Re: Error code from a shell pipeline.
Tzafrir Cohen [EMAIL PROTECTED] writes:
On Fri, Oct 24, 2003 at 10:47:22PM +0200, Oleg Goldshmidt wrote:
Shlomi Fish [EMAIL PROTECTED] writes:
On Fri, 24 Oct 2003, Beni Cherniavsky wrote:
Shlomi Fish wrote on 2003-10-12:
I want that if one of the (first) components of the pipeline exits with an
error code, I'll know about it somehow. How?
info bash --index PIPESTATUS
Cool thanks.
Depending on your needs you may also use the -e option to the shell
(should work for most Bourne shell and csh descendants), the option
will make the shell exit if any of the commands in the pipeline fails.
$ true | false | true
$ echo $?
0
$ bash -e true | false | true
true | false | true: true | false | true: No such file or directory
$ echo $?
1
This is because you tried running a script from a file called
true | false | true
However:
$ set -e
$ true | false | true
$ echo $?
0
So setting that doesn't make an error from the middle of a pipe show.
Hmm, this seems to be true. What is weird about it, is that it is
supposed to do what I said. At least that is the way I used to read
the bash documentation and also the make documentation (which is where
I learned about -e from N years ago) - see below.
Check http://www.gnu.org/manual/make-3.77/html_node/make_43.html that
says
Here is the pattern rule to generate a file of dependencies (i.e., a
makefile) called `name.d' from a C source file called `name.c':
%.d: %.c
$(SHELL) -ec '$(CC) -M $(CPPFLAGS) $ \
| sed '\''s/\($*\)\.o[ :]*/\1.o $@ : /g'\'' $@; \
[ -s $@ ] || rm -f $@'
See section Defining and Redefining Pattern Rules, for information on
defining pattern rules. The `-e' flag to the shell makes it exit
immediately if the $(CC) command fails (exits with a nonzero
status). Normally the shell exits with the status of the last command
in the pipeline (sed in this case), so make would not notice a nonzero
status from the compiler.
Now, I created the following C file
#include foo.h
int main(void) { return 0; }
(cpp should fail because there is no foo.h), and the following
makefile:
%.d: %.c
$(SHELL) -ec '$(CC) -M $(CPPFLAGS) $ \
| sed '\''s/\($*\)\.o[ :]*/\1.o $@ : /g'\'' $@'
(I don't want foo.d removed if it contains nothing, otherwise it is
identical to the example in the manual).
Guess what: make does not notice a nonzero status from the compiler
with or without -e.
So I got curious, and added
SHELL := csh
to the makefile, and - lo and behold! - it worked (csh is a symbolic
link to tcsh, and it works for both).
Now, man tcsh says
-e The shell exits if any invoked command terminates
abnormally or yields a non-zero exit status.
To compare, man bash says (for set builtin)
-e Exit immediately if a simple command (see
SHELL GRAMMAR above) exits with a non-zero
status. The shell does not exit if the
command that fails is part of an until or
while loop, part of an if statement, part
of a or || list, or if the command's
return value is being inverted via !. A
trap on ERR, if set, is executed before the
shell exits.
Further RTFMing (man bash is at your service) uncovered that bash
distinguishes between simple commands, pipelines, and lists, and the
-e applies to simple commands only, as per above.
So it turns out that bash and tcsh behave differently. I apologize for
my misleading post - it only applies to t?csh, it seems, not to bash
(nor to zsh). I find it rather curious that the make documentation
does not mention the difference.
Now, I don't know what the rationale for bash behaviour is. It seems
to me that the way tcsh behaves is pretty useful.
--
Oleg Goldshmidt | [EMAIL PROTECTED]
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Re: Error code from a shell pipeline.
On Saturday 25 October 2003 14:47, Oleg Goldshmidt wrote: Now, I don't know what the rationale for bash behaviour is. It seems to me that the way tcsh behaves is pretty useful. Probably some POSIX compliance requirement. I'm too lazy to search now GO-SOLO - The single Unix specification, but may do it later under sufficient pressure :-) -- Oron Peled Voice/Fax: +972-4-8228492 [EMAIL PROTECTED] http://www.actcom.co.il/~oron Normal people ... believe that if it ain't broke, don't fix it. Engineers believe that if it ain't broke, it doesn't have enough features ... yet. -- Scott Adams = To unsubscribe, send mail to [EMAIL PROTECTED] with the word unsubscribe in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
Re: Error code from a shell pipeline.
Shlomi Fish wrote on 2003-10-12:
I want that if one of the (first) components of the pipeline exits with an
error code, I'll know about it somehow. How?
info bash --index PIPESTATUS
$ true | false | true | false; echo [EMAIL PROTECTED]
0 1 0 1
$ { true | false | true | false; }; echo [EMAIL PROTECTED]
0 1 0 1
However, using parenthesis you launch the whole pipeline in a subshell
so it won't work:
$ ( true | false | true | false; ); echo [EMAIL PROTECTED]
1
Also, it mysteriously seems to be lost after every command in
interactive mode:
$ true | false | true | false
$ echo [EMAIL PROTECTED]
0
Although it does work in non-interactive mode:
$ echo $'true | false | true | false\necho [EMAIL PROTECTED]' | sh
0 1 0 1
If you want a less fragile approach, Oded Arbel gave a good advice.
