There isn't a built-in flag yet, but you can use

pip freeze --local | grep -v '^-e' | cut -d = -f 1 | xargs -n1 pip install -U

Note: there are infinite potential variations for this. I'm trying to keep this answer short and simple, but please do suggest variations in the comments!

Relevant edits:

Added a grep to skip "-e" package definitions, as suggested by @jawache (Yes, you could replace grep+cut with sed or awk or perl or...).

Newer versions of pip allow you to list outdated packages:

pip list --outdated --format=freeze

Added -n1 to xargs, prevents stopping everything if updating one package fails (thanks @andsens)

source : https://stackoverflow.com/questions/2720014/upgrading-all-packages-with-pip#3452888