[Gllug] show non-zero exit code in bash

[Greater London Linux User Group]

Dean Wilson <dwilson at unixdaemon.net> writes:

> On Wed, Dec 28, 2005 at 06:21:04PM +0000, Tethys wrote:
>> 	show_exit_code()
>> 	{
>> 		retval=$?
>> 		cmdnum="$(history 1 | sed 's/\(^[0-9 ]*\).*/\1/')"
>> 		if [ $retval -ne 0 -a "$cmdnum" != "$lastcmdnum" ]
>> 		then
>> 			lastcmdnum="$cmdnum"
>> 			echo "Exit code: $retval"
>> 		fi
>> 	}
>
> show_exit_code() {
>   retval=$?
>   if [ $retval -ne 0 -a "$HISTCMD" != "$lastcmdnum" ];then
>     lastcmdnum="$HISTCMD"
>     echo " -- exit code: $retval"
>   fi
> }
>
> I've tweaked it a bit (and reformatted it to suit my .bash_profile) and
> by using $HISTCMD I can drop the two external commands
>
>> This also handles the corner cases:
>> - Successive commands with non-zero exit codes
>> - "Null commands", i.e., pressing return at the shell prompt
>
> Which is what my initial version failed to deal with.
>
> A pint is yours to claim Mr Tethys!

This still doesn't quite work. It solves the mentioned cases but adds
one of its own, namely that if you run the same command again and again
(after recompiling elsewhere, for example) HISTCMD is not updated, even
if you don't set HISTCONTROL to ignoredups. The solution to this is to
return to the former, only you can lose the sed thusly:

    show_exit_code() {
	retval=$?
	cmdnum="$(history 1)"
	cmdnum=$((${cmdnum:0:5}))
	if [ $retval -ne 0 -a "$cmdnum" != "$lastcmdnum" ]; then
	    lastcmdnum="$cmdnum"
	    echo -e "\033[1;31mCommand ($cmdnum) failed with exit code:" \
		"\033[1;35m$retval\033[0m"
	fi
    }

Incidentally you can do some very cool stuff with the $ symbol - search
for Parameter Expansion in the bash manpage.

This also solves the other corner case of it not being colourful :-)
Unfortunately, though, it won't work if you have history control set to
ignoredups, so it's still not perfect.

And I can't to find a way to reduce the two cmdnum= lines to one.

Matthew

-- 
I must take issue with the term "a mere child," for it has been my
invariable experience that the company of a mere child is infinitely
preferable to that of a mere adult.
                                           --  Fran Lebowitz
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