Check certificate details

Show cert expiry and subject for a live TLS endpoint

openssl s_client -connect example.com:443 </dev/null 2>/dev/null | openssl x509 -noout -dates -subject

More linux commands

Awk — sum a column

awk '{sum += $3} END {print sum}' file.txt

Sum the 3rd column of a space-delimited text file
Sed — replace in file

sed -i 's/old-string/new-string/g' file.txt

In-place global string replacement
Sort and deduplicate

sort file.txt | uniq -c | sort -rn | head -20

Count and rank duplicate lines in a file
List block devices

lsblk -o NAME,SIZE,TYPE,FSTYPE,MOUNTPOINT,UUID

Tree of disks, partitions, loop devices with filesystem info
Show block device UUIDs

blkid

Print UUID, LABEL, and FSTYPE for all block devices