Source: just-shadow@stackoverflow
Test before
git branch | grep "StringToFind" | awk '{original=$1; sub("StringToFind","ReplaceWith"); print original, "->" , $1}'
Rename
git branch | grep "StringToFind" | awk '{original=$1; sub("StringToFind","ReplaceWith"); print original, $1}' | xargs -n 2 git branch -M