Date: Fri, 5 Sep 2003 14:14:36 -0400 From: The Anarcat <anarcat@anarcat.ath.cx> To: FreeBSD Questions <freebsd-questions@FreeBSD.ORG> Cc: anarcat@anarcat.ath.cx Subject: bug in sh or misinterpretation? Message-ID: <20030905181436.GF514@inso.ath.cx>
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[please CC, I don't follow -questions]
Hello!
I've been struggling with an odd quirk in sh(1). Here is my sample
code:
--- 8< cut here 8< ---
cleanup () {
echo "cleaning up $pid"
kill $pid
}
(
echo "in subshell"
tail -f /etc/motd &
pid=$!
trap cleanup 1 2 15
wait $pid || echo "command failed"
) &
wait
--- 8< cut here 8< ---
The idea is to be able *in the subshell* to cleanup a backgrounded
command. The result is unexpected:
anarcat@shall[~/src/local/bin/worldtools]% sh test_trap.sh
in subshell
FreeBSD 4.8-STABLE (SHALL) #0: Wed Aug 13 16:46:04 EDT 2003
Welcome to Shall, multi-purpose file/mail/web/ftp server.
^C
anarcat@shall[~/src/local/bin/worldtools]% ps
PID TT STAT TIME COMMAND
14162 p1 Ss 0:03,95 -zsh (zsh)
16918 p1 S 0:00,00 sh test_trap.sh
16919 p1 S 0:00,00 sh test_trap.sh
16920 p1 S 0:00,01 tail -f /etc/motd
16922 p1 R+ 0:00,00 ps
i.e. the subshell doesn't call the trap!! I've searched long and large
manuals, I even tried debugging (i'm about to build sh with debugging
symbols now): the subshell *really* receives the signal, it just
ignores it.
The sh manpage says that:
When the shell forks off a subshell, it resets trapped (but not
ignored) signals to the default action. The trap command has no
effect on signals that were ignored on entry to the shell.
Well, it looks like calling trap in the subshell doesn't work.
For reference, in bash and zsh behave correctly:
anarcat@shall[~/src/local/bin/worldtools]% zsh test_trap.sh
in subshell
FreeBSD 4.8-STABLE (SHALL) #0: Wed Aug 13 16:46:04 EDT 2003
Welcome to Shall, multi-purpose file/mail/web/ftp server.
^Ccleaning up 16947
anarcat@shall[~/src/local/bin/worldtools]% command failed
Is it me? Or do I head for GNATS? :)
A.
--
There has been only one Christian.
They caught him and crucified him -- early.
- Mark Twain
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