Package: bash
Version: 4.2+dfsg-1
Severity: normal
Dear Bash Maintainer,
Bash seems to have a bug in which it cannot reset the signal handler
(using 'trap') when already within a signal handler. Here is a sample
script that demonstrates the problem:
----------------------------------------------------------------------
#
# ackbar.sh: a test of layered trap handling in Bourne-ish shells.
# In a working shell, this script should exit when ^C is hit twice.
#
trap maybeexit 2
maybeexit() {
trap reallyexit 2
echo
echo -n "Cancelling task $x"
sleep 1
echo
trap maybeexit 2
}
reallyexit() {
echo
echo "Okay, really exiting..."
exit 0
}
echo "Hit ^C to cancel current task."
echo "Hit ^C twice to exit."
while :; do
x=$((x+1))
echo "Now churning on long running task no. $x"
sleep 1000
done
----------------------------------------------------------------------
When run in Bash this script does not exit when ^C is hit twice. The
first ^C is caught correctly, but the second merely kills the "sleep"
in the "maybeexit" signal handler and continues execution. (Note:
Using the "trap -p" command before the sleep, one can see that Bash
actually thinks it has updated the signal handler, even though it does
not honor it.)
In contrast, when this script is run in other POSIX shells (I've
tested dash, ksh, mksh, pdksh, and zsh), the script runs correctly.
In those shells, hitting ^C twice calls the "reallyexit" signal handler
which exits the program.
I admit that there is much deep magic surrounding "correct" interrupt
handling in different shells, but I'm not inexperienced, and I'd be
very surprised if this is by design. If so, then there is a bug in the
documentation, as I have pored over it repeatedly and there is no
mention of traps being inoperable until the handler has finished.
--Ben
-- System Information:
Debian Release: jessie/sid
APT prefers stable-updates
APT policy: (500, 'stable-updates'), (500, 'testing'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386
Kernel: Linux 3.9-1-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Versions of packages bash depends on:
ii base-files 7.2
ii dash 0.5.7-3
ii debianutils 4.3.4
ii libc6 2.17-7
ii libtinfo5 5.9+20130608-1
Versions of packages bash recommends:
ii bash-completion 1:2.0-1
Versions of packages bash suggests:
ii bash-doc 4.2+dfsg-1
-- no debconf information
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