optimal scripts

optimal scripts

[Brendan Kehoe]

What's the fastest (most efficient) way to do something like this?

	for (foo in $bar) {
	   if ( some_test $foo ) {
		first=($first $foo);
	   } else {
		second=($second $foo);
	   }
	}

Brendan

Y-shaped pipeline

[Mark-Jason Dominus]

I have a program, `why', which expects to write output
to file descriptors 4 and 5.  

	why >[4] descriptor-four-log >[5] descriptor-five-log

works fine; the data that `why' writes to desriptor 4 winds up in
`descriptor-four-log', and the data that `why' writes to descriptor 5
goes to the file `descriptor-five-log'.

Now I want the descriptor 4 data to be piped into the stdin of some
command, say `rev', and I want the descriptor 5 data to be piped into
another command, say `cat -n'.  This doesn't work:

	why |[4] rev |[5] cat -n

because that means to connect descriptor 4 of `why' to descriptor 0 of
rev, and then to connect descriptor 5 of rev to descriptor 0 of cat -n.

How can I connect a command to two pipes at once?

Re: Y-shaped pipeline

[Chris Siebenmann]

 I thought the natural way to do it would be with '.... >[N]{command}',
but that doesn't seem to work. A pity. Anyone care to fix things so it
does?

	- cks

Re: Y-shaped pipeline

[haahr]

{ why |[4] rev } |[5] cat -n
# this does mean that the stdout of rev and cat will be intermixed
# and you should hope that rev doesn't put anything out on fd 5.