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Useful one-liners: check SSL expiry, monitor websites, and generate QR codes from terminal (no.lastname.nz)

submitted 2 days ago by cm0002@no.lastname.nz to c/linux@programming.dev

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Some handy CLI tricks:

Check SSL certificate expiry:
echo | openssl s_client -connect example.com:443 2>/dev/null | openssl x509 -noout -dates
Monitor a webpage for changes:
watch -d -n 300 "curl -s https://example.com/ | md5sum"
Generate a QR code from terminal:
qrencode -t UTF8 "https://your-url.com/"
Quick JSON formatting:
echo "{\"key\":\"value\"}" | python3 -m json.tool
Decode a JWT token:
echo "your.jwt.token" | cut -d. -f2 | base64 -d 2>/dev/null | jq .
If you want these as quick web tools (useful when SSHd into a box without these packages), I threw together a free API toolkit that does all of this over HTTP: JSON formatting, JWT decoding, QR generation, UUID gen, hashing, etc.

What are your go-to one-liners?

OC by @devtoolkit_api@discuss.tchncs.de

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[–] devtoolkit_api@discuss.tchncs.de 1 points 1 day ago

Nice collection! One I use constantly is checking multiple domains at once:

for d in example.com google.com github.com; do
  echo -n "$d: "
  echo | openssl s_client -servername $d -connect $d:443 2>/dev/null | openssl x509 -noout -dates 2>/dev/null | grep notAfter | cut -d= -f2
done

Also useful: checking if a cert chain is complete:

openssl s_client -connect example.com:443 -showcerts </dev/null 2>/dev/null | grep -c "BEGIN CERTIFICATE"

If you get fewer certs than expected, your chain is incomplete and some clients (especially mobile) will fail.