Wait for Network Interface Before Executing Command

Question

I have a couple ideas on how I would achieve this. Not sure how I would script it.

Method 1: (probably the better choice)

Create a loop that pings a server until reply is received then execute command if no reply is received in X amount of time/runs continue script.

Method 2:

Check if network interface has valid IP then continue script

How would one go about adding this functionality in a script. Would awk or grep be of use in a situation like this? Thank you in advance for ANY input.

Answer 1

You can do the following

until ifconfig -l | grep ppp0 >/dev/null 2>&1; do :; done

Works on MacOS

Answer 2

This command should wait until it can contact google or it has tried 50 times:

for i in {1..50}; do ping -c1 www.google.com &> /dev/null && break; done

The for i in {1..50} loops 50 times or until a break is executed. The ping -c1 www.google.com sends 1 ping packet to google, and &> /dev/null redirects all the output to null, so nothing is outputed. && break executes break only if the previous command finished successfully, so the loop will end when ping is successful.