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Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Copy your SSH public key on a remote machine for passwordless login.
Should run on any system with ssh installed.

create random string from /dev/urandom (or another length)

Find unused IPs on a given subnet
Somewhat shorter version.

Concatenate video files to YouTube ready output
Takes two input video files and an external audio track and encodes them together to an MPEG-4 DivX output video file with the correct size ready for uploading.

Ext3 format Terabytes in Seconds

Simple XML tag extract with sed
Limited, but useful construct to extract text embedded in XML tags. This will only work if bar is all on one line. If nobody posts an alternative for the multiline sed version, I'll figure it out later...

find an unused unprivileged TCP port
Some commands (such as netcat) have a port option but how can you know which ports are unused?

(Debian/Ubuntu) Discover what package a file belongs to
Works similar to dpkg -S, but uses the locatedb and is thus inarguably a lot faster - if the locatedb is current.

Using a single sudo to run multiple && arguments
This will also work with bash instead of sh shell sudo bash -c 'apt update -y && apt upgrade -y'


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