bug#56025: 29.0.50; em-extpipe-test-2 times out on EMBA and Cygwin

[Jim Porter <jporterbugs@gmail.com>]

On 6/18/2022 10:52 AM, Ken Brown wrote:
> No, I'm seeing the same results on Emacs 28.  On both Emacs 28 and Emacs 
> 29, rev is apparently not seeing EOF unless echo outputs a newline, so 
> rev keeps waiting for input.

Ah ha! Thanks for debugging this. The minimal fix then would be to 
change the command in em-extpipe-test-2 to either of these:

   echo -N "bar" | rev *>temp
   *echo "bar" | rev *>temp

One last[1] question: if you ran "echo -n bar | rev" in Cygwin Bash, 
does it hang there too? Maybe this is just a Cygwin limitation, or maybe 
Eshell is doing something wrong with its built-in pipelines in this 
situation.

> [Side note: It took me a while to sort this out because (a) Eshell's 
> echo does not output a newline by default, in contrast to Bash's builtin 
> echo; (b) in Eshell in Emacs 28, you use '-n' to add a newline, while in 
> Bash '-n' suppresses the newline; and (c) in Eshell in Emacs 29, you use 
> '-N' to add a newline.]

This is one of the parts of Eshell that's always bothered me a bit. 
Eshell's echo is different enough from other echo implementations that 
it's easy to get tripped up. There's some further discussion of this in 
bug#12689 as well. I'm hesitant to change Eshell's echo too much, since 
it could break user scripts, but it would be nice if we could find a 
reasonably-compatible way of making it work more like /bin/echo.

[1] Well, probably last.