result.txt

taniguchi.takanori@O-13660-MAC:/tmp[3057]% cat a.sh     
#!/bin/bash

function hoge(){
    local i
    i="I am local"
    g="I am global"
}

taniguchi.takanori@O-13660-MAC:/tmp[3058]% cat b.sh 
#!/bin/bash

i="who am i?"
g=$i

echo "i: $i"
echo "g: $g"

echo "use . a.sh"
. a.sh
hoge
echo "i: $i"
echo "g: $g"

: -----
i="who am i?"
g=$i

echo "use source a.sh"
source a.sh
hoge

echo "i: $i"
echo "g: $g"
taniguchi.takanori@O-13660-MAC:/tmp[3059]% ./b.sh 
i: who am i?
g: who am i?
use . a.sh
i: who am i?
g: I am global
use source a.sh
i: who am i?
g: I am global
taniguchi.takanori@O-13660-MAC:/tmp[3060]% sw_vers
ProductName:    macOS
ProductVersion: 11.5
BuildVersion:   20G71
taniguchi.takanori@O-13660-MAC:/tmp[3061]% bash --version
GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin20)
Copyright (C) 2007 Free Software Foundation, Inc.
taniguchi.takanori@O-13660-MAC:/tmp[3062]%