sshwraprc.example

#! /bin/bash
# This script defines these variable:
#   __sshwrap_config_files
#   __sshwraprc_force_update
#
# NOTE: this file is source'd so use return not exit to terminate
#       processing.

# Because we don't want the calculations here to happen for every
# ssh/scp invocation, we cache the result and use that if it exists
# and we're not on my laptop.

__sshwraprc_cache_config="$HOME/.sshwraprc.cached_config"
__sshwraprc_cache_myip="$HOME/.sshwraprc.cached_ip"
__sshwraprc_cache_extip="$HOME/.sshwraprc.cached_extip"

# if non-null then force an update to ~/.ssh/config
__sshwraprc_force_update=

myip=$(nslookup relay.known.net dns1.registrar-servers.com) ||
    errordie nslookup failed

if [[ $myip =~ Address:\ ([0-9]+\.[0-9]+\.[0-9]+\.[0-9]+) ]]; then
    myip="${BASH_REMATCH[1]}"
else
    errordie "could not parse: $myip"
fi

if [ ! "$myip" ] || 
   [ ! -f "${__sshwraprc_cache_myip}" ] ||
   [ "$myip" != "$(cat "${__sshwraprc_cache_myip}")" ]
then
    echo "[1]IP CHANGED! old: $(cat "${__sshwraprc_cache_myip}")" 1>&2
    # either the first time through this code OR
    # laptop moved from one zone to another
    echo "$myip" > "${__sshwraprc_cache_myip}"
    __sshwraprc_force_update=nonnull
fi

extip=$(my-external-ip)

if [ ! -f "${__sshwraprc_cache_extip}" ] ||
   [ "$extip" != "$(cat "${__sshwraprc_cache_extip}")" ]
then
    echo "[2]ext IP: $(cat "${__sshwraprc_cache_extip}") to $extip" 1>&2
    # our external IP changed, so force update
    echo "$extip" > "${__sshwraprc_cache_extip}"
    __sshwraprc_force_update=nonnull
fi

__sshwrap_config_files=( "$HOME/.ssh/config_top" )

if [ "$myip" = "$extip" ]; then
    __sshwrap_config_files+=( "$HOME/.ssh/config_int" )
else
    __sshwrap_config_files+=( "$HOME/.ssh/config_ext" )
fi

cat <<EOF > "${__sshwraprc_cache_config}"
__sshwrap_config_files=( ${__sshwrap_config_files[@]} )
EOF