Change the current directory from a Bash script

You need to convert your script to a shell function:

#!/bin/bash
#
# this script should not be run directly,
# instead you need to source it from your .bashrc,
# by adding this line:
#   . ~/bin/myprog.sh
#

function myprog() {
  A=$1
  B=$2
  echo "aaa ${A} bbb ${B} ccc"
  cd /proc
}

The reason is that each process has its own current directory, and when you execute a program from the shell it is run in a new process. The standard "cd", "pushd" and "popd" are builtin to the shell interpreter so that they affect the shell process.

By making your program a shell function, you are adding your own in-process command and then any directory change gets reflected in the shell process.

When you start your script, a new process is created that only inherits your environment. When it ends, it ends. Your current environment stays as it is.

Instead, you can start your script like this:

. myscript.sh

The . will evaluate the script in the current environment, so it might be altered