I'll provide this commandline with the terms that I am not responsible for any screw-ups due to it. (caveat: if your local repo specifies to merge, it will attempt merge or maybe warn.)
Find all your .gits and
git pull each project:
find ~/ -type d -name ".git" -exec git -C '{}/..' pull \;
If you prefer to actually see which are updating, try:
find ~/ -type d -name ".git" -exec echo "{}" \; -exec git -C '{}/..' pull \; -exec echo "" \;
good luck!
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