HACKTUX notes from the trenches

Stickers Related to Free Software Projects (Mirror)

This book includes a set of stickers related to free software projects. Now, you may remove Microsoft sticker from your computer (computers are only not designed for the Microsoft Windows) and choose some sticker of this book to replace it. If you want to participate in Sticker Book Project, you can send your sticker/s to stickers@pikao.org.

Original Sites

• Mirror for: http://pikao.org/stickers/
• Subversion: http://stickersbook.googlecode.com/svn/trunk/

Mirrored Files

• sticker_book.pdf
• sources.tar.gz
• book_source.odg

Bash supports various string operations. Here are some examples to get you started quickly. For detailed information, see the official Bash documentation.

String Assignment

Below are a few ways to assign a string variable.

bash$ OS=Linux

Use quotes to encapsulate strings with spaces:

bash$ OS='CentOS 4.6'

Or, use double quotes to allow for variable expansion:

bash$ DISTRO="Fedora"
bash$ OS="$DISTRO Linux"
bash$ echo $OS
Fedora Linux

String Length

Determining the length of your string is easy:

bash$ PROG="Bash"
bash$ echo ${#PROG}
4

You can also use expr:

bash$ expr length $PROG
4

Substring Extraction

Below are some examples of substring expansion in the form of ${string:position} and ${string:position:length}. String indexing starts at zero!

bash$ PROG="Bash"
bash$ echo ${PROG:0}
Bash
bash$ echo ${PROG:1}
ash
bash$ echo ${PROG:1:2}
as

Testing Strings

Test if a string is of length 0

[ -z $STRING ]

Test if length of string is not zero:

[ ! -z $STRING ]
[ -n $STRING ]

Test if strings are equal.

[ $STRING1 == $STRING2 ]

Remember to use quotes if the string has spaces or escape characters (newlines).

[ "$STRING1" == "$STRING2" ]

The 'not equal; operator is !=

[ $STRING1 != $STRING2 ]

If you are running Fedora and need Apache's HTTP web server, you have a couple of options. One, you can install Fedora's pre-built RPMs. Two, you can compile Apache to meet your specific needs.

Compiling Apache can improve performance and security. But, if you are starting out or need to get up and running quickly, use Fedora's RPMs.

Quick Install

To quickly install Fedora's Apache packages, install the 'Web Server' Yum group. This will install HTTPD with support for PHP, mod_perl, mod_ssl, and mod_python. The Web Server group also contains squid and weblizer.

yum groupinstall "Web Server"

If you want more control over the packages you need, install them one at a time. First, install HTTPD and then add on the modules you need.

yum install httpd
yum install mod_ssl mod_python

Apache Configuration

If you are feeling lazy and want to use a GUI, Fedora provides a graphical interface for configuring Apache. Install system-config-httpd:

yum install system-config-httpd

Then, run the tool as root:

/usr/bin/system-config-httpd

You can also configure the httpd.conf file manually. See the Apache documentation for details on how to configure your web server.

vim /etc/httpd/conf/httpd.conf
vim /etc/httpd/conf.d/README

Start Apache

You can set Apache to start at boot using chkconfig:

chkconfig httpd on

Finally, start Apache with the service command:

service httpd start

For more information, see Fedora's official documentation or the Fedora Documentation Project's Wiki.

Arrays in Bash are quite simple. Here are some examples to get you going. The official Bash documentation has more details and examples.

Initialize an entire array:

bash$ DAYS=(mon tue wed thu fri sat sun)

There are two ways to reference an entire array:

bash$ echo ${DAYS[@]}
mon tue wed thu fri sat sun
bash$ echo ${DAYS[*]}
mon tue wed thu fri sat sun

Initialize array element

bash$ ARRAY[0]="Fedora"
bash$ ARRAY[1]="RedHat"
bash$ ARRAY[2]="CentOS"

Display an element

bash$ echo ${ARRAY[0]}
Fedora

Get the length of an array:

bash$ echo ${#ARRAY[@]}
3

Get the length of an array value based on index:

bash$ echo ${ARRAY[0]}
Fedora
bash$ echo ${#ARRAY[0]}
6

Get the subset of an array through trailing substring extraction:

bash$ echo ${ARRAY[@]:0}
Fedora RedHat CentOS
bash$ echo ${ARRAY[@]:1}
RedHat CentOS
bash$ echo ${ARRAY[@]:2}
CentOS

Below are examples of the Bash for loop in action. If you need more help, see the official Bash documentation for an introduction to Bash programming.

