fine.

FULL_PATH=;

print_value='%f'; # Default
extended=;

for arg in "$@"
do
    case "$arg" in
    
    # You can set these arguments more than once. Only the last one is used.
	--dir)       print_value='%d';;  # (/path/file.tar.gz -> /path/)
	--filename)  print_value='%f';;  # (/path/file.tar.gz -> file.tar.gz)
	--basename)  print_value='%b';;  # (/path/file.tar.gz -> file.tar)
	--ext)       print_value='%e';;  # (/path/file.tar.gz -> gz)
	--extension) print_value='%e';;  # (/path/file.tar.gz -> gz)  # Alternative to --ext
	
	# Extended extensions means the file 'file.tar.gz' has the extension 'tar.gz'
	--extended)  extended=true;;  # (/path/file.tar.gz -> tar.gz)
	
	--*)
		>&2 echo "Unknown argument '$arg'";
		exit 1;
		;;
		
	*)
		if [[ -z "$FULL_PATH" ]]; then
			FULL_PATH="$arg";
		else
			>&2 echo "Too many file names provided";
			exit 1;
		fi
		;;
		
	esac
	
	#DISABLED
	#	--basename-extended) print_value='%B';; # (/path/file.tar.gz -> file)  # Actually, this means extended extensions 
	#	--ext-extended) print_value='%E';;      # (/path/file.tar.gz -> file)  # Actually, this means extended extensions 
done


# Thank you, Doctor J
# https://stackoverflow.com/a/1403489/617937

filename="${FULL_PATH##*/}"                       # Strip longest match of */ from start
dir="${FULL_PATH:0:${#FULL_PATH} - ${#filename}}" # Substring from 0 thru pos of filename

if [[ -n "$extended" ]]; then
	base="${filename%%.[^.]*}";      # Strip longest match of . plus at least one non-dot char from end
	ext="${filename:${#base} + 1}";  # Substring from len of base thru end
else
	base="${filename%.[^.]*}";       # Strip shortest match of . plus at least one non-dot char from end
	ext="${filename:${#base} + 1}";  # Substring from len of base thru end
fi

# If we have an extension and no base, it's really the base
if [[ -z "$base" && -n "$ext" ]]; then
    base=".$ext"
    ext=""
fi


# This will eventually be replaced by a "date +format" type deal
case "$print_value" in
	%d) echo "$dir";;
	%f) echo "$filename";;
	%b) echo "$base";;
	%e) echo "$ext";;

	*)
		>&2 echo "NOTE TO DEVELOPER: You done fudged up. I have no idea what the flag '$print_value' is supposed to represent.";
		exit 1;
		;;
	
esac