Re: date should become tolerant to superfluous and contradicting options

[L A Walsh]

On 2021/01/21 07:15, Adalbert Hanßen wrote:
> e.g. to/etc/bash.bashrc. However once this is done, calling
>
> date -Iminutes
>
> yields an error  because the date format is stated twice. It would be
> possible to unalias the alias by calling
>
> \date -Iminutes
>
> if one wants to let date deliver a shorter and less accurate date and
> time, but this would have to be done also in every script using date on
> that computer.
>   
Only those script that want to override local aliases.

If the script needs minutes only, then 'command date...' would work
as well, I believe what you have.  I don't see the problem.
If all scripts want to ensure they get minutes, then they
probably should either specify the overrides, specify a new alias
for date, or unalias date at the beginning of those scripts that
"care", with changes to the alias lasting the rest of the
script (+ in any children).
> Other bash commands solve this problem by letting only the last option
> prevail, if there are any contradictions because a given option
> contradicts an earlier given one.
>
> There is one more topic which I find no reference where it has  been
> addressed before: How can a script programmer guarantee that all options
> of all commands he wants to use in his script really use the default
> options he is thinking about without risking any deviations by aliases?
> Would it be an option to start a new bash in order to guarantee that?
>   
Put 'command' before things that are a command or
'function' (I think) before things that are a function,
or, if aliases are on, then 'shopt -u expand_aliases' which
would turn them off for the duration of the script (+children),
though turning off aliases won't prevent functions overriding
commands.  Actually, also, just be sure to specify the full
pathname to the executable -- that will also override alias
and function definitions.

What I tend to do (as I use aliases and functions in my shell
scripts and wouldn't want to turn them off), when I remember and
want to make sure needed files are around, is I try to setup
a function at the beginning of my scripts that, at least does
alias cmd=$(type -P cmd), but slightly better to verify scripts
fail early when lacking the utils they need.  In one such script,
I use a mkalias func for external "helper" cmnds I'll need. You
could trim this down ...  you could have extra params
in a bash hash or map array / command and run with your own
aliases in your script.

mkalias () {
 my cmd="${1:?}"         # my = alias to declare
 my path=$(type -P $cmd)
                         # die STATUS = err-func to print msg+exit w/status
 [[ $path ]] || die ENOENT "$cmd not found in path"
 if ((ifc_Debug)); then
   printf "alias %s=%s\n" "$cmd" "$path"
 fi
 alias "$cmd=$path"
}


Cheers!