Re: why is eval needed?

[Ray Andrews <rayandrews@eastlink.ca>]

On 2022-11-19 11:50, Lawrence Velázquez wrote:
>
> A "single argument" is not intuitive at all.  You would not run
>
>      tree '-L 2'
>
> or
>
>      tree -L\ 2
>
> so it does not make any sense to think that "tree" wants a single
> argument there.

Intuition is subjective.  Besides, usually such switches don't demand a 
space IIRC and it really is actually one argument, this is an exception. 
Even if the space is demanded, one might still think of a switch as a 
single semantic instruction even if it must be syntactically two words.  
A filename with a space in it is NOT broken in half, it's still one 
entity, so I'm thinking the same way.  I myself was naively thinking of 
it as nothing more than a string of four characters to be dropped into 
another string of characters -- as simple as that.  As if it was the 
command line. But commands do have their need to group characters into 
arguments so the invisible rules must be followed.  ' -L 2 ' must be 
invisibly broken in half.  Which, interestingly 'eval' seems to do 
automatically.  It's a huge thing coming to understand that what to me 
might look like 'just' a string of characters, to a command, needs to be 
viewed differently.  Once I understand that, things get much simpler.  I 
guess internally zsh must have all sorts of meta data attached to arrays 
to keep track of what's joined/split to/from what else.  It would be 
cool to be able to somehow see this invisible stuff, some way to see the 
invisible structure of a command line.  But I'll be ready the next time 
something like this crops up.