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Create a directory and go inside it
$_ expands to the last argument of the last command that was executed

Get a list of IP Addresses that have failed to login via SSH
This command shows a sorted list of the IP addresses from which there have been authentication errors via SSH (possible script kiddies trying to gain access to your server), it eliminates duplicates so it's easier to read, but you can remove the "uniq" command at the end, or even do a "uniq -c" to have a count of how many times each IP address shows in the log (the path to the log may vary from system to system)

Calculate N!
Same as the seq/bc solution but without bc.

Convert a videos audio track to ogg vorbis.
Assumes you have ffmpeg and oggenc. Similar to other scripts here, but this time outputting to Ogg Vorbis. I added the variable assignment for a nice output name. This is part of an interactive bash script I have with a few little multimedia tasks in it. http://www.dward.us/software/VSAK.sh

Limit memory usage per script/program
When I'm testing some scripts or programs, they end up using more memory than anticipated. In that case, computer nearly halts due to swap space usage, and sometimes I have to press Magic SysRq+REISUB to reboot. So, I was looking for a way to limit memory usage per script and found out that ulimit can limit memory. If you run it this way: $ $ ulimit -v 1000000 . $ $ scriptname Then the new memory limit will be valid for that shell. I think changing the limit within a subshell is much more flexible and it won't interfere with your current shell ulimit settings. note: -v 1000000 corresponds to approximately 1GB of RAM

List files above a given threshold
List files above a given size threshold.

Get your external IP address without curl
Curl is not installed by default on many common distros anymore. wget always is :) $ wget -qO- ifconfig.me/ip

Find the package that installed a command

Color STDERR in output
This command will take the output of a command and color any STDERR output as a different color (red outline in this case)

Filter IPs out of files


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