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Re: param expansion with single-character special vars in the environmen


From: Piotr Grzybowski
Subject: Re: param expansion with single-character special vars in the environment
Date: Wed, 27 Apr 2016 23:00:38 +0200

 wait, this one is all right, look:

1. you are making a readonly variable: readonly USER=sandbox
2. then you are creating a nameref: declare -n USER; from now on the 
assignments to USER are assignments to variable of name sandbox
3. then you create a variable sandbox and assign a value

since sandbox variable is not read only, then assignments are allowed. if you 
do readonly sandbox=someuser you will get errors all around.
 USER variable value is untouched (looking at the code); the find_varibale 
calls return the sandbox entry, as they should.

pg

On 27 Apr 2016, at 14:41, Grisha Levit wrote:

> On Wed, Apr 27, 2016 at 7:37 AM, Piotr Grzybowski <address@hidden> wrote:
> 
> 
> 
>  It seems to me that creating the reference should be allowed, but the access 
> to the referenced variable should honor its attributes.
> 
> 
> Once you convert the variable to a reference, you can control its value by 
> modifying the value of a different variable with the name that corresponds to 
> the value of the readonly variable, so “access to the referenced variable 
> should honor its attributes” probably won’t do much (If I understand your 
> suggestion correctly).
> 
> In a less convoluted example that doesn’t rely on creating our own namerefs:
> 
> readonly
>  USER=sandbox
> 
> USER=root           
> # bash: USER: readonly variable
> 
> 
> 
> declare
>  -n USER
> sandbox=root        
> # works
> 
> USER=root           
> # works
> 
> 
> [[ 
> $USER == root ]] # 0
> 
> 
> 
> # USER is unchanged, other than the -n attribute
> declare -p USER     # declare -nrx USER="sandbox"
> The above works when the readonly variable has a value that is also a valid 
> identifier. In my previous example I worked around this using the fact that 
> ref=<whatever>; declare -n ref does not check to make sure that $ref is a 
> valid identifier.
> 
> So:
> 
> readonly
>  PATH=/opt/bin
> 
> ref=
> $PATH
> declare
>  -n ref
> ref=/usr/bin
> 
> declare -p /opt/bin  # declare -- /opt/bin="/usr/bin"
> 
> 
> 
> declare -n PATH      # declare -nr PATH="/opt/bin"
> echo $PATH           # /usr/bin




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