Examples

Echo all jpg files in the current folder:

for JPG in *.jpg; do
  echo $JPG
done

Count a list of numbers:

for NUM in $(seq 1 10); do
  echo $NUM
done

One liners work as well:

for n in $(seq 3); do echo $n; done

Iterate through the process ID's for httpd and kill them:

for PID in $(ps -C httpd | awk '/httpd/ { print $1 }'); do
  kill -TERM $PID
done

List arguments to a function named showarg:

showarg() {
  for ARG in $@; do
    echo $ARG
  done
}

Loop through folders and back them up using tar:


DATE=$(date +'%Y-%m-%d')
for DIR in /etc /var /root; do
  tar -czvf /backups/$DIR_$DATE.tgz $DIR
done

As of version 5.10.0-RC2, Perlcc is no longer distributed with Perl. This means that Fedora 9 does not include perlcc. Here is the official statement regarding perlcc from CPAN.org:

Removal of the bytecode compiler and of perlcc

perlcc, the byteloader and the supporting modules (B::C, B::CC, B::Bytecode, etc.) are no longer distributed with the perl sources. Those experimental tools have never worked reliably, and, due to the lack of volunteers to keep them in line with the perl interpreter developments, it was decided to remove them instead of shipping a broken version of those. The last version of those modules can be found with perl 5.9.4.

However the B compiler framework stays supported in the perl core, as with the more useful modules it has permitted (among others, B::Deparse and B::Concise).

Sources
CPAN.org: perldelta - what is new for perl 5.10.0

Fedora 9 provides OpenJDK!
See the Fedora Java FAQ for details: http://fedoraproject.org/wiki/JavaFAQ

Place these settings in ~/.vimrc to enable and configure spell checking in Vim. Comments start with double quotes. For more, open vim and type :help spell

Enable Spelling

set spell

Enable Spellfile

set spell spelllang=en_us
" zg to add word to word list
" zw to reverse
" zug to remove word from word list
" z= to get list of possibilities
set spellfile=~/.vim/spellfile.add

Set Colors

highlight clear SpellBad
highlight SpellBad term=standout ctermfg=1 term=underline cterm=underline
highlight clear SpellCap
highlight SpellCap term=underline cterm=underline
highlight clear SpellRare
highlight SpellRare term=underline cterm=underline
highlight clear SpellLocal
highlight SpellLocal term=underline cterm=underline

Fedora 9 comes with two drivers that can be used in /etc/X11/xorg.conf to support your Nvidia card.

1. NV: http://xorg.freedesktop.org/wiki/nv
2. Nouveau: http://nouveau.freedesktop.org/wiki/

Although these two drivers work, they have their limitations. It is best to install the Nvidia driver from Nvidia.com. You can either build the source from Nvidia's Driver Website, or use Livna.org to install a binary kernel module.

Livna's Binary Nvidia Driver

To use Livna.org's binary driver, install Livna's release package for Fedora 9. This will provide you with access to Livna.org's Fedora 9 YUM repository using /etc/yum.repos.d/livna.repo.

rpm -ivh http://rpm.livna.org/livna-release-9.rpm

Next, install the Nvidia kernel module and all of it's dependencies:

sudo yum install kmod-nvidia

Then, use the nvidia-xconfig script to configure /etc/X11/xorg.conf. This will configure /etc/X11/xorg.conf with the 'nvidia' driver and it's options.

sudo /usr/sbin/nvidia-xconfig

Finally, reboot your system. You should see the Nvidia driver loading during boot. If you have any X errors, check /var/log/Xorg.log. If you want to tweak your driver, OpenGL or display settings, use nvidia-settings.

sudo /usr/bin/nvidia-settings

I have posted instructions on how to install Flash on Fedora 9, but Laurent Armstrong wrote me to share his script for automating the Flash install process -- and more. Laurent's script is interesting, so you might want to check it out: http://vegasoft.ca/howto/Install_f9

Thanks for the email, Laurent!

Kuba wrote me from Poland, with some interesting ways to limit the scope of Bash's $RANDOM variable. I updated my instructions for generating random numbers in Bash to include Kuba's suggestions.

Thanks, Kuba!

Todd Zullinger, recently showed me how to change the Fedora 9 GDM background using a gconftool-2 one liner. So, I updated my Fedora 9 GDM instructions to include Todd's suggestion.

Thanks Todd!

Getting an "Argument list too long" error using Linux?

This is because you are passing too many arguments to an executable.
For example, using *.html below results in too many arguments to /bin/rm:

rm *.html
bash: /bin/rm: Argument list too long

One solution is to use Bash control loops to iterate through arguments.

for HTMLFILE in *.html
> do
> rm -f $HTMLFILE
> done

Alternatively, the find command can be used to manipulate large data sets.
The following find command is identical in result to the for loop shown above.

bash$ find ./ -maxdepth 1 -name '*.html' -exec rm -f {} \;