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sr #110555: Obtain command status from DEBUG and RETURN trap

Submitter:  Dominik Kummer <domson>
Submitted:  Mon 25 Oct 2021 11:59:59 PM UTC
Category:  None Priority:  5 - Normal
Severity:  2 - Minor Status:  Works For Me
Privacy:  Public Assigned to:  None
Open/Closed:  Open Operating System:  GNU/Linux
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Mon 01 Nov 2021 10:22:59 PM UTC, comment #2: 

I see, in my mind it remained an irrefutable fact that the DEBUG trap is executed after a simple command. Most probably because it is written like so in a Bash Beginners Guide does explain it reliably.

It is a bit counterintuitive, but a workaround with a FIFO is possible though. It is because I need to highlight traced commands with certain status codes. So I have to print $BASH_COMMAND after it is executed.

Dominik Kummer <domson>
Mon 01 Nov 2021 07:08:43 PM UTC, comment #1: 

I don't understand the question. The DEBUG trap is always executed before a simple command, where BASH_COMMAND tells you what will be executed. Since it's run before the command, and $? always reflects the status of the last command run, it's always going to be the previous command.

Chet Ramey <chet>
Project Administrator
Mon 25 Oct 2021 11:59:59 PM UTC, original submission:  

I am writing a debugging helper which echoes traced functions and related commands during script execution.


$ trap 'status=$?; echo $LINENO $BASH_COMMAND [$status]' DEBUG;

echoes the traced command, but the status returns from the previous command. So as a result the status always lacks behind. Thats because $ 'status=$?'; captures the previous command's status, which is not $BASH_COMMAND itself.

$ false # gives two lines
224 false [0]
$ true # shows command but previous status
225 true [1]

Shouldn't the output look like the following?

$ false
224 false [1]
$ true
225 true [0]

Workarounds are possible but disproportionate complicated IMHO.

Dominik Kummer <domson>


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