Simple clean environment

conf.sh

# Example configuration

export PATH=/usr/bin

export FOO=1
export BAR=2

stage1.sh

#!/bin/bash

# Run next stage in empty environment
/usr/bin/env -i /bin/bash stage2.sh $1

stage2.sh

# Populate env with configuration
source $1

# Next stage
/bin/bash stage3.sh

stage3.sh

# Example last stage:

echo $FOO $BAR