Some handy CLI tricks I use daily:

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?