Re: [9fans] multiple inputs

[rog@vitanuova.com]

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> fn bt {
> 	eval '{'for {tail -f $i &} '}'
> }
> 
> mimics how I would write it by hand.

if that's all you need, then

fn bt {
	for(i){tail -f $i&}
}

should be just fine.
then

	bt > file

might work (if file is append-only, otherwise you'd need a process
(e.g.  cat) in the middle to avoid overlapping writes)

using eval is disastrous...  consider what happens if you've got a
filename with a shell metacharacter in it.

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I'll agree with you there. The eval is unnecessary.

But 

fn bt {
	eval '{'for {tail -f $i &} '}'
}

mimics how I would write it by hand.

{tail -f file1 &; tail -f file2 &; tail -f file3 &}>file

Which allows me to consider the command one block, which I can pipe to and from etc.

The idiom that you and matt give doesn't work for pipes

tail -f file1 &; tail -f file2 &; tail -f file3 >file

only puts the text from file3 in the pipe. 

The for loop you gave obviates that problem, since it counts as a single block, but it's considerably different than my interactive shell usage and is more verbose(though much more readable :)).

Noah

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From: rog@vitanuova.com
To: 9fans@cse.psu.edu
Subject: Re: [9fans] multiple inputs
Date: Tue, 30 Mar 2004 17:25:46 +0100
Message-ID: <19236d27e19c4ebbe4ba92e507e29149@vitanuova.com>

> You need to put the brackets on the outside to make the combination of
> tail -f's act like a single 'tail -f'.  That was my real conceptual
> misunderstanding the first time around.

erm, i don't think so.

{a & b &}

should be exactly the same as

a & b &

you almost never need eval in rc, unless you genuinely want
to evaluate an rc expression that's unknown beforehand
(which isn't true in your case).

you could have got the behaviour i think you were after
with something like:

fn bt {
	x=$1
	shift
	for(i) {tail -f $i &}
	tail -f $x
}