Passing array to function

Passing array to function

[Ignatius Reilly]

I have the following function:

addtoarray() { [[ -d $1 ]] && myarray=($1 $myarray) }

which works as expected, prepending an element to an array only if its an
existing directory.  I'd like to rewrite this function so that I can pass
the array name as a parameter like so:

addtoarray /usr/foo myarray

but I can't figure out how.  I've tried everything I can think of without
any success.

Thanks

Re: Passing array to function

[Daniel Shahaf]

Ignatius Reilly wrote on Fri, Sep 30, 2016 at 02:15:55 -0500:
> addtoarray() { [[ -d $1 ]] && myarray=($1 $myarray) }
> 
> which works as expected, prepending an element to an array only if its an
> existing directory.  I'd like to rewrite this function so that I can pass
> the array name as a parameter like so:
> 
> addtoarray /usr/foo myarray

You could do it with eval:

addtoarray() {
  [[ -d $1 ]] && eval "${(q)2}[1,0]=${(q)1}"
}

Explanation:

- The (q) are there to convert the values to command-line-quoted
  strings, for eval.  $2 probably needs no quoting — if it did, the eval
  would see a syntax error — but I put the (q) anyway to guard against
  invalid inputs (bobby tables attacks against the eval).

- After parameter substitution, the resultant string is:
    myarray[1,0]=/usr/foo
  which is a slice assignment that prepends an element to the named
  array.

If there's a solution without eval I'm sure someone will post it.

Cheers,

Daniel


> Thanks
> 

Re: Passing array to function

[Mikael Magnusson]

On Fri, Sep 30, 2016 at 9:45 AM, Daniel Shahaf <d.s@daniel.shahaf.name> wrote:
> Ignatius Reilly wrote on Fri, Sep 30, 2016 at 02:15:55 -0500:
>> addtoarray() { [[ -d $1 ]] && myarray=($1 $myarray) }
>>
>> which works as expected, prepending an element to an array only if its an
>> existing directory.  I'd like to rewrite this function so that I can pass
>> the array name as a parameter like so:
>>
>> addtoarray /usr/foo myarray
>
> You could do it with eval:
>
> addtoarray() {
>   [[ -d $1 ]] && eval "${(q)2}[1,0]=${(q)1}"
> }
>
> Explanation:
>
> - The (q) are there to convert the values to command-line-quoted
>   strings, for eval.  $2 probably needs no quoting — if it did, the eval
>   would see a syntax error — but I put the (q) anyway to guard against
>   invalid inputs (bobby tables attacks against the eval).
>
> - After parameter substitution, the resultant string is:
>     myarray[1,0]=/usr/foo
>   which is a slice assignment that prepends an element to the named
>   array.
>
> If there's a solution without eval I'm sure someone will post it.

addtoarray() { [[ -d $1 ]] || return; local p="$2[1,0]"; : ${(P)p::=$1} }
I forgot about [1,0] yesterday when you asked on IRC.

-- 
Mikael Magnusson

Re: Passing array to function

[Bart Schaefer]

On Sep 30,  7:45am, Daniel Shahaf wrote:
} Subject: Re: Passing array to function
}
} Ignatius Reilly wrote on Fri, Sep 30, 2016 at 02:15:55 -0500:
} > addtoarray() { [[ -d $1 ]] && myarray=($1 $myarray) }
} > 
} > addtoarray /usr/foo myarray
} 
} addtoarray() {
}   [[ -d $1 ]] && eval "${(q)2}[1,0]=${(q)1}"
} }

Solution without eval:

    addtoarray() { [[ -d $1 ]] && set -A $2 $1 ${(P)2}  }

Various quoting may be necessary if you using an emulation mode or
other nonstandard setopts, but from your original example it does
not appear so.  ${(P)2} means to treat the value of $2 as a name
and expand that named parameter.