rot135

#!/usr/bin/env bash
#######################################################################
# Made by    : Ewoud Dronkert
# Licence    : GNU GPL v3
# Platform   : BSD/Linux
# Requires   : bash, POSIX, file, tr
# Location   : ~/bin, /usr/local/bin
# Name       : rot135
# Version    : 1.0.2
# Date       : 2018-08-14
# Purpose    : Encode or decode any (US-ASCII) text using ROT13 and
#              numbers using ROT5. You will never break this cypher!!1
# Parameters : Text to be encoded, or a text file name.
# Input      : Original text via a pipe, or as parameter(s).
# Output     : Translated text on stdout. Error message on stderr.
# Settings   : none
# Exit     0 : No error
#          1 : No input detected
#######################################################################

function tr_rot135() {
	tr a-zA-Z0-9 n-za-mN-ZA-M5-90-4
}

if [ ! -t 0 ]; then
	# Piped input, probably
	tr_rot135
	exit 0
fi

if [ -z "$1" ]; then
	# No input detected
	self=$(basename "$0")
	echo "Usage 1: $self <text>" 1>&2
	echo "Usage 2: $self <filename.txt>" 1>&2
	echo "Usage 3: echo <text> | $self" 1>&2
	exit 1
fi

if [ "$#" -eq 1 -a -f "$1" -a -r "$1" ]; then
	# Single argument is a file that can be read
	mime=$(file -b -i -eencoding "$1" | cut -d';' -f1)
	if [ "$mime" = "text/plain" ]; then
		# It is a text file (encoding not checked)
		cat "$1" | tr_rot135
		exit 0
	fi
fi

# Use argument(s) as text
echo "$*" | tr_rot135