#!/bin/bash
# sweeper.sh
# Designed around a Macbook Pro 13", OSX 10.7.5, default bash terminal.
# Issued as Public Domain, 2014, B.Walker, G0LCU.
clear
echo ""
echo "Generating the sweep.wav file, please wait a few seconds..."
echo ""
m=0
n=0
sweep_data=" ~"
sweep_text=""
# Initialise all files to zero.
> /tmp/sweeper.raw
> /tmp/sweep.raw
> /tmp/sweep.wav
# Generate the high start sound at 4KHz.
for m in $( seq 0 1 5 )
do
	printf "$sweep_data" >> /tmp/sweeper.raw
done
# Now build up the sweep_data by adding the correct byte values at the beginning first then the end last.
for n in $( seq 0 46 )
do
	# Add the correct byte at the beginning, append the file, looping a few times...
	sweep_data=' '$sweep_data
	for m in $( seq 0 1 3 )
	do
		printf "$sweep_data" >> /tmp/sweeper.raw
	done
	# Now add the correct byte at the end, append the file, looping a few times...
	sweep_data=$sweep_data'~'
	for m in $( seq 0 1 2 )
	do
		printf "$sweep_data" >> /tmp/sweeper.raw
	done
done
# Now to reverse the file sweeper.raw byte by byte using builtins and append to sweeper.raw.
# This is a little slow but it works perfectly, therefore good enough for me.
sweep_text=`cat < /tmp/sweeper.raw`
n=$[ ( ${#sweep_text} - 1 ) ]
while [ $n -ge 0 ]
do
	printf "${sweep_text:$n:1}" >> /tmp/sweeper.raw
	n=$[ ( $n - 1 ) ]
done
# Create a few seconds of sweeper from 4KHz to about 85Hz and back again...
cp /tmp/sweeper.raw /tmp/sweep.raw
cat /tmp/sweeper.raw >> /tmp/sweep.raw
# This is the required .WAV header...
printf "\x52\x49\x46\x46\x6c\xfe\x00\x00\x57\x41\x56\x45\x66\x6d\x74\x20\x10\x00\x00\x00\x01\x00\x01\x00\x40\x1f\x00\x00\x40\x1f\x00\x00\x01\x00\x08\x00\x64\x61\x74\x61\x48\xfe\x00\x00" >> /tmp/sweep.wav
cat /tmp/sweep.raw >> /tmp/sweep.wav
echo "All done, now sweeping from 4KHz to about 85 Hz and back..."
echo "Press Ctrl-C to stop..."
while true
do
	# For Linux use aplay in place of afplay.
	afplay /tmp/sweep.wav
done
# The line below will never be reached but added for fullness...
exit 0