nerdnotes.org

Goal: generate a white noise .wav fille of 1.5 hours
In matlab:


% create a matrix with random values:
>> noise = 2 * rand(90 * 60 * 44100, 2, 'double') - 1;

% write the wav file with a sample frequency o 44.1kHz
>> wavwrite(noise, 44100, 16, 'noise.wav');

This process takes a while and it consumes quite some of your system RAM.

More efficient, in bash:

$ dd if=/dev/urandom count=5400 bs=176400 | sox -s -c 2 -r 44100 -t raw -w - noise.wav

This took only 2 minutes!

I’ve been searching for some ‘getopt’ examples on the internet. Many tutorials show the same basic tricks. I completely looked over the local documentation, which in fact has very nice examles for bash and tcsh:

#!/bin/bash

# A small example program for using the new getopt(1) program.
# This program will only work with bash(1)
# An similar program using the tcsh(1) script language can be found
# as parse.tcsh

# Example input and output (from the bash prompt):
# ./parse.bash -a par1 'another arg' --c-long 'wow!*\?' -cmore -b " very long "
# Option a
# Option c, no argument
# Option c, argument `more'
# Option b, argument ` very long '
# Remaining arguments:
# --> `par1'
# --> `another arg'
# --> `wow!*\?'

# Note that we use `"$@"' to let each command-line parameter expand to a
# separate word. The quotes around `$@' are essential!
# We need TEMP as the `eval set --' would nuke the return value of getopt.
TEMP=`getopt -o ab:c:: --long a-long,b-long:,c-long:: \
     -n 'example.bash' -- "$@"`

if [ $? != 0 ] ; then echo "Terminating..." >&2 ; exit 1 ; fi

# Note the quotes around `$TEMP': they are essential!
eval set -- "$TEMP"

while true ; do
        case "$1" in
                -a|--a-long) echo "Option a" ; shift ;;
                -b|--b-long) echo "Option b, argument \`$2'" ; shift 2 ;;
                -c|--c-long)
                        # c has an optional argument. As we are in quoted mode,
                        # an empty parameter will be generated if its optional
                        # argument is not found.
                        case "$2" in
                                "") echo "Option c, no argument"; shift 2 ;;
                                *)  echo "Option c, argument \`$2'" ; shift 2 ;;
                        esac ;;
                --) shift ; break ;;
                *) echo "Internal error!" ; exit 1 ;;
        esac
done
echo "Remaining arguments:"
for arg do echo '--> '"\`$arg'" ; done

De-installation is sometimes not so easy with APT. For example when you screwed up your mysql installation or lost mysql passwords you may want to reinstall mysql and start from scratch again. You probably installed mysql server using:

$ sudo apt-get install mysql-server

Then you might think that you need this command for removal:

$ sudo apt-get remove mysql-server

However, this is not the case. The mysql-server package is a sort of meta-package that makes sure that the latest (and greatest) available mysql server version will be installed. Currently, this means that you actually installed mysql-server version 5.0. Above command will only remove the meta-package, while mysql server 5 happily continues running on your system. To de-install the mysql-server, remove the package, the meta package pulled in:

$ sudo apt-get remove mysql-server-5.0

To also remove the configuration and the binary data, use instead:

$ sudo apt-get remove --purge mysql-server-5.0
# and for ubuntu Gutsy:
$ sudo apt-get purge mysql-server-5.0

Now that mysql server is ‘really’ gone, you can start over and install the mysql-server package:

$ sudo apt-get install mysql-server

This is a script that extracts the layers of a XCF file to individual PNG files. It uses xcftools (debian/ubuntu package):

#!/bin/bash

xcffile=$1

layers=`xcfinfo $xcffile  | awk '{ print $NF }'`

destdir=`dirname $xcffile`/layers
mkdir $destdir

for layer in $layers
do
        echo saving $layer to $destdir/$layer.png
        xcf2png -o $destdir/$layer.png $xcffile $layer
done

exit 0