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Randomize lines in a file
Works in sort (GNU coreutils) 7.4, don't know when it was implemented but sometime the last 6 years.

Read and write to TCP or UDP sockets with common bash tools
Ever needed to test firewalls but didn't have netcat, telnet or even FTP? Enter /dev/tcp, your new best friend. /dev/tcp/(hostname)/(port) is a bash builtin that bash can use to open connections to TCP and UDP ports. This one-liner opens a connection on a port to a server and lets you read and write to it from the terminal. How it works: First, exec sets up a redirect for /dev/tcp/$server/$port to file descriptor 5. Then, as per some excellent feedback from @flatcap, we launch a redirect from file descriptor 5 to STDOUT and send that to the background (which is what causes the PID to be printed when the commands are run), and then redirect STDIN to file descriptor 5 with the second cat. Finally, when the second cat dies (the connection is closed), we clean up the file descriptor with 'exec 5>&-'. It can be used to test FTP, HTTP, NTP, or can connect to netcat listening on a port (makes for a simple chat client!) Replace /tcp/ with /udp/ to use UDP instead.

get all pdf and zips from a website using wget
If the site uses https, use: $ wget --reject html,htm --accept pdf,zip -rl1 --no-check-certificate https-url

follow the content of all files in a directory
The `-q' arg forces tail to not output the name of the current file

Execute a command without saving it in the history
Yes, by correctly setting the HIST* variables you can make certain commands not saved in history. But that's complicated and easy to make a mistake. If you set HISTFILE= to blank, nothing in your current shell session will be saved in history. Although this is not a precise answer to the subject, but it's very simple.

send a circular

function to compute what percentage of X is Y? Where percent/100 = X/Y => percent=100*X/Y
This function make it easy to compute X/Y as a percentage. The name "wpoxiy" is an acronym of "what percentage of X is Y"

Extracting frames from a video as jpeg files
This command extracts 10 seconds worth of frames, starting from 00:15:45 position, from filename.avi and stores them into out_frames folder as jpeg files. Subtitles are turned off with -sid 999 option.

Mirror every lvol in vg00 in hp-ux 11.31

Backup a file with a date-time stamp
1. you don't need to prepend the year with 20 - just use Y instead of y 2. you may want to make your function a bit more secure: buf () { cp ${1?filename not specified}{,$(date +%Y%m%d_%H%M%S)}; }


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