exec'ing $0 in traps

exec'ing $0 in traps

[Andre Albsmeier]

When sending SIGHUP to this script:

#!/bin/zsh

echo started
trap 'echo trapped; exec "$0"' 1

echo $$ > /tmp/blafasel

while read line; do
  echo line $line
done


restarting works exactly one time and then no more. With
FreeBSD's native /bin/sh or even the lousy /bin/bash it
works as expected.

What am I doing wrong?

	-Andre

Re: exec'ing $0 in traps

[Bart Schaefer]

On Feb 17,  9:16am, Andre Albsmeier wrote:
}
} #!/bin/zsh
} 
} echo started
} trap 'echo trapped; exec "$0"' 1
} 
} echo $$ > /tmp/blafasel
} 
} while read line; do
}   echo line $line
} done

Some combination of the "read" builtin plus calling "exec" from inside
the signal handler is causing the HUP signal to remain blocked across
the "exec" -- and re-installing the trap doesn't unblock it.

If I replace the read-loop with

    sleep 3
    kill -1 $$

then the process restarts itself every 3 seconds as expected.

So, you aren't doing anything explicitly wrong.

Re: exec'ing $0 in traps

[Andre Albsmeier]

On Fri, 17-Feb-2017 at 12:02:19 -0800, Bart Schaefer wrote:
> On Feb 17,  9:16am, Andre Albsmeier wrote:
> }
> } #!/bin/zsh
> } 
> } echo started
> } trap 'echo trapped; exec "$0"' 1
> } 
> } echo $$ > /tmp/blafasel
> } 
> } while read line; do
> }   echo line $line
> } done
> 
> Some combination of the "read" builtin plus calling "exec" from inside
> the signal handler is causing the HUP signal to remain blocked across
> the "exec" -- and re-installing the trap doesn't unblock it.

Too bad. Maybe this gets fixed one day. Meanwhile I use this:

#!/bin/zsh

restart=""
echo started

trap 'restart=1' 1

echo $$ > /tmp/blafasel

while :; do
  [ $restart ] && exec $0
  read line || exit 0
  echo line $line          
done


and it seems to do what I need...