Add shellcheck and some integration tests

And fix the Errors that shellcheck found.

runs curl | bash installer on a handful of
containers for distros that we support.
The fedora/redhat type distros don't put
systemd in their containers, or the containers
otherwise don't work the way we expect the real os to,
so they aren't in the test matrix.

.github/workflows/ci.yml

@@ -0,0 +1,43 @@
+name: Curl | Bash Test
+on:
+  push:
+    paths:
+      - install.sh.in
+      - .github/workflows/ci.yml
+    # branches: [ main ]
+  schedule:
+    - cron: "0 0 * * 0"   # weekly
+jobs:
+  shellcheck:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository code
+        uses: actions/checkout@v4
+      - run: sudo apt install -y shellcheck
+      - run: shellcheck -S error install.sh.in
+
+  curl-bash:
+    needs: shellcheck
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        container:
+          - "ubuntu:latest"
+          - "ubuntu:24.10"
+          - "ubuntu:24.04"
+          - "ubuntu:22.04"
+          - "ubuntu:20.04"
+          - "debian:latest"
+          - "debian:12"
+          - "debian:11"
+          - "debian:10"
+          - "kalilinux/kali-rolling:latest"
+
+    container:
+      image: ${{ matrix.container }}
+
+    steps:
+      - name: apt
+        run: apt-get -y update && apt-get -y install curl gnupg2 gnupg gpg || true
+      - name: install ${{ matrix.container }}
+        run: curl -s https://install.zerotier.com | bash

install.sh.in

@@ -1,3 +1,4 @@
+# shellcheck disable=SC2148
 ENDOFSIGSTART=
 
 export PATH=/bin:/usr/bin:/usr/local/bin:/sbin:/usr/sbin:/usr/local/sbin
@@ -230,21 +231,21 @@ write_apt_repo() {
 	$SUDO apt-get install -y gpg
 	$SUDO chmod a+r /tmp/zt-gpg-key
 
-	if   [[ "$DISTRIBUTION" == "ubuntu" && "$VERSION" < "22.04" ]]; then
+	if   [[ "$DISTRIBUTION" == "ubuntu" && $(echo "$VERSION < 22.04" | bc) ]]; then
 		_old_apt_signing $URL $CODENAME
-	elif [[ ("$DISTRIBUTION" == "debian" || "$DISTRIBUTION" == "raspbian") && "$VERSION" -lt "10" ]]; then
+	elif [[ ("$DISTRIBUTION" == "debian" || "$DISTRIBUTION" == "raspbian") && $(echo "$VERSION < 10" | bc ) ]]; then
 		_old_apt_signing $URL $CODENAME
-	elif [[ "$DISTRIBUTION" == "ubuntu" && "$VERSION" > "22.03" ]]; then  # comparison to 22.03 is intentional
+	elif [[ "$DISTRIBUTION" == "ubuntu" && $(echo "$VERSION > 22.03" | bc) ]]; then  # comparison to 22.03 is intentional
 		_new_apt_signing $URL $CODENAME
-	elif [[ ("$DISTRIBUTION" == "debian" || "$DISTRIBUTION" == "raspbian") && "$VERSION" -ge "10" ]]; then
+	elif [[ ("$DISTRIBUTION" == "debian" || "$DISTRIBUTION" == "raspbian") && $(echo "$VERSION >= 10" | bc) ]]; then
 		_new_apt_signing $URL $CODENAME
 	elif [[ "$DISTRIBUTION" == "kali" ]]; then
 		_new_apt_signing $URL $CODENAME
 	elif [[ "$DISTRIBUTION" == "linuxmint" && "$VERSION" == "6" ]]; then
 		_new_apt_signing $URL $CODENAME
-	elif [[ "$DISTRIBUTION" == "linuxmint" && ( "$VERSION" == "21" || "$VERSION" > "21" ) ]]; then
+	elif [[ "$DISTRIBUTION" == "linuxmint" && ( "$VERSION" == "21" || $(echo "$VERSION > 21" | bc) ) ]]; then
 		_new_apt_signing $URL $CODENAME
-	elif [[ "$DISTRIBUTION" == "linuxmint" && ( "$VERSION" == "20" || ("$VERSION" > "20" && "$VERSION" < "21" ) ) ]]; then
+	elif [[ "$DISTRIBUTION" == "linuxmint" && ( "$VERSION" == "20" || ( $(echo "$VERSION > 20" | bc) && $(echo "$VERSION < 21" | bc ) ) ) ]]; then
 		_old_apt_signing $URL $CODENAME
 	else
 		echo "Unsupported distribution $DISTRIBUTION $VERSION"
@@ -296,7 +297,7 @@ elif [ $ID == "ubuntu" ] || [ $ID == "pop" ]; then
 elif [ $ID == "linuxmint" ]; then
 	echo '*** Detected Linux Mint, creating /etc/apt/sources.list.d/zerotier.list'
 
-	if [[ "$VERSION_ID" > "$MAX_SUPPORTED_MINT_VERSION" ]]; then
+	if [[ "$VERSION_ID" -gt "$MAX_SUPPORTED_MINT_VERSION" ]]; then
 		write_apt_repo $ID $MAX_SUPPORTED_MINT_VERSION $ZT_BASE_URL_HTTP $MAX_SUPPORTED_MINT_VERSION_NAME
 	else 
 		write_apt_repo $ID $VERSION_ID $ZT_BASE_URL_HTTP ${MINT_CODENAME_MAP[${VERSION_CODENAME}]}