Useful for quick calculations at the command line. $math_expr is any arithmetic expression (see sample output):

4.5*16+3^2

s(3.1415926/2)

More options in the bc man page.

Allows for quick mass renaming, assuming the user has some familiarity with regular expressions. Basically, it replaces the original_file_name in the output of ls with

"mv -v original_file_name new_file_name"

and passes the output to sh.

parses the output of ifconfig to show only the configured ip address (in this case from interface eth0).

the regexp is quick'n'dirty im sure it can be done in a better way.

--> this alias does not show your "internet ip" when you're in a nat-environment

cdrecord must be installed.

usefull alias:

now iso burning is like.

release upgrades are major upgrades as from 8.04 to 8.10 or from 8.10 to 9.04

update-manager-core must be installed:

in some cases you must edit '/etc/update-manager/release-upgrades' and set 'Prompt=normal'

It's sometimes useful to strip the embedded fonts from a pdf, for importing into something like Inkscape. Be warned, this will increase the size of a pdf substantially.

I tried this with only gs writing with -sDEVICE=pdfwrite but it doesn't seem to work, so I just pipe postscript output to ps2pdf for the same effect.

When you run a memory intensive application (VirtualBox, large java application, etc) swap area is used as soon as memory becomes insufficient. After you close the program, the data in swap is not put back on memory and that decreases the responsiveness. Swapoff disables the swap area and forces system to put swap data be placed in memory. Since running without a swap area might be detrimental, swapon should be used to activate swap again.

Both swapoff and swapon require root privileges.

helps you keep watch on the load of a system, without having to stare constantly at the terminal. The -d argument to watch highlights the difference from the last run, making it easier to note how the load is fluctuating. The sed command just strips off the information about how long the box has been up, and how many users are logged in.

Mount an smb share with this command. other options -ousername=$USERr,gid=$groupname,scope=rw

The arguments of "seq" indicate the starting value, step size, and the end value of the x-range. "awk" outputs (x, f(x)) pairs and pipes them to "graph", which is part of the "plotutils" package.

Displays six rows and five columns of random numbers between 0 and 1. If you need only one column, you can dispense with the "for" loop.

This example calculates the averages of column one and column two of "file.dat". It can be easily modified if other columns are to be averaged.

I use this to convert mp3 files to m4a files that can be used as ringtones on the iPhone. I've documented the process here: http://www.control-d.com/?p=60

Takes filenames and directory names and replace space to '_'.

The queryformat option can be used in a number of ways to find things like duplicate packages, wrong arch, or the exact package to pass to rpm -e, yum remove, etc.

Another combination of seq and awk. Not very efficient, but sufficiently quick.

"seq 100" outputs 1,2,..,100, separated by newlines. awk adds them up and displays the sum.

"seq 1 2 11" outputs 1,3,..,11.

Variations:

1+3+...+(2n-1) = n^2

1/2 + 1/4 + ... = 1