bash: local, declare, decalre -g, readonly, export in a shell funtion.

bash_local_decalre-g_readonly_in_funtion

#!/usr/bin/env bash
# Author: Goldie Lin
# Description:
#   * "declare" in a shell function will imply "local" property.
#   * So, "declare -r" and "readonly" in a shell function are slightly different.
#   * But, "declare -gr" will be the same as "readonly".

test1() {
  declare a1="a1 is set."
  declare -r a1r="a1r is set."
}

test2() {
  readonly a2="a2 is set."
}

test3() {
  local a3="a3 is set."
  local -r a3r="a3r is set."
}

test4() {
  declare -g a4="a4 is set."
  declare -gr a4r="a4r is set."
}

test5() {
  a5="a5 is set."
  export a5e="a5e is set."
}

test1
echo "a1='${a1}'"  # a1=''
echo "a1r='${a1r}'"  # a1r=''

test2
echo "a2='${a2}'"  # a2='a2 is set.'

test3
echo "a3='${a3}'"  # a3=''
echo "a3r='${a3r}'"  # a3r=''

test4
echo "a4='${a4}'"  # a4='a4 is set.'
echo "a4r='${a4r}'"  # a4r='a4r is set.'

test5
echo "a5='${a5}'"  # a5='a5 is set.'
echo "a5e='${a5e}'"  # a5e='a5e is set.'