killed by signal

killed by signal

[Atom Smasher]

if i understand it correctly... if zsh (or most/all other shells) spawns a 
process that is "terminated" by a signal, the exit status returned (to?) 
by the shell is 128+SIGNAL. but what about processes that are 
stopped/suspended by signals (most likely ^Z, on the command line)? if a 
process is stopped/suspended by a ^Z, is there *any* way for the parent 
shell to figure out if the process was suspended? or to differentiate if 
the return status just happens to be the same as a TSTP signal number?

thanks...


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Re: killed by signal

[Peter Stephenson]

On Mon, 6 Apr 2009 20:27:42 +1200 (NZST)
Atom Smasher <atom@smasher.org> wrote:
> if i understand it correctly... if zsh (or most/all other shells) spawns a 
> process that is "terminated" by a signal, the exit status returned (to?) 
> by the shell is 128+SIGNAL. but what about processes that are 
> stopped/suspended by signals (most likely ^Z, on the command line)? if a 
> process is stopped/suspended by a ^Z, is there *any* way for the parent 
> shell to figure out if the process was suspended? or to differentiate if 
> the return status just happens to be the same as a TSTP signal number?

$jobstates (from zsh/parameter) tells you.  If that's not the answer you'll
have to give more details about what you're actually trying to do (which is
often the way to get the most useful results).

% sleep 10 &
[1] 2117
% kill -TSTP %1
[1]  + suspended  sleep 10
% print $jobstates
suspended:+:2117=suspended

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR PLC, Churchill House, Cambridge Business Park, Cowley Road
Cambridge, CB4 0WZ, UK                          Tel: +44 (0)1223 692070

Re: killed by signal

[Atom Smasher]

On Mon, 6 Apr 2009, Peter Stephenson wrote:

> $jobstates (from zsh/parameter) tells you.  If that's not the answer 
> you'll have to give more details about what you're actually trying to do 
> (which is often the way to get the most useful results).
===============

i can use the return status to figure out if a command was "terminated" by 
a signal, and which signal was the killer... 128+9 = 137 == KILL. i know 
the command immediately preceding the precmd was KILLed.

but if a command is suspended (TSTP; 20 on linux, 18 on freebsd) precmd 
will see a return status <128, which could be a "legal" value for a 
command to return indicating a particular failure. i'd like precmd to 
distinguish between a command that returns 18 or 20 (freebsd or linux, 
respectively), and a command that is suspended with ^Z.

specific example... on freebsd i can get a return status of 18 either by 
suspending a job with ^Z, or running:
 	zip -MM foo.zip no-such-file
  so the question is: how can the shell (can the shell?) tell that one of 
those was suspended with a signal (^Z, TSTP), and zip which is indicating 
a specific failure (zip: "File not found").

for a few seconds i thought the ERRNO might be useful, but it seems to not 
be.

thanks...


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         ...atom

  ________________________
  http://atom.smasher.org/
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 		President of the United States, 1919

Re: killed by signal

[Atom Smasher]

On Tue, 7 Apr 2009, Atom Smasher wrote:

> but if a command is suspended (TSTP; 20 on linux, 18 on freebsd) precmd 
> will see a return status <128, which could be a "legal" value for a 
> command to return indicating a particular failure. i'd like precmd to 
> distinguish between a command that returns 18 or 20 (freebsd or linux, 
> respectively), and a command that is suspended with ^Z.
>
> specific example... on freebsd i can get a return status of 18 either by 
> suspending a job with ^Z, or running:
> 	zip -MM foo.zip no-such-file
>  so the question is: how can the shell (can the shell?) tell that one of 
> those was suspended with a signal (^Z, TSTP), and zip which is 
> indicating a specific failure (zip: "File not found").
=========================

here's a hack.... after a command is suspended, $? is updated but 
$pipestatus isn't. so if
 	[[ ${?} != ${${=pipestatus}[-1]} ]]
  then the preceding command must have been suspended.

but it doesn't work all the time: if a command returns with an exit status 
equal to a suspend signal (which is probably rare), and the next command 
is suspended with that signal, that would result in a false negative; 
failing to detect that a command was suspended... but most of the time it 
should work, and i don't think it's possible to get a false positive.

if anyone has a better way to do it...


-- 
         ...atom

  ________________________
  http://atom.smasher.org/
  762A 3B98 A3C3 96C9 C6B7 582A B88D 52E4 D9F5 7808
  -------------------------------------------------

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