Say when you install awscli using pip
> sudo -H pip instal --upgrade --user awscli
What happens is, pip installs the binary in
/opt/local/Library/Frameworks/Python.framework/Versions/2.7/bin/aws
and that path is not there in $PATH.
But, since /usr/local/bin is there in the PATH, we do a soft link
> cd /usr/loca/bin
> ln -s /opt/local/Library/Frameworks/Python.framework/Versions/2.7/bin/aws aws