tee: add --write-error to control handling of closed pipes

tee is very often used with pipes and this gives better control
when writing to them.  There are 3 classes of file descriptors
that tee can write to: files(1), pipes(2), and early close pipes(3).
Handling write errors to 1 & 2 is supported at present with the caveat
that failure writing to any pipe will terminate tee immediately.
Handling write errors to type 3 is not currently supported.
To improve the supported combinations we add these options:

 --write-error=warn
   Warn if error writing any output including pipes.
   Allows continued writing to still open files/pipes.
   Exit status is failure if any output had error.
 --write-error=warn-nopipe, -p
   Warn if error writing any output except pipes.
   Allows continued writing to still open files/pipes.
   Exit status is failure if any non pipe output had error.
 --write-error=exit
   Exit if error writing any output including pipes.
 --write-error=exit-nopipe
   Exit if error writing any output except pipes.

Use the "nopipe" variants when files are of types 1 and 3, otherwise
use the standard variants with types 1 and 2.  A caveat with the above
scheme is that a combination of pipe types (2 & 3) is not supported
robustly.  I.e. if you use the "nopipe" variants when using both type
2 and 3 pipes, then any "real" errors on type 2 pipes will not be
diagnosed.
  Note also a general issue with type 3 pipes that are not on tee's
stdout, is that shell constructs don't allow to distinguish early
close from real failures.  For example `tee >(head -n1) | grep -m1 ..`
can't distinguish between an error or an early close in "head" pipe,
while the fail on the grep part of the pipe is distinguished
independently from the resulting pipe errors.  This is a general
issue with the >() construct, rather than with tee itself.

* NEWS: Mention the new feature.
* doc/coreutils.texi (tee invocation): Describe the new option.
* src/tee.c (usage): Likewise.
(main): With --write-error ignore SIGPIPE, and handle
the various exit, diagnostics combinations.
* tests/misc/tee.sh: Tess all the new options.
Fixes http://bugs.gnu.org/11540

1 files changed, 2 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 859735743..d2d8046a4 100644
--- a/NEWS
+++ b/NEWS
@@ -58,6 +58,8 @@ GNU coreutils NEWS                                    -*- outline -*-
   sync no longer ignores arguments, and syncs each specified file, or with the
   --file-system option, the file systems associated with each specified file.
 
+  tee accepts a new --write-error option to control operation with pipes.
+
 ** Changes in behavior
 
   df no longer suppresses separate exports of the same remote device, as