Re: Passing variables by reference conflicts with local

[Freddy Vulto]

On 100501 12:40, Pierre Gaston wrote:
> On Sat, May 1, 2010 at 12:26 PM, Dennis Williamson wrote:
> > As Chet said, use internal variables that are unlikely to conflict.
> You can use workarounds like:
> printf -v $a "%s" foobar
> read $a <<< "%s"

The problem with obfucscated internal variables I think is that my
library code becomes unnecessary obfuscated.  That's why I'm thinking an
additional call-layer (workaround 2 in my original mail) is an
improvement in that the private library code "_blackbox()" can use
simple, readable variables without restrictions/conflicts, while the
public layer "blackbox()" checks conflicts, which - unlikely as they
might be - I'd like to return to my library users as a known error
instead of silent failing.

Revised example, replacing eval with printf -v, thanks:

    # Param: $1  variable name to return value to
    # Private library function. Do not call directly. See blackbox()
    _blackbox() {
        # Just don't declare "local __1"
        local a b c d e f g h i j
        # ...
        # Lots of complicated library code here
        # ...
        # Return value
        printf -v $1 %s b
    }

    # Param: $1  variable name to return value to
    # Public library function
    blackbox() {
        local __1
        _blackbox __1
        [[ $1 == __1 ]] && echo "ERROR: variable name conflicts"\
                "with local variable: $1"
        printf -v $1 %s "$__1"
    }

    blackbox a; echo $a           # Outputs "b" all right
    blackbox __1                  # Outputs error
    d='ls /;true'; blackbox "$d"  # No more oops


Freddy Vulto
http://fvue.nl/wiki/Bash:_passing_variables_by_reference