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Simple server which listens on a port and prints out received data
Sometimes you need a simple server which listens on a port and prints out received data. Example: Consider you want to know, which data is posted by a homepage to a remote script without analysing the html code! A simple way to do this is to save the page to your computer, substitude all action="address" with action="localhost:portnumber", run 'ncat -l portnumber' and open the edited page with your browser. If you then submit the form, ncat will print out the http-protocol with all the posted data.

Clone IDE Hard Disk
This command clone the first partition of the primary master IDE drive to the second partition of the primary slave IDE drive (!!! back up all data before trying anything like this !!!)

Watch command
Repeat command after every 2 secs

Limit the transfer rate and size of data over a pipe
This example will close the pipe after transferring 100MB at a speed of 3MB per second.

copy timestamps of files from one location to another - useful when file contents are already synced but timestamps are wrong.
Sometimes when copying files from one place to another, the timestamps get lost. Maybe you forgot to add a flag to preserve timestamps in your copy command. You're sure the files are exactly the same in both locations, but the timestamps of the files in the new home are wrong and you need them to match the source. Using this command, you will get a shell script (/tmp/retime.sh) than you can move to the new location and just execute - it will change the timestamps on all the files and directories to their previous values. Make sure you're in the right directory when you launch it, otherwise all the touch commands will create new zero-length files with those names. Since find's output includes "." it will also change the timestamp of the current directory. Ideally rsync would be the way to handle this - since it only sends changes by default, there would be relatively little network traffic resulting. But rsync has to read the entire file contents on both sides to be sure no bytes have changed, potentially causing a huge amount of local disk I/O on each side. This could be a problem if your files are large. My approach avoids all the comparison I/O. I've seen comments that rsync with the "--size-only" and "--times" options should do this also, but it didn't seem to do what I wanted in my test. With my approach you can review/edit the output commands before running them, so you can tell exactly what will happen. The "tee" command both displays the output on the screen for your review, AND saves it to the file /tmp/retime.sh. Credit: got this idea from Stone's answer at http://serverfault.com/questions/344731/rsync-copying-over-timestamps-only?rq=1, and combined it into one line.

Broadcast your shell thru UDP on port 5000
Better solution in case of many clients, imo.

Generate a list of installed packages on Debian-based systems

Annotate tail -f with timestamps
Uses the command ts in order to add a timestamp on each line. This command is provided in the moreutils package on Debian, and you may need libtime-duration-perl to be able to format the date.

use wget to check if a remote file exists

send a circular


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