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 $pid
}
(
echo "in subshell"
tail -f /etc/motd &
pid=3D$!
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=20
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=20
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.
--=20
There has been only one Christian.
They caught him and crucified him -- early.
- Mark Twain
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