Re: piping surprise

[Bart Schaefer <schaefer@brasslantern.com>]

On Wed, Apr 3, 2024 at 11:49 AM Ray Andrews <rayandrews@eastlink.ca> wrote:
>
> I believe Bart had a solution to that.

I can't think what you're referring to, but in the realm of the baroque ...

typeset -gi Pnum
alias -g '|'='> ${TMPPREFIX}pipe$$.$((++Pnum)) ; < ${TMPPREFIX}pipe$$.$((Pnum))'

This uses global aliasing to replace the '|' token with I/O
redirection through a (relatively) uniquely named temporary file.
Only works if the left side actually finishes writing so that the
right side can start reading.

However, there's a bug (?) in that if you chain together several
commands this way, only the first $((++Pnum)) actually increments the
parameter, so all the commands end up with the same file names.  E.g.

echo foo | tr a-z A-Z | cat

just prints "foo".  You can see this by writing it all out and
inserting an extra "echo":

echo PIPE > pipe.$((++Pnum)); echo $Pnum;\
 < pipe.$((Pnum)) cat > pipe.$((++Pnum)); echo $Pnum ; < pipe.$((Pnum)) cat

This will echo the same number twice, where it should echo consecutive
numbers.  This only happens if the autoincrement appears in a
redirection.