--
Beni Cherniavsky [EMAIL PROTECTED]
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Re: Error code from a shell pipeline.
On Fri, 24 Oct 2003, Beni Cherniavsky wrote:
Shlomi Fish wrote on 2003-10-12:
I want that if one of the (first) components of the pipeline exits with an
error code, I'll know about it somehow. How?
info bash --index PIPESTATUS
Cool thanks.
$ true | false | true | false; echo [EMAIL PROTECTED]
0 10 1
$ { true | false | true | false; }; echo [EMAIL PROTECTED]
0 1 0 1
However, using parenthesis you launch the whole pipeline in a subshell
so it won't work:
$ ( true | false | true | false; ); echo [EMAIL PROTECTED]
1
Also, it mysteriously seems to be lost after every command in
interactive mode:
$ true | false | true | false
$ echo [EMAIL PROTECTED]
0
Works for me:
shlomi:~$ true | false | false | true
shlomi:~$ echo [EMAIL PROTECTED]
0 1 1 0
Maybe you execute some command after every prompt.
Although it does work in non-interactive mode:
$ echo $'true | false | true | false\necho [EMAIL PROTECTED]' | sh
0 1 0 1
Wow, I wasn't aware of the $'' construct. I guess you learn something new
every day. :-)
If you want a less fragile approach, Oded Arbel gave a good advice.
This approach is also dependent on the user shell being bash. I am using
this shell call from a Perl script. In any case, I eliminated the pipeline
from the command and now this is no longer relevant.
Thanks anyway.
Regards,
Shlomi Fish
--
Shlomi Fish[EMAIL PROTECTED]
Home Page: http://t2.technion.ac.il/~shlomif/
Writing a BitKeeper replacement is probably easier at this point than getting
its license changed.
Matt Mackall on OFTC.net #offtopic.
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Re: Error code from a shell pipeline.
Shlomi Fish [EMAIL PROTECTED] writes: On Fri, 24 Oct 2003, Beni Cherniavsky wrote: Shlomi Fish wrote on 2003-10-12: I want that if one of the (first) components of the pipeline exits with an error code, I'll know about it somehow. How? info bash --index PIPESTATUS Cool thanks. Depending on your needs you may also use the -e option to the shell (should work for most Bourne shell and csh descendants), the option will make the shell exit if any of the commands in the pipeline fails. $ true | false | true $ echo $? 0 $ bash -e true | false | true true | false | true: true | false | true: No such file or directory $ echo $? 1 -- Oleg Goldshmidt | [EMAIL PROTECTED] = To unsubscribe, send mail to [EMAIL PROTECTED] with the word unsubscribe in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
Re: Error code from a shell pipeline.
On Fri, Oct 24, 2003 at 10:47:22PM +0200, Oleg Goldshmidt wrote: Shlomi Fish [EMAIL PROTECTED] writes: On Fri, 24 Oct 2003, Beni Cherniavsky wrote: Shlomi Fish wrote on 2003-10-12: I want that if one of the (first) components of the pipeline exits with an error code, I'll know about it somehow. How? info bash --index PIPESTATUS Cool thanks. Depending on your needs you may also use the -e option to the shell (should work for most Bourne shell and csh descendants), the option will make the shell exit if any of the commands in the pipeline fails. $ true | false | true $ echo $? 0 $ bash -e true | false | true true | false | true: true | false | true: No such file or directory $ echo $? 1 This is because you tried running a script from a file called true | false | true However: $ set -e $ true | false | true $ echo $? 0 So setting that doesn't make an error from the middle of a pipe show. -- Tzafrir Cohen +---+ http://www.technion.ac.il/~tzafrir/ |vim is a mutt's best friend| mailto:[EMAIL PROTECTED] +---+ = To unsubscribe, send mail to [EMAIL PROTECTED] with the word unsubscribe in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
Error code from a shell pipeline.
$ make || echo hello make: *** No targets specified and no makefile found. Stop. hello But OTOH: (make | echo) || echo hello make: *** No targets specified and no makefile found. Stop. And also: $ (echo | make) || echo hello make: *** No targets specified and no makefile found. Stop. hello I want that if one of the (first) components of the pipeline exits with an error code, I'll know about it somehow. How? Regards, Shlomi Fish -- Shlomi Fish[EMAIL PROTECTED] Home Page: http://t2.technion.ac.il/~shlomif/ Writing a BitKeeper replacement is probably easier at this point than getting its license changed. Matt Mackall on OFTC.net #offtopic. = To unsubscribe, send mail to [EMAIL PROTECTED] with the word unsubscribe in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
Re: Error code from a shell pipeline.
On Sunday 12 October 2003 18:38, Shlomi Fish wrote: (make | echo) || echo hello make: *** No targets specified and no makefile found. Stop. I want that if one of the (first) components of the pipeline exits with an error code, I'll know about it somehow. How? an erronouse exit code (actually, just not true) does not break the pipe. how about (make || echo oops 2 ) | cat-or-something -- Oded ::.. 'I have been told that Introduction to Objectivist Epistemology was required reading at the Xerox PARC lab where OOP was invented, but this may be merely an urban legend.' -- Bryce Wilcox = To unsubscribe, send mail to [EMAIL PROTECTED] with the word unsubscribe in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
