Switch ssh proxy configuration via a bash function

switch-proxy.sh

switch_proxy() {
    allowed_values=("o", "i")

    cfg_file="$HOME/.ssh/config"
    tmp_file="${cfg_file}_tmp"

    ssh_base="ssh"
    # ProxyCommand ssh -q -W %h:22 issh
    current_pattern="ProxyCommand ssh -q -W %h:22 .${ssh_base}"
    current_proxy=$(grep -e "${current_pattern}" ${cfg_file} | head -1 | tail -1 | awk '{print $NF}')
    current_proxy_symbol=$(echo ${current_proxy} | cut -c1)
    if [[ ! "${allowed_values[@]}" =~ "${current_proxy_symbol}" ]]; then
        echo "Symbol '${current_proxy_symbol}' is not allowed."
        echo "Allowed values: ${allowed_values[@]}"
        return
    fi

    if [ -n "$1" ]; then
        new_proxy_symbol="${1:0:1}"
        if [[ ! "${allowed_values[@]}" =~ "${new_proxy_symbol}" ]]; then
            echo "Symbol '${new_proxy_symbol}' is not allowed."
            echo "Allowed values: ${allowed_values[@]}"
            return
        fi
    else
        if [ "${current_proxy_symbol}" == "o" ]; then
            new_proxy_symbol="i"
        elif [ "${current_proxy_symbol}" == "i" ]; then
            new_proxy_symbol="o"
        fi
    fi

    new_proxy="${new_proxy_symbol}${ssh_base}"
    new_pattern=$(echo ${current_pattern} | sed 's/\./'"${new_proxy_symbol}"'/')

    echo "  Old proxy    : ${current_proxy}"
    echo "  New proxy    : ${new_proxy}"
    sed 's;'"$current_pattern"';'"$new_pattern"';g' ${cfg_file} > ${tmp_file}
    mv ${tmp_file} ${cfg_file}
    verify=$(grep -e "${current_pattern}" ${cfg_file} | head -1 | tail -1 | sed 's/^ *//g')
    echo "  Verification : ${verify}"
}