diff --git a/wait-for-it.sh b/wait-for-it.sh
index eca6c3b..fff13c9 100755
--- a/wait-for-it.sh
+++ b/wait-for-it.sh
@@ -1,12 +1,19 @@
-#!/usr/bin/env bash
+#!/usr/bin/env sh
 #   Use this script to test if a given TCP host/port are available
 
-cmdname=$(basename $0)
+set -e
 
-echoerr() { if [[ $QUIET -ne 1 ]]; then echo "$@" 1>&2; fi }
+cmdname=$(basename "$0")
+
+echoerr() {
+    if [ "$QUIET" -ne 1 ]; then
+        printf "%s\n" "$*" 1>&2;
+    fi
+}
 
 usage()
 {
+    exitcode="$1"
     cat << USAGE >&2
 Usage:
     $cmdname host:port [-s] [-t timeout] [-- command args]
@@ -19,22 +26,22 @@ Usage:
                                 Timeout in seconds, zero for no timeout
     -- COMMAND ARGS             Execute command with args after the test finishes
 USAGE
-    exit 1
+    exit "$exitcode"
 }
 
 wait_for()
 {
-    if [[ $TIMEOUT -gt 0 ]]; then
+    if [ "$TIMEOUT" -gt 0 ]; then
         echoerr "$cmdname: waiting $TIMEOUT seconds for $HOST:$PORT"
     else
         echoerr "$cmdname: waiting for $HOST:$PORT without a timeout"
     fi
     start_ts=$(date +%s)
-    while :
+    while true
     do
-        (echo > /dev/tcp/$HOST/$PORT) >/dev/null 2>&1
+        nc -z "$HOST" "$PORT" >/dev/null 2>&1
         result=$?
-        if [[ $result -eq 0 ]]; then
+        if [ $result -eq 0 ]; then
             end_ts=$(date +%s)
             echoerr "$cmdname: $HOST:$PORT is available after $((end_ts - start_ts)) seconds"
             break
@@ -47,29 +54,32 @@ wait_for()
 wait_for_wrapper()
 {
     # In order to support SIGINT during timeout: http://unix.stackexchange.com/a/57692
-    if [[ $QUIET -eq 1 ]]; then
-        timeout $TIMEOUT $0 --quiet --child --host=$HOST --port=$PORT --timeout=$TIMEOUT &
+    if [ "$QUIET" -eq 1 ]; then
+        timeout "$TIMEOUT" "$0" -q -child "$HOST":"$PORT" -t "$TIMEOUT" &
     else
-        timeout $TIMEOUT $0 --child --host=$HOST --port=$PORT --timeout=$TIMEOUT &
+        timeout "$TIMEOUT" "$0" --child "$HOST":"$PORT" -t "$TIMEOUT" &
     fi
     PID=$!
-    trap "kill -INT -$PID" INT
+    trap 'kill -INT -$PID' INT
     wait $PID
     RESULT=$?
-    if [[ $RESULT -ne 0 ]]; then
+    if [ $RESULT -ne 0 ]; then
         echoerr "$cmdname: timeout occurred after waiting $TIMEOUT seconds for $HOST:$PORT"
     fi
     return $RESULT
 }
 
+TIMEOUT=15
+STRICT=0
+CHILD=0
+QUIET=0
 # process arguments
-while [[ $# -gt 0 ]]
+while [ $# -gt 0 ]
 do
     case "$1" in
         *:* )
-        hostport=(${1//:/ })
-        HOST=${hostport[0]}
-        PORT=${hostport[1]}
+        HOST=$(printf "%s\n" "$1"| cut -d : -f 1)
+        PORT=$(printf "%s\n" "$1"| cut -d : -f 2)
         shift 1
         ;;
         --child)
@@ -86,16 +96,16 @@ do
         ;;
         -h)
         HOST="$2"
-        if [[ $HOST == "" ]]; then break; fi
+        if [ "$HOST" = "" ]; then break; fi
         shift 2
         ;;
         --host=*)
-        HOST="${1#*=}"
+        HOST=$(printf "%s" "$1" | cut -d = -f 2)
         shift 1
         ;;
         -p)
         PORT="$2"
-        if [[ $PORT == "" ]]; then break; fi
+        if [ "$PORT" = "" ]; then break; fi
         shift 2
         ;;
         --port=*)
@@ -104,7 +114,7 @@ do
         ;;
         -t)
         TIMEOUT="$2"
-        if [[ $TIMEOUT == "" ]]; then break; fi
+        if [ "$TIMEOUT" = "" ]; then break; fi
         shift 2
         ;;
         --timeout=*)
@@ -113,35 +123,29 @@ do
         ;;
         --)
         shift
-        CLI="$@"
         break
         ;;
         --help)
-        usage
+        usage 0
         ;;
         *)
         echoerr "Unknown argument: $1"
-        usage
+        usage 1
         ;;
     esac
 done
 
-if [[ "$HOST" == "" || "$PORT" == "" ]]; then
+if [ "$HOST" = "" -o "$PORT" = "" ]; then
     echoerr "Error: you need to provide a host and port to test."
-    usage
+    usage 2
 fi
 
-TIMEOUT=${TIMEOUT:-15}
-STRICT=${STRICT:-0}
-CHILD=${CHILD:-0}
-QUIET=${QUIET:-0}
-
-if [[ $CHILD -gt 0 ]]; then
+if [ $CHILD -gt 0 ]; then
     wait_for
     RESULT=$?
     exit $RESULT
 else
-    if [[ $TIMEOUT -gt 0 ]]; then
+    if [ "$TIMEOUT" -gt 0 ]; then
         wait_for_wrapper
         RESULT=$?
     else
@@ -150,12 +154,12 @@ else
     fi
 fi
 
-if [[ $CLI != "" ]]; then
-    if [[ $RESULT -ne 0 && $STRICT -eq 1 ]]; then
+if [ "$*" != "" ]; then
+    if [ $RESULT -ne 0 -a $STRICT -eq 1 ]; then
         echoerr "$cmdname: strict mode, refusing to execute subprocess"
         exit $RESULT
     fi
-    exec $CLI
+    exec "$@"
 else
     exit $RESULT
 fi