Am 17.05.2016 um 19:39 schrieb Alain:

> 
>>
>> Like Kenneth, I have never been aware of that either! It won't change my
>> habit though ;-)
>>
>> The use of "|" in e.g. #if (x>10 | z<=20) is legitimate though? What
>> other, invalid, use are you talking of?
>>
>>
> 
> dir |more
> 
> This induce a pose after each creen full with the display of [more] on
> the last line. Press any key, the [more] goes away, and you get the next
> screen full.
> 
> "dir /w |more" will display on 5 column and pose after a screen full.
> I think that "dir |more /w" will causse an error or ignore the /w option.

The "|more" is not actually an option to the "dir" command; instead, the
pipe symbol adds an /output filter/ to the command, which takes the
output of the primary command (in this case "dir") and does some magic
tricks with it (in this case, "more", waiting for a key press every X
lines). In that sense, it is pretty similar (and, as far as the syntax
is concerned, identical) to the Unix command shell's concept of a "pipe"
(feeding a program's textual output to another program as textual
input), though IIRC in DOS there were some serious limitations regarding
the choice of programs you could use as an output filter (in DOS, for
instance, I'd guess the filter program had to be a .com rather than an
.exe), and I'm also not sure whether DOS supported the chaining of
multiple such filters.

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