Bruno Haible <br...@clisp.org> writes:
> Ben Pfaff wrote:
>> I still see the "broken pipe" error with it.
>
> Could you please investigate, by using strace, looking at signal masks of
> processes, etc.? This "broken pipe" issue in bash is becoming extremely
> unsatisfying. We have the world-class shell programming experts on this
> mailing list and *still* don't understand how SIGPIPE works?!
I took a closer look, as you asked:
b...@blp:~/tmp(0)$ bash --version
GNU bash, version 3.2.48(1)-release (i486-pc-linux-gnu)
Copyright (C) 2007 Free Software Foundation, Inc.
Default handling of SIGPIPE
---------------------------
b...@blp:~/tmp(0)$ strace -o foo -f bash
b...@blp:~/tmp(0)$ trap - SIGPIPE
b...@blp:~/tmp(0)$ grep ^Sig /proc/$$/status
SigQ: 1/16382
SigPnd: 0000000000000000
SigBlk: 0000000000010000
SigIgn: 0000000000384000
SigCgt: 000000004b813eff
SigIgn: ...4000 means SIGPIPE is not SIG_IGN.
SigCgt: ...3eff means SIGPIPE has a registered handler.
b...@blp:~/tmp(0)$ echo hi | ./a.out
bash: echo: write error: Broken pipe
b...@blp:~/tmp(1)$ exit
So, "foo" shows what happened:
21287 write(1, "hi\n", 3) = -1 EPIPE (Broken pipe)
21287 --- SIGPIPE (Broken pipe) @ 0 (0) ---
21287 sigreturn() = ? (mask now [])
21287 write(2, "bash: echo: write error: Broken "..., 37) = 37
21287 exit_group(1) = ?
bash caught the signal, returned from the handler (returning
EPIPE from the write call, I guess), printed the error message,
and exited.
Ignoring SIGPIPE
----------------
This seems interesting at least for completeness.
b...@blp:~/tmp(0)$ strace -o bar -f bash
b...@blp:~/tmp(0)$ trap '' SIGPIPE
b...@blp:~/tmp(0)$ grep ^Sig /proc/$$/status
SigQ: 1/16382
SigPnd: 0000000000000000
SigBlk: 0000000000010000
SigIgn: 0000000000385000
SigCgt: 000000004b812eff
SigIgn: ...5000 means SIGPIPE is SIG_IGN.
b...@blp:~/tmp(0)$ echo hi | ./a.out
bash: echo: write error: Broken pipe
b...@blp:~/tmp(1)$ exit
This time "bar" shows what happened:
21313 rt_sigaction(SIGPIPE, {0x1, [], 0}, {0x1, [], 0}, 8) = 0
0x1 is SIG_IGN.
21313 rt_sigaction(SIGTERM, {SIG_DFL, [], 0}, {0x1, [], 0}, 8) = 0
21313 rt_sigaction(SIGCHLD, {SIG_DFL, [], 0}, {0x807f600, [], 0}, 8) = 0
21313 pipe([3, 4]) = 0
21313 close(3) = 0
21313 close(4) = 0
21313 rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
21313 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
21313 rt_sigaction(SIGCHLD, {0x807f600, [], 0}, {SIG_DFL, [], 0}, 8) = 0
21313 rt_sigaction(SIGINT, {0x8094050, [], 0}, {SIG_DFL, [], 0}, 8) = 0
21313 rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
21313 write(1, "hi\n", 3) = -1 EPIPE (Broken pipe)
21313 --- SIGPIPE (Broken pipe) @ 0 (0) ---
(The SIGPIPE never gets to the process--it was ignored--but
ptrace() and hence strace reports it anyway. You can tell that
bash didn't receive it in this case because the log shows no call
to sigreturn().)
21313 write(2, "bash: echo: write error: Broken "..., 37) = 37
21313 exit_group(1) = ?
So in this case bash just gets the EPIPE directly, prints the
error message, and exits.
Conclusion
----------
I don't see a way to avoid this with using "echo" in bash 3.2.
Your gnulib-tool comment refers to Chet Ramey's email at
http://lists.gnu.org/archive/html/bug-bash/2008-12/msg00050.html.
I think that he is saying the same thing, actually:
The second is that the echo builtin in bash-3.2 displays a message on
a write error, instead of letting the exit status communicate the error.
When the shell receives SIGPIPE and handles it without exiting, writes
to that pipe return -1/EPIPE, and the echo builtin reports the error. In
earlier versions, you wouldn't have seen the message.
The bash 3.2 "printf" builtin doesn't have this problem though.
So, here's a new proposed patch. It does fix the problem for me.
commit 7357b5f06c00889037edfc433f1601cba42ba22c
Author: Ben Pfaff <b...@cs.stanford.edu>
Date: Sat Feb 20 22:09:58 2010 -0800
Avoid "broken pipe" message from lseek test.
* m4/lseek.m4: Use "printf" instead of "echo" to avoid "Broken
pipe" message from bash 3.2 "echo" builtin.
diff --git a/ChangeLog b/ChangeLog
index 9d3367e..a6c86b5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2010-02-20 Ben Pfaff <b...@cs.stanford.edu>
+
+ Avoid "broken pipe" message from lseek test.
+ * m4/lseek.m4: Use "printf" instead of "echo" to avoid "Broken
+ pipe" message from bash 3.2 "echo" builtin.
+
2010-02-19 Bruno Haible <br...@clisp.org>
Make it easier to find modules. New gnulib-tool option '--find'.
diff --git a/m4/lseek.m4 b/m4/lseek.m4
index f308495..39bbd64 100644
--- a/m4/lseek.m4
+++ b/m4/lseek.m4
@@ -1,4 +1,4 @@
-# lseek.m4 serial 4
+# lseek.m4 serial 5
dnl Copyright (C) 2007, 2009, 2010 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
@@ -21,7 +21,7 @@ int main ()
}],
[if test -s conftest$ac_exeext \
&& ./conftest$ac_exeext < conftest.$ac_ext \
- && { echo hi | ./conftest$ac_exeext; test $? = 1; }; then
+ && { printf hi | ./conftest$ac_exeext; test $? = 1; }; then
gl_cv_func_lseek_pipe=yes
else
gl_cv_func_lseek_pipe=no
--
Ben Pfaff
http://benpfaff.org
