working with bash variables

bash_vars.sh

#!/bin/bash

my_func() {(
  # this takes a big shortcut around doing testing & unsetting -- because this entire function
  # is wrapped in "()", it executes in a subsell, so we can unconditionally unset, without
  # effecting vars outside
  unset MASTER
  echo "do something with MASTER=${MASTER-unset}"
)}

complicated_conditional_setting_and_clearing() {
  # leaving this here as an example of how to do testing for a variable to be cleared, with local vars, etc.
  # as a reference, though in this particular case the trick above is simpler
  local OLD_MASTER
  echo "MASTER=${MASTER-unset}"
  # see http://stackoverflow.com/questions/3601515/how-to-check-if-a-variable-is-set-in-bash/16753536#16753536
  if [ -n "${MASTER+x}" ]; then
    echo "clearing MASTER"
    OLD_MASTER=$MASTER
    unset MASTER
  else
    echo "MASTER not set"
  fi
  echo "do something with MASTER=${MASTER-unset}"
  if [ -n "${OLD_MASTER}" ]; then
    echo "...now resetting ..."
    MASTER=$OLD_MASTER
  else
    echo "not resetting"
  fi
}

MASTER=foo
OLD_MASTER=blah

echo "round 1"
my_func
echo "MASTER=${MASTER-unset}"
echo "OLD_MASTER=${OLD_MASTER-unset}"
echo ""


MASTER="with spaces"
echo "round 2"
my_func
echo "MASTER=${MASTER-unset}"
echo "OLD_MASTER=${OLD_MASTER-unset}"
echo ""

unset MASTER
echo "round 3"
my_func
echo "MASTER=${MASTER-unset}"
echo "OLD_MASTER=${OLD_MASTER-unset}"
echo ""

output.txt

round 1
MASTER=foo
clearing MASTER
do something with MASTER=unset
...now resetting ...
MASTER=foo
OLD_MASTER=blah

round 2
MASTER=with spaces
clearing MASTER
do something with MASTER=unset
...now resetting ...
MASTER=with spaces
OLD_MASTER=blah

round 3
MASTER=unset
MASTER not set
do something with MASTER=unset
not resetting
MASTER=unset
OLD_MASTER=blah