Re: embraced redefinition of aliases and function causes endless recursion

[Al Elgert]

Hello

On Mon, Apr 15, 2002 at 12:17:47PM -0400, Chet Ramey wrote:
> > Machine Type: sparc-sun-solaris2.7
> > 
> > Bash Version: 2.05a
> > Patch Level: 0
> > Release Status: release
> > 
> > Description:
> >         Consider an alias is calling a function and the function
> >         calls an executable, function or bultin.
> >         (The alias is used to wrap only the interactive call of the 
> > function.)
> >         Then bash goes into endless recursion, if the alias is declared
> >         before and after the function OR the function is declared before
> >         and after the alias.
> >         A embraced redefinition always happens, if the .bashrc is
> >         sourced again.
> > 
> > Repeat-By:
> >         alias cd=cda
> >         function cda() { cd "$@"; }
> >         alias cd=cda
> >         cd /
> 
> You've created a recursive function.  Function definitions themselves are
> compound commands.  Alias expansion is performed while parsing the function

I see, that makes the difference:

        $ alias cd=cda
        $ function cda() { cd "$@"; }
        $ type cda
        cda is a function
        cda () 
        { 
            cda "$@"
        }
        $

> definition.  You end up with this function:
> 
>       function cda() { cda "$@"; }
> 
> The implications should be clear.
> 
> You can change things to do what you want by using the `builtin' command
> in the function definition.  You don't need the alias at all, in fact.
>
>       cd() { builtin cd "$@"; }

Consider the problem you want to have "another" cd in your shell functions
as in your "hand-typed-command-line" for example:

        function cd_function() {
                local fstype
                builtin cd "$@"
                fstype=$(find -maxdepth 0 -mindepth 0 -type d -printf "%F\n")
                if [ "$cd_fstype" != "$fstype" ]; then
                    echo "$cd_fstype -->> $fstype"
                fi
                cd_fstype="$fstype"
        }
        alias cd=cd_function

Now you can call cd from any function without the output from "cd_function".
But the cd from command line will notify you, if you change the filesystem.
(Well, it would be better to use "builin cd" in any function.)

> You could also quote the cd in the function definition.

Thanks, it was a little bit confusing, but now it is clear.

Alexander

-- 
Alexander Elgert
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