Pretty simple.

#!/usr/bin/env bash
 
wget -S $1 2>&1 | grep -q -m 1 "Expires: Sun, 19 Nov 1978 05:00:00 GMT" \
&& echo "Yes" || echo "No"

Save the script in a file called is-drupal, and make it executable (i.e. chmod +x is-drupal) and put it in a directory in your path (e.g. ~/local/bin/). Now, you can easily check a site with following command:

is-drupal www.federicopistono.org

Found here.

I longed for this for so many year but somehow never took the effort to research it. Turns out that bash autocompletion can be be made into something sane by adding the following to profile/bashrc:

# make bash autocomplete with up arrow
bind '"\e[A":history-search-backward'
bind '"\e[B":history-search-forward'
# make tab cycle through commands instead of listing
bind '"\t":menu-complete'
# make cd try only directories
complete -d cd

From drupal4hu.