.git/hooks/post-checkout for logging branch changes. Will mine this to see what sort of frecency map would be useful for finding "hot" branches

post-checkout

#!/bin/sh

previous_head_ref=$1
new_head_ref=$2
is_branch_checkout=$3

if [[ "$previous_head_ref" != "$new_head_ref" ]] && [[ "$is_branch_checkout" == 1 ]]; then
    branch=$(git rev-parse --abbrev-ref HEAD)
    #if [[ "develop" != "$branch" ]]; then
        path="$(dirname "$0")/.."
        logfile="$path/x_branch_log"
        ts=$(date +%s)
        echo "$branch|1|$ts" >> $logfile
    #fi
fi

post-checkout hook provides the raw SHA1 for previous_head and current_head. At first I tried to turn those back into branch names, but that was error-prone (could be the tip of multiple branches). But then realized I could get the branch info from the new branch via rev-parse, since post-checkout runs after the checkout is complete (by definition).

git rev-parse --abbrev-ref HEAD is the preferred way to get the current branch using git plumbing.