#!/bin/bash

x=0

testfunc () {
  x=$[x+1]
  echo "testfunc: x=$x"
}

testfunc
testfunc
testfunc
echo "main/global: x=$x"


# Output:
#
# [pts/14][user@phobos]:/tmp$ ./test.sh
# testfunc: x=1
# testfunc: x=2
# testfunc: x=3
# main: x=3
# [pts/14][user@phobos]:/tmp$