This uses mpg123 to convert the files to wav before burning, but you can use mplayer or mencoder or ffmpeg or lame with the --decode option, or whatever you like.

remove files with access time older than a given date.

If you want to remove files with a given modification time replace %A@ with %T@. Use %C@ for the modification time.

The time is expressed in epoc but is easy to use any other ordered format.

This command creates and burns a gapless audio CD with 99 tracks. Each track is a 30 second sine wave, the first is 1 Hz, the second 2 Hz, and so on, up to 99 Hz. This is useful for testing audio systems (how low can your bass go?) and for creating the constant vibrations needed to make non-Newtonian fluids (like cornstarch and water) crawl around.

Note, this temporarily creates 500MB of .cdda files in the current directory. If you don't use the "rm" at the end of the command, you can burn more disks using

Prerequisites: a blank CD-R in /dev/cdrw, sox (http://sox.sourceforge.net/), and cdrdao (http://cdrdao.sourceforge.net/). I'm also assuming a recent version of bash for the brace expansion (which just looks nicer than using seq(1), but isn't necessary).

Note the space before the command; that prevents your history eliminating command from being recorded. ' history -c && rm -f ~/.bash_history' Both steps are needed. 'history -c' clears what you see in the history command. 'rm -f ~/.bash_history' deletes the history file in your home directory.

For all of the jpgs in a directory, determine their size and if below a threshold remove them forcefully.

plays with bash arrays. instead of storing the list of files in a temp file, this stores the list in ram, retrieves the last element in the array (the last html file), then removes it.

Converts a .vdi file to a .vmdk file for use in a vmware virtual machine. The benefit: using this method actually works. There are others out there that claim to give you a working .vmdk by simply using the qemu-img command alone. Doing that only results in pain for you because the .vmdk file will be created with no errors, but it won't boot either.

Be advised that these conversions are very disk-intensive by nature; you are probably dealing with disk images several gigabytes in size.

Once finished, the process of using the new .vmdk file is left as an exercise to the reader.

Some malicious program appends a iframe or script tag to you web pages on some server, use this command to clean them in batch.

Check out the usage of 'trap', you may not have seen this one much. This command provides a way to schedule commands at certain times by running them after sleep finishes sleeping. In the example 'sleep 2h' sleeps for 2 hours. What is cool about this command is that it uses the 'trap' builtin bash command to remove the SIGHUP trap that normally exits all processes started by the shell upon logout. The 'trap 1' command then restores the normal SIGHUP behaviour.

It also uses the 'nice -n 19' command which causes the sleep process to be run with minimal CPU.

Further, it runs all the commands within the 2nd parentheses in the background. This is sweet cuz you can fire off as many of these as you want. Very helpful for shell scripts.

Remove your BASH history and then link it to /dev/null

Best way I know to get rid of .bash_history and don't allow bash to save the current one on exit

Edit: added ~/ before .bash_history, just in case... ;)

this string of commands will release your dhcp address, change your mac address, generate a new random hostname and then get a new dhcp lease.

USAGE: gate listening_port host port

Creates listening socket and connects to remote device at host:port. It uses pipes for connection between two sockets. Traffic which goes through pipes is wrote to stdout. I use it for debug network scripts.

Remove everything in current directory except files starting with "ca".

This helped me find a botnet that had made into my system. Of course, this is not a foolproof or guarantied way to find all of them or even most of them. But it helped me find it.

This command uses the recursive glob and glob qualifiers from zsh. This will remove all the empty directories from the current directory down.

The **/* recurses down through all the files and directories

The glob qualifiers are added into the parenthesis. The / means only directories. The F means 'full' directories, and the ^ reverses that to mean non-full directories. For more info on these qualifiers see the zsh docs: http://zsh.dotsrc.org/Doc/Release/Expansion.html#SEC87

A common mistake in Bash is to write command-line where there's command a reading a file and whose result is redirected to that file.

It can be easily avoided because of :

1) warnings "-bash: file.txt: cannot overwrite existing file"

2) options (often "-i") that let the command directly modify the file

but I like to have that small function that does the trick by waiting for the first command to end before trying to write into the file.

Lots of things could probably done in a better way, if you know one...