UNIX for Dummies Questions & Answers

#!/bin/bash

# Set the startup values...
data="?"
freq=0
number=""
subscript=0
waveform=0

# An initial screen...
clear
printf "\nA simple 50 Hz to 3500 Hz audio frequency counter.\n"
printf "(C)2013, B.Walker, G0LCU. Issued as Public Domain.\n"
printf "Accuracy is within 0.1 percent of the displayed frequency...\n"
printf "\nFrequency is "$freq"Hz...\n\n"

while true
do
	# This is a demo mode so that there is no need to access HW.
	> /tmp/sinewave.raw
	# This is the binary byte data list for the crude sinewave.
	data="\\x80\\x26\\x00\\x26\\x7F\\xD9\\xFF\\xD9"
	# Generate an 8000 byte file...
	for waveform in {0..999}
	do
	        printf "$data" >> /tmp/sinewave.raw
	done
	# These two modes are for various *NIX flavours using the sound sources as required.
	# dd if=/dev/dsp of=/tmp/sinewave.raw bs=8000 count=1
	# /Users/barrywalker/Downloads/sox-14.4.0/sox -q -V0 -d -t raw -r 8000 -b 8 -c 1 -e unsigned-integer -> /tmp/sinewave.raw trim 0 00:01
	subscript=0
	freq=0
	number=`hexdump -n1 -s$subscript -v -e '1/1 "%u"' /tmp/sinewave.raw`
	while true
	do
		# Assume a square wave "mark to space" ratio of 1 to 1 is used,
		# then "wait" until a "space" is found.
		# (For those that don't know.)
		#
		#                  +------+      +---
		# Square wave:-    | Mark |Space |
		#               ---+      +------+
		#
		# This ensures that the loop cycles when NO input is
		# applied to the microphone socket.
		# Exit this loop when "mark" is found or n >= 8000...
		while [ $number -le 127 ]
		do
			number=`hexdump -n1 -s$subscript -v -e '1/1 "%u"' /tmp/sinewave.raw`
			subscript=$[ ( $subscript + 1 ) ]
			# Ensure as soon as subscript >= 8000 occurs it drops out of the loop.
			if [ $subscript -ge 8000 ]
			then
				break
			fi
		done
		# Ensure as soon as subscript >= 8000 occurs it drops completely out of this loop.
		if [ $subscript -ge 8000 ]
		then
			break
		fi
		# Now the "mark" can loop until a "space" is found again and the whole
		# can cycle until subscript >= 8000...
		while [ $number -ge 128 ]
		do
			number=`hexdump -n1 -s$subscript -v -e '1/1 "%u"' /tmp/sinewave.raw`
			subscript=$[ ( $subscript + 1 ) ]
			# Ensure as soon as subscript >= 8000 occurs it drops out of the loop.
			if [ $subscript -ge 8000 ]
			then
				break
			fi
		done
		# Ensure as soon as subscript >= 8000 occurs it drops completely out of this loop.
		if [ $subscript -ge 8000 ]
		then
			break
		fi
		# "freq" will become the frequency of a symmetrical waveform
		# when the above loops are finally exited, subscript >= 8000...
		# Tick up the freq(uency) per "mark to space" cycle.
		freq=$[ ( $freq + 1 ) ]
		done
	clear
	printf "\nA simple 50 Hz to 3500 Hz audio frequency counter.\n"
	printf "(C)2013, B.Walker, G0LCU. Issued as Public Domain.\n"
	printf "Accuracy is within 0.1 percent of the displayed frequency...\n"
	printf "\nFrequency is "$freq"Hz...\n\n"

done
# End of Freq_Counter.sh DEMO.
# Enjoy finding simple solutions to often very difficult problems.