Re: return bultin ignores explicit exit value when used in DEBUG trap

[Chet Ramey]

On 11/19/15 2:06 AM, Grisha Levit wrote:
> Not sure if this is a documentation bug or a functional one, but the man page 
> does not seem to agree with the observed behavior for return when invoked in 
> DEBUG traps.

Thanks for the report.  The internal trap handler used for DEBUG and other
signals the shell treats specially needed to pick up the argument supplied
to `return' as well as noting `return' was called.

This affects the DEBUG, RETURN, and ERROR traps.

Chet
-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRUc...@case.eduhttp://cnswww.cns.cwru.edu/~chet/

return bultin ignores explicit exit value when used in DEBUG trap

[Grisha Levit]

Not sure if this is a documentation bug or a functional one, but the man page 
does not seem to agree with the observed behavior for return when invoked in 
DEBUG traps.

return [n]
   Causes a function to stop executing and return the value specified
   by n to its caller.  If n is omitted, the return status is that of 
   the last command executed in the function body.
   ...
   If return is executed by a trap handler, the last command used to 
   determine the status is the last command executed before the trap 
   handler.
   ...
   If  return  is executed during a DEBUG trap, the last command used 
   to determine the status is the last command executed by the trap 
   handler before return was invoked.



It seems that when return is used in a DEBUG trap, any explicit return value 
used is ignored.

For example:

fun1() { trap "trap - DEBUG; (exit 1); return"   DEBUG; :; }
fun1; echo $?  # 1, as expected

fun2() { trap "trap - DEBUG; (exit 1); return 2" DEBUG; :; }
fun2; echo $?  # also 1!


The man page doesn't mention anything about the RETURN trap, but it seems to 
function the same way as the DEBUG trap does in this regard.

fun3() { trap 'trap - RETURN; (exit 1); return 2' RETURN; (exit 3); return 
4; }
fun3; echo $?  # also 1!



There's also a minor inconsistency between the help topic and the man page 
regarding which traps are inherited when functrace is on:

 -T  If  set,  any traps on DEBUG and RETURN are inherited by
  shell functions,  command  substitutions,  and  commands
  executed  in  a  subshell  environment.   The  DEBUG and
  RETURN traps are normally not inherited in such cases.

 -T  If set, the DEBUG trap is inherited by shell functions.