UNIX for Dummies Questions & Answers

Not sure if this is of any use but......

I was messing around with getting return codes greater than 255 for special usage...

Of course the code could be made simple but in this code the new stored return code
is generated as exit is progressing...

Code:

#!/bin/sh
# Real and imaginary return codes...
> /tmp/return.code
imaginary_return_code=1234567890
RC=0
while true
do
	# Do some stuff and......
	# Generate your real RC value to exit with 0 to 254.
	# Generate your imaginary value to exit with 255 to 2147483647, add text too IF required.
	if [ $imaginary_return_code -ge 255 ]
	then
		RC=255
	fi
	if [ $RC -eq 255 ]
	then
		exit $RC $( printf "Error number $imaginary_return_code:- Idiot at the keyboard\!" > /tmp/return.code )
	else
		exit $RC
	fi
done

Results on OSX 10.7.5, default shell...

Code:

Last login: Wed Oct 23 22:15:16 on ttys000
AMIGA:barrywalker~> ./RC.sh
AMIGA:barrywalker~> RC="$?"
AMIGA:barrywalker~> echo "$RC"
255
AMIGA:barrywalker~> read RC < /tmp/return.code
AMIGA:barrywalker~> echo "$RC"
Error number 1234567890:- Idiot at the keyboard!
AMIGA:barrywalker~>

It's not clear what you are doing or what you are asking. Give more context and expected behavior.

I don't see any questions in this post but in bash, an exit value of 1234567890 will always return 210 (1234567890 modulo 256).

Exit codes are 0-255, feeding it a 256 will give you a 0. The output stream is usually used for the actual data.

The exit status from a command is the result of the syscall wait() or waitpid(). When the child process returns it pushes a value onto the stack - the parent reads the return value.
But it only sees the lower eight bits of the value -- 0 -> 255 if you consider the return value an integer.

I would commend to your attention sysexits.h which is an attempt to do what you seem to want to do.

Exit status - Wikipedia, the free encyclopedia

Hi guys...

This was just an idea...

I wasn't actually asking anything. I was experimenting with generating an error code
system of my own with values outside of an 8 bit range.
I used the real 255 exit code as 'number out of range' flag and then generate a string
whilst exit is in process. This string was originally a number, but I decided to make it
a string instead, purely for fun.

It is immediately stored for checking later.

It works for me and I thought it might work for others.

Anyhow thanks for the feedback.

Perhaps I shouldn't have posted it...

I am not sure if this will work in any way: return codes are not coming out of thin air, but the result of a system call, as jim mcNamara has explained. It can't give you back more than it ought to. It is defined as an unsigned 8-bit integer, so it can't deliver a 16- (or 32-, 64-, ...) bit number, a string or whatever. This would mean that this value has to be put on the stack and then pulled off it by the wait() or waitpid()-function. As the function would not know that it is expected to get that off the stack it won't do it and the stack would be (and stay) subsequently corrupted.

If you want to have extended exit-messages of any sort - strings, numbers, whatever - you will have to use the classical means of conveying such messages: interprocess communication (aka semaphores, shared memory segments, ... - take your pick) or process-to-process I/O, like file descriptors and/or named pipes. Write to <stdout>, <stderr>, etc. and intercept this with pipes, I/O-redirection and the like.

Another option is to write to a log file of some sort and have that parsed from the calling process.

There is no harm done in discussing anything and i am convinced this board won't go down from 1k characters of non-conclusive discussion. Still, i think you should post such topics (and the likes - you seem to enjoy exploring the limits of the OS in general and the shell in specific) not in the beginner forum. This is clearly not the stuff someone who learned the shell yesterday asks first. Please consider moving to the experts forum for topics like this.

I hope this helps.

bakunin