Improve handling of interface waiting with single argument

The previous code wasn't using $# to count the number of arguments, which
triggered the interface waiting code for any number of arguments.

The interface waiting code is not run if the single parameter is the name
of a file found in $PATH.

Minor code cleanup.

Author: robinsmidsrod

util/entrypoint.sh

@@ -1,16 +1,23 @@
 #!/bin/bash
+
 set -e
 
+
+init="/usr/bin/dumb-init"
+
 # Single argument to command line is interface name
-if [ -n "$1" ]; then
-    # loop until interface is found, or we give up
-    NEXT_WAIT_TIME=1
-    until [ -e "/sys/class/net/$1" ] || [ $NEXT_WAIT_TIME -eq 4 ]; do
-        sleep $(( NEXT_WAIT_TIME++ ))
-        echo "Waiting for $1 to become available.... ${NEXT_WAIT_TIME}"
-    done
-    if [ -e "/sys/class/net/$1" ]; then
-        IFACE=$1
+if [ $# -eq 1 -a -n "$1" ]; then
+    # skip wait-for-interface behavior if found in path
+    if ! which "$1" >/dev/null; then
+        # loop until interface is found, or we give up
+        NEXT_WAIT_TIME=1
+        until [ -e "/sys/class/net/$1" ] || [ $NEXT_WAIT_TIME -eq 4 ]; do
+            sleep $(( NEXT_WAIT_TIME++ ))
+            echo "Waiting for interface '$1' to become available... ${NEXT_WAIT_TIME}"
+        done
+        if [ -e "/sys/class/net/$1" ]; then
+            IFACE="$1"
+        fi
     fi
 fi
 
@@ -19,8 +26,6 @@ if [ -z "$1" ]; then
     IFACE=" "
 fi
 
-init="/usr/bin/dumb-init"
-
 if [ -n "$IFACE" ]; then
     # Run dhcpd for specified interface or all interfaces