Re: Running commands as "$@"

[Davide Brini]

On Thu, 2 Feb 2023 12:11:32 +0100, Cristian Zoicas
<zoicas@medialab.sissa.it> wrote:

> Now, if a call the script with the commands
> 
>      $ sh runner.sh A=B
> 
> we get the following errors:
> 
>      runner.sh: 10: runner.sh: A=B: not found
> 
> Why the shell does not treat the first string in "$@" ('A=B'
> in these cases) as the first possibile token of command (which
> is an assignemnt)?

It works for me ("sh" points to bash).

> In addition, the problem is NOT solved by using 'eval "$@"'.
> Apparently it works. For example the command
> 
>       $ sh runner.sh A=BCD
> 
>   works, but
> 
>       $ sh runner.sh A="B    CD"
> 
> gives an error. In this case the error (I think) comes
> from the way the expansion of "$@" is performed: eval has to evaluate the
> string "A=B   CD", so it treats A=B as an assignemnt and 'CD' as
> a command.

This happens because the quotes are removed by the calling shell before eval
has a chance to see them. This works:

$ sh runner.sh 'A="B    CD"'

or even, to check

$ sh runner.sh 'A="B    CD"; echo "$A"'
B    CD

> I am curios what is going on and if there is any possibility of
> running a command (any command, including an assignment) by using
> a very simple invocation (someting like eval "$@").

The short answer is: yes, but not where quoting is involved unless you take
special measures to ensure that the relevant quotes are seen by eval.

-- 
D.