OS X (Apple)

Hi bakunin...
Thanks I will use that method in future code.
I used what I knew would work as my starting point but I wanted a lookup array instead and Don gave me what I wanted...

Don...
I was aware of $V remaining and I will take any errors into account by initialising $V to 0 per call. I will initialise $num too and ensure that is always present.
I will be using a _re-usable_variable_ for $V as once it has been used it will not be needed again until the routine is called and can be used elsewhere. (yeah I know try not to use re-usable variables, but I only have 4 and I know what they are and commented on them inside AudioScope.sh)...

Thanks muchly for tour guidance...

Bazza.

The test -a and -o binary operators aren't required on all POSIX systems (but are currently required on a UNIX branded systems). With some expressions -a and -o can lead to ambiguities in the grammar; so they are likely to be deprecated in the next revision of the POSIX standards. (That doesn't mean that they'll every actually be removed from the shells, but the shell developers all advise against using them.)

Fortunately, test and [ are built-ins in current shells so you don't actually have to fork and exec /usr/bin/test twice so the penalty for using test twice isn't nearly as high as it was in early shells.

On OS X (which is what wisecracker is using), both bash and ksh support the command:

Code:

if [[ num >= 100 && num <= 199 ]]

which is handled as part of the shell's grammar, not as a built-in utility (which makes it even faster and gets rid of the ambiguity in the test syntax). This form isn't in the standards yet, but is also likely to be added in the next revision.

Right guys...

The code below is a working example of the real DC voltage input with the output read off of a professional frequency counter. (The builtin counter inside AudioScope.sh works just as well but I needed to work out the calibration method so I tested the board on the bench at work. [ Shhhh, don't tell anyone... ;o) ]
The values of '$freq' were rounded up or down to the nearest 0 or 5...
The board has had one very minor modification, a 1M resistor added.
The code below is working a dream, thank you Don...
A highly mofified version will be incorporated into the main code over the WE...

Code:

#!/bin/bash
# lookup
freq=( 0 860 945 1025 1110 1190 1275 1355 1445 1520 1605 1685 1770 1855 1940 2025 2110 2200 4000 )
voltage=( 0.000 0.000 0.125 0.250 0.375 0.500 0.625 0.750 0.875 1.000 1.125 1.250 1.375 1.500 1.625 1.750 1.875 2.000 0.000 )
while true
do
	read -p "Simulate frequency from AudioScope builtin counter, 0 to 3999:- " num
	for ((i=0; i < ${#freq[@]}; i++))
	do
		[ "$num" -lt ${freq[i]} ] && break
	done
	[ $i -gt 0 ] && [ $i -lt ${#freq[@]} ] && V="${voltage[$i]}"
	echo "$V Volts DC..."
done