sh: Add internet-check base script

Added script to sh base package to allow checking for internet
connectivity. Checks both through system virtual filesystem and, as a
fallback, through pinging google dns.

Added a simple readme to sh module.

sh/.local/bin/check-internet

@@ -0,0 +1,24 @@
+#!/usr/bin/env sh
+#
+# Check for internet connectivity.
+# Returns 0 if connectivity exists, 1 if it does not.
+
+hasconnec=0
+for intf in /sys/class/net/*; do
+    case $intf in
+    "/sys/class/net/lo") break ;;
+    *)
+        [ "$(cat "$intf/carrier")" = 1 ] && hasconnec=1
+        ;;
+    esac
+done
+
+if [ $hasconnec -ne 1 ]; then
+    ping -q -w 1 -c 1 8.8.8.8 >/dev/null 2>&1 && hasconnec=1
+fi
+
+if [ $hasconnec -eq 1 ]; then
+    exit 0
+else
+    exit 1
+fi

sh/README.md

@@ -0,0 +1,20 @@
+# sh
+
+The bare minimum terminal configuration for a working system.
+Contains:
+
+* an XDG compliant home directory setup
+* several basic environment variables
+* simple aliases
+* an optional fzf default setup
+* X autostart
+
+While other modules are largely optional, 
+this module is the only one strictly necessary for the system to really work at all.
+
+Additionally contains two scripts on which some other modules build:
+
+* a simple script to detect if applications exist
+  (and optionally warn the user if they don't)
+* and a script to check if internet connectivity exists
+