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nmap get all active online ips from specific network
scan whole specific network for active online ips

ANSI 256 Color Test
Terminal Color tester using python, works with py2 and 3

mean color of an image
You can get the mean value for the colours in an image. Then you can determine, in general, how dark or bright is the image and run some other actions based on that. I'll recommend to readjust the brightness of the images using +sigmoidal-contrast option of imagemagick convert command.

peak amount of memory occupied by any process with "FOO" in its name
Show the maximum amount of memory that was needed by a process at any time. My use case: Having a long-running computation job on $BIG_COMPUTER and judging whether it will also run on $SMALL_COMPUTER.   http://man7.org/linux/man-pages/man5/proc.5.html VmHWM: Peak resident set size ("high water mark")

Extract multiple tar files at once in zsh
tar doesn't support wildcard for unpacking (so you can't use tar -xf *.tar) and it's shorter and simpler than for i in *.tar;do tar -xf $i;done (or even 'for i in *.tar;tar -xf $i' in case of zsh) -i says tar not to stop after first file (EOF)

Get duration of an audio file in seconds.
This is an alternative to #9131. ffmpeg didn't work on my .au files, though it did on the .wav ones. Also useful if you don't have ffmpeg but do have sox. Handily, sox already reports in seconds (decimal).

Get info about a GitHub user
In this example 'git' is the user name and the output format is YAML but you can change this to XML or JSON, eg: curl http://github.com/api/v1/json/usernamehere

list block devices
Shows all block devices in a tree with descruptions of what they are.

cleanup /tmp directory
Cleans all files in /tmp that have been accessed at least 2 days ago.

convert from decimal to hexadecimal


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