Curl is great tool to do thing with HTTP in command line interface. Sometimes your want to get extra info from HTTP response and put in a variable. Here is the way :

Using --write-out is magical option help you to write out all info you want, or put it in a variable.

Example :

$ code=$(curl --write-out %{response_code} --silent --output /dev/null
$ echo $code # get http response status code
$ tracetime=$(curl --write-out "%{time_namelookup} %{time_connect} %{time_appconnect} %{time_pretransfer} %{time_redirect} %{time_starttransfer} %{time_total}" --silent --output /dev/null
$ echo $tracetime # Trace all timing of http connection (in seconds)
0.068 0.097 0.370 0.370 0.000 0.720 0.721

Use case :

Below code is cron bash script that checks if http response code equals :

  • 502 (Bad Gateway), then restart the backend server (nginx -> apache2)
  • not 200 then restart the frontend server (nginx)

code=$(curl --write-out %{response_code} --silent --output /dev/null
[ $code -eq 502 ] && sudo systemctl restart httpd || echo "everything works fine"
[ ! $code -eq 200 ] && sudo systemctl restart nginx || echo "everything works fine"

More info variables, you can check it here