initial commit

README.md

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+= Wait for it
+
+wait-for-it.sh is a pure bash script that wait on the availability of a host and TCP port.  It is useful for synchronizing the spin-up of interdependent services, such as linked docker containers.  Since it is a pure bash script, it does not have any external dependencies.
+
+For example, let's test to see if we can access port 80 on www.google.com, and if it is available, echo the message "Let's start googling!"
+
+```
+$ ./wait-for-it.sh www.google.com:80 -- echo "google is up"
+wait-for-it.sh: waiting 15 seconds for www.google.com:80
+wait-for-it.sh: www.google.com:80 is available after 0 seconds
+google is up
+```
+
+You can set your own timeout with the `-t` or `--timeout=` option.  Setting the timeout value to 0 will disable the timeout:
+
+```
+$ ./wait-for-it.sh -t 0 www.google.com:80 -- echo "google is up"
+wait-for-it.sh: waiting for www.google.com:80 without a timeout
+wait-for-it.sh: www.google.com:80 is available after 0 seconds
+google is up
+```
+
+The subcommand will be executed regardless if the service is up or not.  If you wish to only execute the subcommand only if the service is up, add the `--strict` argument. In this example, we will test port 81 on www.google.com which will fail:
+
+```
+$ ./wait-for-it.sh www.google.com:81 --timeout=1 --strict -- echo "google is up"
+wait-for-it.sh: waiting 1 seconds for www.google.com:81
+wait-for-it.sh: timeout occurred after waiting 1 seconds for www.google.com:81
+wait-for-it.sh: strict mode, refusing to execute subprocess
+```
+
+If you don't want to execute a subcommand, leave off the `--` argument.  This way, you can test the exit condition of `wait-for-it.sh` in your own scripts, and determine how to proceed:
+
+```
+$ ./wait-for-it.sh www.google.com:80
+wait-for-it.sh: waiting 15 seconds for www.google.com:80
+wait-for-it.sh: www.google.com:80 is available after 0 seconds
+$ echo $?
+0
+$ ./wait-for-it.sh www.google.com:81
+wait-for-it.sh: waiting 15 seconds for www.google.com:81
+wait-for-it.sh: timeout occurred after waiting 15 seconds for www.google.com:81
+$ echo $?
+124
+```

wait-for-it.sh

@@ -0,0 +1,156 @@
+#!/usr/bin/env bash
+#   Use this script to test if a given TCP host/port are available
+
+cmdname=$(basename $0)
+
+echoerr() { if [[ $QUIET -ne 1 ]]; then echo "$@" 1>&2; fi }
+
+usage()
+{
+    cat << USAGE >&2
+Usage:
+    $cmdname host:port [-s] [-t timeout] [-- command args]
+    -h HOST | --host=HOST       Host or IP under test
+    -p PORT | --port=PORT       TCP port under test
+                                Alternatively, you specify the host and port as host:port
+    -s | --strict               Only execute subcommand if the test succeeds
+    -q | --quiet                Don't output any status messages
+    -t TIMEOUT | --timeout=TIMEOUT
+                                Timeout in seconds, zero for no timeout
+    -- COMMAND ARGS             Execute command with args after the test finishes
+USAGE
+    exit 1
+}
+
+wait_for()
+{
+    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=$(date +%s)
+    while :
+    do
+        (echo > /dev/tcp/$HOST/$PORT) >/dev/null 2>&1
+        result=$?
+        if [[ $result -eq 0 ]]; then
+            end_ts=$(date +%s)
+            echoerr "$cmdname: $HOST:$PORT is available after $((end_ts - start_ts)) seconds"
+            break
+        fi
+        sleep 1
+    done
+    return $result
+}
+
+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 &
+    else
+        timeout $TIMEOUT $0 --child --host=$HOST --port=$PORT --timeout=$TIMEOUT &
+    fi
+    PID=$!
+    trap "kill -INT -$PID" INT
+    wait $PID
+    RESULT=$?
+    if [[ $RESULT -ne 0 ]]; then
+        echoerr "$cmdname: timeout occurred after waiting $TIMEOUT seconds for $HOST:$PORT"
+    fi
+    return $RESULT
+}
+
+# process arguments
+while [[ $# -ne 0 ]]
+do
+    case "$1" in
+        *:* ) 
+        hostport=(${1//:/ })
+        HOST=${hostport[0]}
+        PORT=${hostport[1]}
+        shift 1
+        ;;
+        --child)
+        CHILD=1
+        shift 1
+        ;;
+        -q | --quiet)
+        QUIET=1
+        shift 1
+        ;;
+        -s | --strict)
+        STRICT=1
+        shift 1
+        ;;
+        -h) 
+        HOST="$2"
+        shift 2
+        ;;
+        --host=*) 
+        HOST="${1#*=}"
+        shift 1
+        ;;
+        -p)
+        PORT="$2"
+        shift 2
+        ;;
+        --port=*)
+        PORT="${1#*=}"
+        shift 1
+        ;;
+        -t)
+        TIMEOUT="$2"
+        shift 2
+        ;;
+        --timeout=*)
+        TIMEOUT="${1#*=}"
+        shift 1
+        ;;
+        --)
+        shift
+        CLI="$@"
+        break
+        ;;
+        --help)
+        usage
+        ;;
+        *)
+        echoerr "Unknown argument: $1"
+        usage
+        ;;
+    esac
+done
+
+if [[ "$HOST" == "" || "$PORT" == "" ]]; then
+    echoerr "Error: you need to provide a host and port to test."
+    usage
+fi
+
+TIMEOUT=${TIMEOUT:-15}
+STRICT=${STRICT:-0}
+CHILD=${CHILD:-0}
+QUIET=${QUIET:-0}
+
+if [[ $CHILD -gt 0 ]]; then
+    RESULT=$(wait_for)
+    exit $RESULT
+else
+    if [[ $TIMEOUT -gt 0 ]]; then
+        wait_for_wrapper
+        RESULT=$?
+    else
+        RESULT=$(wait_for)
+    fi
+fi
+
+if [[ $CLI != "" ]]; then
+    if [[ $RESULT -ne 0 && $STRICT -eq 1 ]]; then
+        echoerr "$cmdname: strict mode, refusing to execute subprocess"
+        exit $RESULT
+    fi
+    exec $CLI
+else
+    exit $RESULT
+fi