github: add script for listing old branches

Signed-off-by: Jakub Sokołowski <jakub@status.im>

github/list_old_branches.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+function getCommitUnix() {
+    git show --no-patch --no-notes --pretty='%at' ${1}
+}
+
+OLDER_THAN_DAYS="60"
+CURRENT_TIME=$(date +%s)
+OLDER_THAN_UNIX=$(( ${OLDER_THAN_DAYS} * 86400 ))
+OLDER_THAN=$(( ${CURRENT_TIME} - ${OLDER_THAN_UNIX} ))
+
+REMOTE="origin"
+REMOTE_BRANCHES=$(git ls-remote --heads --heads ${REMOTE} | cut -f2)
+
+for BRANCH in ${REMOTE_BRANCHES}; do
+    BRANCH_NAME="${BRANCH/#refs\/heads\/}"
+    COMMIT_DATE_UNIX=$(getCommitUnix remotes/origin/$BRANCH_NAME)
+    if [[ ${COMMIT_DATE_UNIX} < ${OLDER_THAN} ]]; then
+        echo "${BRANCH_NAME}"
+    fi
+done