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_piped=True swallows exceptions/errors #309

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mattixpet opened this issue Apr 6, 2016 · 1 comment
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_piped=True swallows exceptions/errors #309

mattixpet opened this issue Apr 6, 2016 · 1 comment

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@mattixpet
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Using _piped=True seems to swallow exceptions and log nothing even when there are errors in the piped commands. A very simple example is straight from the docs:

for line in sh.tr(sh.tail("-f", "test.log", _piped=True), "[:upper:]", "[:lower:]", _iter=True):
    print(line)

If test.log does not exist, tail understandably throws an exception in a normal shell and run on it's own using sh in python

/usr/bin/tail: cannot open ‘test.log’ for reading: No such file or directory
/usr/bin/tail: no files remaining

However, if you use it in piping you get no error and no logging.

A simple workaround for the logging is adding _err=myCallback and having myCallback manually printing out the errors, but that still doesn't handle the disappearance of the exceptions.

Is this intended behavior? This should at least be mentioned in the docs, if not fixed.

@amoffat
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amoffat commented Oct 9, 2016

ok I think I have a fix for this in the release-1.2 branch now. The issue is not really a bug, per-se, but not ideal and definitely not documented.

The behavior in release-1.2 is that if a process is launched that is not waited, and its used as stdin to a process that is waited on, the outer process, and its termination, will do some exception checking on the inner process, so any exceptions that occurred in the inner process will bubble up to the main thread and can be caught. In the cases where a process is launched that is not waited on, but is not used as stdin...there's no good way to bubble up those exceptions to the main thread, so we just cause them to raise inside of its internal threads, which will at least print something to the screen.

@amoffat amoffat closed this as completed Oct 9, 2016
@amoffat amoffat modified the milestone: 1.2 Oct 25, 2016
@amoffat amoffat removed the 1.2 label Oct 25, 2016
0-wiz-0 added a commit to NetBSD/pkgsrc-wip that referenced this issue Dec 12, 2016

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*   added `_out` and `_out_bufsize` validator [#346](amoffat/sh#346)
*   bugfix for internal stdout thread running when it shouldn't [#346](amoffat/sh#346)

*   regression bugfix on timeout [#344](amoffat/sh#344)
*   regression bugfix on `_ok_code=None`

*   further improvements on cpu usage

*   regression in cpu usage [#339](amoffat/sh#339)

*   fd leak regression and fix for flawed fd leak detection test [#337](amoffat/sh#337)

*   support for `io.StringIO` in python2

*   added support for using raw file descriptors for `_in`, `_out`, and `_err`
*   removed `.close()`ing `_out` handler if FIFO detected

*   composed commands no longer propagate `_bg`
*   better support for using `sys.stdin` and `sys.stdout` for `_in` and `_out`
*   bugfix where `which()` would not stop searching at the first valid executable found in PATH
*   added `_long_prefix` for programs whose long arguments start with something other than `--` [#278](amoffat/sh#278)
*   added `_log_msg` for advanced configuration of log message [#311](amoffat/sh#311)
*   added `sh.contrib.sudo`
*   added `_arg_preprocess` for advanced command wrapping
*   alter callable `_in` arguments to signify completion with falsy chunk
*   bugfix where pipes passed into `_out` or `_err` were not flushed on process end [#252](amoffat/sh#252)
*   deprecated `with sh.args(**kwargs)` in favor of `sh2 = sh(**kwargs)`
*   made `sh.pushd` thread safe
*   added `.kill_group()` and `.signal_group()` methods for better process control [#237](amoffat/sh#237)
*   added `new_session` special keyword argument for controlling spawned process session [#266](amoffat/sh#266)
*   bugfix better handling for EINTR on system calls [#292](amoffat/sh#292)
*   bugfix where with-contexts were not threadsafe [#247](amoffat/sh#195)
*   `_uid` new special keyword param for specifying the user id of the process [#133](amoffat/sh#133)
*   bugfix where exceptions were swallowed by processes that weren't waited on [#309](amoffat/sh#309)
*   bugfix where processes that dupd their stdout/stderr to a long running child process would cause sh to hang [#310](amoffat/sh#310)
*   improved logging output [#323](amoffat/sh#323)
*   bugfix for python3+ where binary data was passed into a process's stdin [#325](amoffat/sh#325)
*   Introduced execution contexts which allow baking of common special keyword arguments into all commands [#269](amoffat/sh#269)
*   `Command` and `which` now can take an optional `paths` parameter which specifies the search paths [#226](amoffat/sh#226)
*   `_preexec_fn` option for executing a function after the child process forks but before it execs [#260](amoffat/sh#260)
*   `_fg` reintroduced, with limited functionality.  hurrah! [#92](amoffat/sh#92)
*   bugfix where a command would block if passed a fd for stdin that wasn't yet ready to read [#253](amoffat/sh#253)
*   `_long_sep` can now take `None` which splits the long form arguments into individual arguments [#258](amoffat/sh#258)
*   making `_piped` perform "direct" piping by default (linking fds together).  this fixes memory problems [#270](amoffat/sh#270)
*   bugfix where calling `next()` on an iterable process that has raised `StopIteration`, hangs [#273](amoffat/sh#273)
*   `sh.cd` called with no arguments no changes into the user's home directory, like native `cd` [#275](amoffat/sh#275)
*   `sh.glob` removed entirely.  the rationale is correctness over hand-holding. [#279](amoffat/sh#279)
*   added `_truncate_exc`, defaulting to `True`, which tells our exceptions to truncate output.
*   bugfix for exceptions whose messages contained unicode
*   `_done` callback no longer assumes you want your command put in the background.
*   `_done` callback is now called asynchronously in a separate thread.
*   `_done` callback is called regardless of exception, which is necessary in order to release held resources, for example a process pool
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