Useful Linux commands

Command Description
awk '/^END/ { x = 0; } x { print $0; } /^BEGIN/ { x = 1; } ' Print text between BEGIN and END lines (exclusive).
create table t01_tmp as select distinct * from t01; drop table t01; alter table t01_tmp rename to t01; Filter duplicates from the SQLite table t01.
cut -d ',' -f 3,4 Grab columns 3 and 4 of a CSV input from stdin.
date -d@$((0x$((perl -e'print"1B","0"x95' \| xxd -r -p; sleep 1) \| nc -u time.facebook.com 123 \| tail -c+41 \| head -c4 \| xxd -p)-64#23GDW0)) Query the NTP server time.facebook.com (works on Rocky Linux’s versions of netcat / xxd).
find ~/mydir -name '*go' -exec go fmt {} \; Execute a command recursively in ~/mydir only against files with a certain file extension.
fuser -mv /mnt/disk Find all processes using the mount point /mnt/disk.
# Get most recent commit ID of Branch 2, say it's 49a8338
git fetch; git branch -v

# Switch to Branch 1
git checkout branch1

git reset --hard 49a8338
Reset Branch 1 to be identical to Branch 2 in Git.
grep -rniI ~/mydir -e 'mysearch' Search recursively in ~/mydir for the text mysearch. The -I option excludes binary files.
ls -lart Easy to remember, puts most recently changed files at the bottom of the screen.
# Run on Host 1
nc -lv 50000

# Run on Host 2
nc -v host1_hostname 50000
Checks if communication is open on port 50000 between two Linux hosts with Netcat installed.

Another option: python3 -m httpserver -p 50000 and curl host1_hostname:50000.
nslookup time.gov Does a DNS lookup of the domain time.gov against the public DNS server at Useful for comparing to nslookup time.gov, which uses its environment’s DNS configuration.
openssl s_client -connect npr.org:443 Establish a TLS connection to npr.org:443.
openssl verify -verbose -CAfile ~/cacert.pem ~/mycert.pem Determine if the CA certificate ~/cacert.pem signed the certificate ~/mycert.pem.
openssl x509 -in ~/mycert.pem -text Print the contents of the X.509 certificate ~/mycert.pem.
echo -e ".mode csv\n.import a.csv t01" \| sqlite data.sqlite3 Import the CSV file a.csv into the table t01 in the Sqlite database data.sqlite3.
ssh -N -L 50000: pi Forward local port 50000 to remote port 60000 on SSH host pi.
ssh -D 50000 -C -N pi Set up a local SOCKS listener which is tunneled to SSH host pi.
ssh-keygen -o -a 100 -t ed25519 Generate an Ed25519 SSH key.
tr -s ' ' Squeeze successive spaces to a single space.