Re: i dont see my code error there ...

[Alex fxmbsw7 Ratchev]

mate i visited both pages but it really doesnt tell me anything

ill read your long mail later

peeps in #bash are mommumentarly ignorant

On Thu, Mar 31, 2022 at 10:24 PM Greg Wooledge <greg@wooledge.org> wrote:

> On Thu, Mar 31, 2022 at 09:52:08PM +0200, Alex fxmbsw7 Ratchev wrote:
> > On Thu, Mar 31, 2022 at 9:42 PM Greg Wooledge <greg@wooledge.org> wrote:
> > > In fact, if the whole purpose of this exercise is to add the
> redirections
> > > when you're using time, maybe what you really want is a magic alias.
> > >
> > > unicorn:~$ t_helper() { local TIMEFORMAT=%Rs cmd; read -r _ _ cmd <
> > > <(history 1); time eval "$cmd" >/dev/null 2>&1; }
> > > unicorn:~$ alias t='t_helper # '
> > > unicorn:~$ t if sleep 1; then echo zzzz; fi
> > > 1.002s
> > >
> > > You're a big alias fan, so that should be right up your alley.  It lets
> > > you skip adding the quotes around the "argument" of t, because it's not
> > > really an argument at that point.
> > >
> > > i .. completly dont understand .. the what
> > what does history 1 there in a read
> >
> > okay now i halfway understood
> > and # is the alias'es name heh ?
>
> Magic aliases.  I'm surprised you've not run into them before, as much
> as you seem to love aliases.
> <https://www.chiark.greenend.org.uk/~sgtatham/aliases.html> is where
> I first saw them, so I'm using Simon's name for them.
>
> My variant (adapted from <https://wooledge.org/~greg/sprunge-magic-alias>)
> does its magic by turning the entire "argument" part of the user's input
> (everything after the alias's name) into a comment.  That way, it's not
> parsed at all.  The user can put anything they want.
>
> The history command is used to retrieve the user's input from the history
> buffer, so we can know what they typed.  In this case, we pass that along
> to eval.
>
> Let's simplify it slightly:
>
> unicorn:~$ helper() { local cmd; read -r _ _ cmd < <(history 1); printf
> '%s\n' "$cmd"; }
> unicorn:~$ alias x='helper # '
> unicorn:~$ x this; is; madness
> this; is; madness
>
> Here, you can see how the history command is being used.  The user types
>
> x this; is; madness
>
> And because x is an alias, this gets turned into
>
> helper # this; is; madness
>
> The helper function is called with no arguments, and it uses 'history 1'
> to figure out what the user actually typed.  The read command strips out
> the first two words (helper and #), and what's left in the cmd variable
> is everything else: "this; is; madness".  That gets sent to printf, to be
> printed.  Or in the original magic alias + helper, it gets sent to eval,
> to be parsed and executed, with time in front of it, and with redirections.
>
> As you can see, magic alias break all expectations.  When you see
>
> unicorn:~$ x this; is; madness
>
> you may think you know what's happening.  You see three simple commands
> joined by semicolons into one line.  You expect "x this" to be executed
> first, and then "is", and then "madness".
>
> But the alias changes that.  Its substitution is performed on the user's
> command before the parser even has a chance to look at the next word.
> The x is replaced by "helper #" and then the parsing is restarted.
>
>