PREFIX directory for pip command

[Makoto Kuwata]

Is it possible to specify PREFIX directory for pip command by
environment variable?

I found that 'pip install --install-option=--prefix=PREFIX' works well,
but I don't want to specify '--install-option=--prefix=PREFIX' every time.
I prefer to specify it by environment variable such as::

    export PIP_INSTALL_DIR=$PWD/local

Is it possible? Or any idea?

--
regards,
makoto