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43527, tweaked: describe which output behaviour in FAQ.

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Peter Stephenson 2018-09-24 14:34:31 +01:00
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@ -1,3 +1,8 @@
2018-09-24 Peter Stephenson <p.stephenson@samsung.com>
* 43527, tweaked: Etc/FAQ.yo: describe "which" output
behaviour.
2018-09-23 Oliver Kiddle <okiddle@yahoo.co.uk> 2018-09-23 Oliver Kiddle <okiddle@yahoo.co.uk>
* gitlab !2: Noam Barnea: Completion/Unix/Command/_toilet: * gitlab !2: Noam Barnea: Completion/Unix/Command/_toilet:

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Etc/FAQ.yo
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@ -127,6 +127,7 @@ Chapter 3: How to get various things to work
3.26. Why is my output duplicated with `tt(foo 2>&1 >foo.out | bar)'? 3.26. Why is my output duplicated with `tt(foo 2>&1 >foo.out | bar)'?
3.27. What are these `^' and `~' pattern characters, anyway? 3.27. What are these `^' and `~' pattern characters, anyway?
3.28. How do I edit the input buffer in $EDITOR? 3.28. How do I edit the input buffer in $EDITOR?
3.29. Why does `which' output for missing commands go to stdout?
Chapter 4: The mysteries of completion Chapter 4: The mysteries of completion
4.1. What is completion? 4.1. What is completion?
@ -1964,6 +1965,34 @@ label(328)
quitting the editor will only return to zsh's command-line editing mode. quitting the editor will only return to zsh's command-line editing mode.
sect(Why does `which' output for missing commands go to stdout?)
The issue is that if you run:
verb(
which non-existent-command
)
the error message goes, unusually, to standard output rather than
to standard error. Other shells send this message to standard error,
as they would if the command was about to be executed but could not be
found.
The original reason for this is that this behaviour is inherited
from the C shell (csh), where `tt(which)' itself originated. So
it has been in zsh a very long time, and it is now a feature.
(It would be possible to change this in emulation modes; however.
so far this possibility has been seen has more of an additional
confusion than a help.)
If you want some further rationalisation, which may be what the C
shell designers had in mind, you might note that `tt(which)' is
designed as a way of outputting information about a command. So
`this command can be found in ...' and `this command can't be found'
are both bits of information here, unlike the case where the command
is to be executed. So although it differs from other Bourne-style
shells it is in fact self-consistent. Note that the exit status does
reflect the fact the command can't be found.
chapter(The mysteries of completion) chapter(The mysteries of completion)