Check date of AWS token in bash

gistfile1.txt

get_token_ttl() {
    if [ -n "${AWS_CREDENTIAL_EXPIRE}" ]; then
        if date --version 2>&1 | grep -q GNU; then
            token_epoch="$(date -d "${AWS_CREDENTIAL_EXPIRE}" +%s)"
        elif date --version 2>&1 | grep -q ymwdHMS; then
            token_epoch="$(date -j -u -f '%Y-%m-%dT%H:%M:%SZ' "${AWS_CREDENTIAL_EXPIRE}" +%s)"
        fi
        current_epoch="$(date +%s)"
        echo "$(( token_epoch - current_epoch ))"
    fi
}