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116 lines
3.1 KiB
Bash
116 lines
3.1 KiB
Bash
#!/usr/bin/env sh
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# shellcheck shell=dash
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#/ Use DNS to find out about the external IP of the running system.
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#/
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#/ This script is useful when running from a machine that sits behind a NAT.
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#/ Due to how NAT works, machines behind it belong to an internal or private
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#/ subnet, with a different address space than the external or public side.
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#/
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#/ Typically it is possible to make an HTTP request to a number of providers
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#/ that offer the external IP in their response body (eg: ifconfig.me). However,
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#/ why do a slow and heavy HTTP request, when DNS exists and is much faster?
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#/ Well established providers such as OpenDNS or Google offer special hostnames
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#/ that, when resolved, will actually return the IP address of the caller.
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#/
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#/ https://unix.stackexchange.com/questions/22615/how-can-i-get-my-external-ip-address-in-a-shell-script/81699#81699
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#/
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#/
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#/ Arguments
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#/ ---------
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#/
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#/ --ipv4
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#/
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#/ Find the external IPv4 address.
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#/ Optional. Default: Enabled.
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#/
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#/ --ipv6
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#/
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#/ Find the external IPv6 address.
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#/ Optional. Default: Disabled.
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# Shell setup
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# ===========
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# Shell options for strict error checking.
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for OPTION in errexit errtrace pipefail nounset; do
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set -o | grep -wq "$OPTION" && set -o "$OPTION"
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done
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# Trace all commands (to stderr).
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#set -o xtrace
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# Shortcut: REAL_EXTERNAL_IP
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# ==========================
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if [ -n "${REAL_EXTERNAL_IP:-}" ]; then
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echo "$REAL_EXTERNAL_IP"
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exit 0
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fi
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# Parse call arguments
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# ====================
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CFG_IPV4="true"
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while [ $# -gt 0 ]; do
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case "${1-}" in
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--ipv4) CFG_IPV4="true" ;;
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--ipv6) CFG_IPV4="false" ;;
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*)
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echo "Invalid argument: '${1-}'" >&2
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exit 1
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;;
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esac
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shift
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done
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# Discover the external IP address
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# ================================
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if [ "$CFG_IPV4" = "true" ]; then
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COMMANDS='dig @resolver1.opendns.com myip.opendns.com A -4 +short
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dig @ns1.google.com o-o.myaddr.l.google.com TXT -4 +short | tr -d \"
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dig @1.1.1.1 whoami.cloudflare TXT CH -4 +short | tr -d \"
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dig @ns1-1.akamaitech.net whoami.akamai.net A -4 +short'
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is_valid_ip() {
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# Check if the input looks like an IPv4 address.
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# Doesn't check if the actual values are valid; assumes they are.
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echo "$1" | grep -Eq '^([0-9]{1,3}\.){3}[0-9]{1,3}$'
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}
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else
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COMMANDS='dig @resolver1.opendns.com myip.opendns.com AAAA -6 +short
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dig @ns1.google.com o-o.myaddr.l.google.com TXT -6 +short | tr -d \"
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dig @2606:4700:4700::1111 whoami.cloudflare TXT CH -6 +short | tr -d \"'
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is_valid_ip() {
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# Check if the input looks like an IPv6 address.
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# It's almost impossible to check the IPv6 representation because it
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# varies wildly, so just check that there are at least 2 colons.
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[ "$(echo "$1" | awk -F':' '{print NF-1}')" -ge 2 ]
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}
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fi
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echo "$COMMANDS" | while read -r COMMAND; do
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if IP="$(eval "$COMMAND")" && is_valid_ip "$IP"; then
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echo "$IP"
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exit 100 # Exits the pipe subshell.
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fi
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done
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if [ $? -eq 100 ]; then
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exit 0
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else
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echo "[$0] All providers failed" >&2
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exit 1
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fi
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