Re: [Help-bash] Bash is setting disposition of a signal, ignored upon entry to shell, to default

[Anoop Sharma]

Today I tested with:  GNU bash, version 4.2.42(1)-release (i686-pc-linux-gnu)

However, the script still failed for me when I do not include any sha-bang line in the script and run the script as - "./test_1.sh".  

The script works as expected when run as "bash -c ./test_1.sh" and also passes when #!/bin/bash is included in the script.

With Thanks,

Anoop

On Fri, Jan 11, 2013 at 1:13 AM, Chet Ramey <address@hidden> wrote:

On 1/10/13 11:42 AM, Chet Ramey wrote:
> On 1/9/13 4:09 PM, Anoop Sharma wrote:
>> Using: GNU bash, version 4.2.24(1)-release (i686-pc-linux-gnu)
>>
>> I ignore a signal using trap command on an interactive shell. I expect that
>> signal to remain ignored in the script started from the same shell.
>> However, I find disposition of that signal reset to default, even though
>> trap command in the script shows that signal is ignored.
>>
>> I am not sure if this is the right behavior. Please help.
>>
>>
>> Step 1 - Ignore the signal by typing the following command on an
>> interactive shell
>> ----------
>> $ trap '' SIGXFSZ
>>
>> Step 2 - Given below is a script that starts a sleep in the background and
>> then sends the signal to that sleep to test if the signal terminates the
>> sleep or not.
>> ---------
>> $ cat test_1.sh
>> trap
>> sleep 30&
>> sleep 1
>> pid=$!
>> kill -s SIGXFSZ $pid
>>
>> sleep 1
>> kill -0 $pid && echo "sleep survived the signal" && exit
>> echo "sleep was terminated by the signal"
>> $
>>
>> Step 3 - Even though the disposition of the signal was set to ignore in the
>> Step 1 (and first line of the output of script confirms that), yet, the
>> sleep is terminated by the signal. Is it right?

OK, pretty much everything I wrote before was wrong.  I should learn not to
answer these things so quickly.

I tested the script a little more, adding a program that just prints
signal dispositions, and discovered that:

1.  The subshell/script does inherit the SIG_IGN disposition for SIGXFSZ.
2.  The subshell/script does invoke programs with the SIG_IGN disposition
    for SIGXFSZ.
3.  The script, when run, displays "sleep survived the signal".

I tested bash-4.2.42 on RHEL 5 and Mac OS X.

Chet

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