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Date: Sun, 25 Oct 2015 20:31:17 -0700
From: Ray Andrews <rayandrews@eastlink.ca>
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To: zsh-users@zsh.org
Subject: Re: greps pipes and eval bad patterns
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 <151025180235.ZM30558@torch.brasslantern.com>
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On 10/25/2015 06:02 PM, Bart Schaefer wrote:
> On Oct 25, 12:47pm, Ray Andrews wrote:
> }
> } test1 ()
> } {
> }      gstring=" | grep \[01;34m "
> }      tree --du -haC | grep -Ev "^[^\[]{$levels}\[*" "$gstring"
> } }
>
> One doesn't normally build up a pipeline that way, but if you must

What would be the better way?  I'm not wedded to anything, just looking 
for the
appropriate method.
>   do
> so, you're on the right track with "eval" -- you just haven't applied
> enough quoting.  "eval" is going to re-parse everything, so you need
> to quote everyhing to the same depth:
>
>      eval 'tree --du -haC | grep -Ev "^[^\[]{$levels}\[*"' "$gstring"
>
> The single quotes (before tree and after the levels pattern) keep the
> first pipeline (and importantly the double-quotes that are around the
> grep pattern) from being interpreted until eval does so.

Enlightenment.  We freeze all expansions with single quotes until eval 
sorts it all out in
one go.

> The use of
> the parameter for $gstring has the same effect.
>
> You might be able to see this better if you assign everything to
> variables before eval-ing, e.g.
>
>    test1 ()
>    {
>       gstring="| grep \[01;34m "
>       glevels='| grep -Ev "^[^\[]{$levels}\[*"'
>       tree="tree --du -haC"
>       eval "$tree" $glevels" "$gstring"

Yeah, that's the sort of thing I'm used to doing I just didn't know how 
to handle the
tricky characters.  It makes nothing but sense now that I see it. So the 
final product
becomes:

t ()
{
     local gstring=
     [ "$1" = ',f' ] && { gstring=' | grep "\[01;34m" '; shift }
     integer levels=$(( ($1 + 1) * 4 ))
     eval ' tree --du -haC | grep -Ev "^[^\[]{$levels}\[*" ' $gstring
     du -sh .
}

... a better tree than tree.