Find a public Google group for a particular host. Some of these groups contain sensitive information. The tool runs against a list of hosts and returns all public groups.

googlegroups.sh

#!/bin/bash

# Find a public Google group for a particular host. 
# Some of these groups contain sensitive information. 
# The tool runs against a list of hosts and returns all public groups.

while read domain; do
    if curl -LIs "https://groups.google.com/a/$domain" | grep "overview" > /dev/null; then
        echo "[+] https://groups.google.com/a/$domain/forum/#!overview"
    fi
done < $1

Or just use this bookmarklet to quickly check the host your are currently viewing:

javascript:window.location="https://groups.google.com/a/"+document.domain+"/forum/#!overview";

This script can run a lot faster.
Currently curl makes 3 requests per domain because of 2 redirects.

curl -LIs "https://groups.google.com/a/python.org"

HTTP/1.1 301 Moved Permanently
Content-Type: text/html; charset=UTF-8
Cache-Control: no-cache, no-store, max-age=0, must-revalidate
Pragma: no-cache
Expires: Mon, 01 Jan 1990 00:00:00 GMT
Date: Wed, 08 Jan 2020 19:55:31 GMT
Location: https://groups.google.com/a/python.org/d/
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-XSS-Protection: 1; mode=block
Server: GSE
Transfer-Encoding: chunked
Alt-Svc: quic=":443"; ma=2592000; v="46,43",h3-Q050=":443"; ma=2592000,h3-Q049=":443"; ma=2592000,h3-Q048=":443"; ma=2592000,h3-Q046=":443"; ma=2592000,h3-Q043=":443"; ma=2592000
Accept-Ranges: none
Vary: Accept-Encoding

HTTP/1.1 302 Moved Temporarily
Content-Type: text/html; charset=UTF-8
Location: /a/python.org/forum/#!overview
Date: Wed, 08 Jan 2020 19:55:32 GMT
Expires: Wed, 08 Jan 2020 19:55:32 GMT
Cache-Control: private, max-age=0
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-XSS-Protection: 1; mode=block
Server: GSE
Transfer-Encoding: chunked
Alt-Svc: quic=":443"; ma=2592000; v="46,43",h3-Q050=":443"; ma=2592000,h3-Q049=":443"; ma=2592000,h3-Q048=":443"; ma=2592000,h3-Q046=":443"; ma=2592000,h3-Q043=":443"; ma=2592000
Accept-Ranges: none
Vary: Accept-Encoding

HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Cache-Control: no-cache, no-store, max-age=0, must-revalidate
Pragma: no-cache
Expires: Mon, 01 Jan 1990 00:00:00 GMT
Date: Wed, 08 Jan 2020 19:55:33 GMT
Content-Length: 24363
P3P: CP="This is not a P3P policy! See g.co/p3phelp for more info."
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-XSS-Protection: 1; mode=block
Server: GSE
Set-Cookie: NID=195=VKxxxxxxxxxjYgTxts4; expires=Thu, 09-Jul-2020 19:55:33 GMT; path=/; domain=.google.com; HttpOnly
Alt-Svc: quic=":443"; ma=2592000; v="46,43",h3-Q050=":443"; ma=2592000,h3-Q049=":443"; ma=2592000,h3-Q048=":443"; ma=2592000,h3-Q046=":443"; ma=2592000,h3-Q043=":443"; ma=2592000

This is not necessary. You can go straight to "/a/$domain/forum/#!overview" in 1 request:
curl -Is "https://groups.google.com/a/python.org/forum/#\!overview"

HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Cache-Control: no-cache, no-store, max-age=0, must-revalidate
Pragma: no-cache
Expires: Mon, 01 Jan 1990 00:00:00 GMT
Date: Wed, 08 Jan 2020 20:00:58 GMT
Content-Length: 24363
P3P: CP="This is not a P3P policy! See g.co/p3phelp for more info."
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-XSS-Protection: 1; mode=block
Server: GSE
Set-Cookie: NID=195=kmRxxxxxxxeB0PKQGco; expires=Thu, 09-Jul-2020 20:00:58 GMT; path=/; domain=.google.com; HttpOnly
Alt-Svc: quic=":443"; ma=2592000; v="46,43",h3-Q050=":443"; ma=2592000,h3-Q049=":443"; ma=2592000,h3-Q048=":443"; ma=2592000,h3-Q046=":443"; ma=2592000,h3-Q043=":443"; ma=2592000

Without the redirects we don't even need the -L option.
How do you check if a Google Groups instance is public?
grep for the "Set-Cookie" header, instead of "overview" which appears in the "Location: " header during the redirect.

The Set-Cookie header is only present for public domains, for example:
github.com - exists, but private >> no output after grep
curl -Is "https://groups.google.com/a/github.com/forum/#\!overview" | grep "Set-Cookie"

github123.com - 404 >> no output after grep
curl -Is "https://groups.google.com/a/github123.com/forum/#\!overview" | grep "Set-Cookie"

python.com - public >> grep finds the Set-Cookie header
curl -Is "https://groups.google.com/a/python.org/forum/#\!overview" | grep "Set-Cookie"
Set-Cookie: NID=195=Xpe8xxxxxxxxxxxxxxxx9xir2CevaRUv-IpIT_4anvlJ-PUOISCeoRMJVvoRL5y1RDq8f_wEVxYhU; expires=Thu, 09-Jul-2020 20:16:05 GMT; path=/; domain=.google.com; HttpOnly

I've also changed the echoed URL to https://groups.google.com/a/$domain/forum/#!forumsearch/ so you go straight to the list of groups and don't have to click "Browse all" on the overview page.

So the final script looks something like this:

#!/bin/bash

# Find a public Google Groups for a particular host. 
# Some of these groups contain sensitive information. 
# The tool runs against a list of hosts and returns all public groups.

while read domain; do
    if curl -Is "https://groups.google.com/a/$domain/forum/#\!overview" | grep "Set-Cookie:" > /dev/null; then
        echo "https://groups.google.com/a/$domain/forum/#!forumsearch/"
    fi
done < $1

Time test on 100 domains:
Before:

time ./googlegroups.sh 100domains
./googlegroups.sh 100domains  6,17s user 1,62s system 4% cpu 2:36,17 total

After:

time ./googlegroups.sh 100domains
./googlegroups.sh 100domains  6,09s user 1,60s system 8% cpu 1:34,91 total 

2:36 > 1:34, shaved off a minute.

The results above are with 100 domains that are either private or 404. For those curl makes 2 request (1 redirect), not 3.
If you take 100 public domains, then the difference in run time is higher (3 requests / domain vs. 1 request).

Before:
./googlegroups_old.sh 100public 6,29s user 1,50s system 3% cpu 3:48,46 total

After:
./googlegroups.sh 100public 6,20s user 1,56s system 7% cpu 1:38,67 total

3:48 > 1:38
200 requests and more than 2 minutes saved, only on 100 domains.

Nice work, @milangfx! I wrote this merely as a proof of concept — not focusing on performance. If you really want performance, don't write a while loop in the script itself. Just have the script issue the requests and then run it using GNU parallel.

Thanks for the feedback. I was focusing on efficiency in a single threaded case. Making the same request run in parallel would be faster, but still inefficient.