On Tue, Dec 13, 2022 at 03:07:16AM -0500, Lawrence Velázquez wrote:
> Of course not. I only meant to demonstrate that "export" always
> creates global variables, so a function that utilizes "declare -gx"
> actually behaves more like "export" then your alias does.
This is a little inaccurate.
`export' doesn't always act on the *global* variable, but "declare -g"
does.
The differences are that:
* `declare' (without -g), always acts on variables in the current
dynamic scope, and will create a new variable in the current dynamic
scope if no variable with the name it was looking for exists.
* `export' and `readonly' act on the variable they can see, and set
their "x"/"r" attribute; they will only create a new variable (in the
global scope) if no variable with the name they were looking for
exists in any dynamic scope. Just like simple "a=b" assignments.
What `declare -xr' does in a function:
fun () {
declare -xr a=2
}
Is equivalent to:
fun () {
declare a=2 && # create a new "a" variable in the current scope
# and set its value to 2
export a && # set its "x" attribute
readonly a # set its "r" attribute
# when this function returns, that variable will be deleted
}
So, as we already know, a function that runs that runs only `declare'
commands (without -p, -f, or -g) is pretty much useless.
Examples:
bash-5.1$ # the `export' and `readonly' in "fun2" will act on the "a"
bash-5.1$ # variable in the dynamic scope of the "fun1" function
bash-5.1$ declare -p a
bash: declare: a: not found
bash-5.1$ fun1 () { local a=hi; fun2; declare -p a ;}
bash-5.1$ fun2 () { export a; readonly a;}
bash-5.1$ a=hello; declare -p a; fun1; declare -p a
declare -- a="hello"
declare -rx a="hi"
declare -- a="hello"
bash-5.1$ setexportreadonly () { export -- "$1" && readonly -- "$1" ;}
bash-5.1$ x=hi
bash-5.1$ declare -p x
bash-5.1$ setexportreadonly x
bash-5.1$ declare -p x
declare -rx x="hi"
bash-5.1$ # `declare -g' will bypass all the dynamic scopes, and will
bash-5.1$ # act on the global variable.
bash-5.1$ declare -p g
bash: declare: g: not found
bash-5.1$ fun1 () { local g=hi; fun2; declare -p g ;}
bash-5.1$ fun2 () { declare -grx g=hey ;}
bash-5.1$ g=hello; declare -p g; fun1; declare -p g
declare -- g="hello" # "g" in the global scope before calling fun2
declare -- g="hi" # "g" in the dynamic scope of fun1 after calling fun2
declare -rx g="hey" # "g" in the global scope after calling fun2
bash-5.1$ # `export', `readonly', and assignments in functions create
bash-5.1$ # a new global variable if there are no visible variables
bash-5.1$ # with the given name.
bash-5.1$ declare -p v{1..5}
bash: declare: v1: not found
bash: declare: v2: not found
bash: declare: v3: not found
bash: declare: v4: not found
bash: declare: v5: not found
bash: declare: v6: not found
bash-5.1$ fun1 () { local v4; fun2 "$1" ;}
bash-5.1$ fun2 () { local v5; fun3 "$1" ;}
bash-5.1$ fun3 () { local v6; eval " $1" ;}
bash-5.1$ fun1 'v1=x'; fun1 'export v2=y'; fun1 'readonly v3=z'
bash-5.1$ fun1 'v4=x'; fun1 'export v5=y'; fun1 'readonly v6=z'
bash-5.1$ declare -p v{1..5}
declare -- v1="x"
declare -x v2="y"
declare -r v3="z"
bash: declare: v4: not found
bash: declare: v5: not found
bash: declare: v6: not found
emanuele6
