A shellscript which hangs for up to 30 seconds while waiting for a port to become accessible.

usage.md

A simple way to test this is to run wait_for_port.sh against localhost on a random unused port:

$ .ci/wait_for_port.sh localhost 12345
.....

Then in another shell, listen on that port:

$ nc -l 12345

... and watch how wait_for_port.sh exits beautifully in the first shell:

$ .ci/wait_for_port.sh localhost 12345
................Connection to localhost port 12345 [tcp/italk] succeeded!
OK

This can be quite handy for example when orchestrating CI :-)

wait_for_port.sh

#!/bin/bash
RETRIES=30
SUCCESS=1
TRY=0

HOST=$1
PORT=$2

if [ -z "$HOST" -o -z "$PORT" ]
then
    echo "Usage: wait_for_port.sh <host> <port>"
    exit 1
fi

while [ $SUCCESS -eq 1 -a $TRY -le $RETRIES ]
do
    nc -z -w 1 $HOST $PORT 2>&1 > /dev/null

    let SUCCESS=$?
    if [ $SUCCESS -eq 0 ]
    then
        echo OK
        exit 0
    else
        let TRY=$TRY+1
        sleep 1
    fi
    printf '.'
done

echo Failure in $RETRIES tries
exit 1