Perl : making all filenames lowercase

Renaming all files in a directory to lowercase names in a directory recursively.

find . -type f -exec perl -e 'rename($_, lc) || warn "$_: $!\n" for @ARGV' {} \;

MySQL : root password reset

Here's what you need to do in case you forget the root user password of mysql.

# stop mysql service
/etc/init.d/mysql stop

# Start to MySQL server w/o password
mysqld_safe --skip-grant-tables &

# Connect to mysql server using mysql client
mysql -u root

# Setup new MySQL root user password
mysql> use mysql;
mysql> update user set password=PASSWORD("NEW-ROOT-PASSWORD") where User='root';
mysql> flush privileges;
mysql> quit

# Stop MySQL Server
/etc/init.d/mysql stop

# Start MySQL server and test it
/etc/init.d/mysql start
mysql -u root -h localhost -p

Web Development : Saving sessions in database

Some advantages of saving sessions in database.

1. The session data is more secure as a potential hacker must be
able to log into the database before he can access anything.
2. The use of multiple servers would not create a problem as all
session data now resides in a single central place and is accessible
by all servers.
3. It is much easier to query the database should the site
administrator require information about current sessions or current
users.

--
Regards,
Ketan

Linux : setting up rdist

rdist command is very helpful in synchronizing filesystems on two
server. rdist stands for remote distribution. Many useful options are
available with the command.

See `man rdist` for more information about the command.

This is how I set up rdists :-)

My crontab entry
10 * * * * rdist -f $HOME/bin/rdist_file > /dev/null

###rdist_file contains

## these are comments
/path/of/source/file -> target_server1 install
-onochkowner,nochkgroup,nochkmode /path/to/the/target/file;

### file rdist ed to target_server2
/path/of/source/file -> target_server2 install
-onochkowner,nochkgroup,nochkmode /path/to/the/target/file;

Linux : splitting a log file

To split a file into small files of 5000 lines, use this,

% split -l 5000 file

This creates files like xaa, xab etc.

My website

I have launched my website.

http://www.carvingIT.com.

Your feedback is welcome !

Leaving my job

After working with ANSYS-Fluent Inc. for more than 7 years, I have
decided to start working as a Consultant in the field of Linux,
Apache, MySQL, Perl/PHP. After joining Fluent, I developed liking for
the Linux platform and the open source technologies.

During my tenure with Fluent, I wrote many complex perl scripts and
modules. Now, I think Open Source is the field where I can help the
community and grow individually as well.

html source and bandwidth usage

1 character equals 1 byte.  Extra newline in html source means one extra byte sent to client.
If a website gets some 400 pageviews per day, you send 400x30 (sligtly more than 1 Kb) extra bytes per month.
This means 1 character may mean 1 Kb of bandwidth usage per month for a website of low traffic. More the traffic more the size associated per character.

Therefore, to save the bandwidth and to improve loading speed of your pages, optimize your templates and html !

mod_perl : DBI.so/GD.so can't be loaded

mod_perl can not load modules like DBI.so or GD.so ? The reason this happens is that the perl version with which you compiled mod_perl may not be the same that you are using currently. Whenever you upgrade perl, you have to recompile mod-perl and may be re-install these modules. That may solve this problem.

If you are using Apache2, you are lucky in the sense that you won't have to compile apache with mod_perl. Just re-build perl and install it and then build mod_perl and install.

PHP : Handling multiple select menu

Thought of putting a code to illustrate handling multiple select menus with php.

Note the square brackets and the multiple="multiple" part in the form.

HTML form
---------

<form action="some_action_file.php" method="post">
<select name="select_name[]" multiple="multiple">
<option value="a">a</option>
<option value="b">b</option>
<option value="c">c</option>
<option value="d">d</option>
</select>
<input type="submit" value="Submit" />
</form>
PHP part
----------
<?php ## some_action_file.php foreach ($_POST['select_name'] as $select_name){ echo "$select_name<br />"; ## prints all the selected values; one per line } ?>

Perl : Removing last newline in while

Here's a way to check if we are at the last iteration and removing the newline if true, while iterating through lines.

while(<>){
chomp if eof; ### eof returns 1 if next read on filehandle returns end of file
print;
}

Perl : Locating a perl module file

How do you find out exactly where a perl module file is ? Following example searches Template.pm in the paths where perl modules are installed.

find `perl -e '$,="\n";print @INC'` -name Template.pm

Note

The perl command is in back-ticks. This is an example of command execution within a command.

Networking : Switches versus Hubs

A few days back, I replaced hub with a switch in my small LAN at home. Although it's just a plug and play sort of switch, I had to do some configuration changes so that computers could ping each other. I spent a lot of time solving connectivity problems :-) Learnt a lot about how switches work in the process.

I can think of following differences between a hub and a switch.

1. Hub requires no knowledge of how it works. It's easy to install. The same is not true with switches. Even if the manual s
ays "plug and play switch", it's better to know how switches work.

2. You may have to configure your NICs (network cards) so that the switch communicates. To configure network cards, you need
 to learn what to configure.

3. Switches offer you a learning opportunity :-). In the process of making your network work for you, you'll learn people me
an by words like duplex auto-negotiation and speed.

4. If you are required to troubleshoot, you learn still more. In that case, you'll learn commands like ethtool, ifconfig, tr
aceroute, ifup, ifdown etc.

5. Conlusion is, Switches are better than hubs not only because of the reasons you read on the net, but they also teach you
networking.

Linux : renaming files with rename in a loop

Following command (a small shell script) changes file extensions of all files from .TXT to .txt in the working directory.

for file in `find . -type f -name "*.TXT"`; do rename .TXT .txt $file; done

The above works in bash. For use in other shells, you'll have to change the looping sytax.

Perltidy

Perltidy is a great utility for formatting your perl codes. It splits long lines into short lines, does formatting with blocks thus increasing the readability of your codes. You can save your own settings related to formatting in a file called .perltidyrc. This file should saved in $HOME directory.

For more information and download of Perltidy, visit
http://perltidy.sourceforge.net/

Perltidy is coool !

Linux : Killing processes

Sometimes you have to kill several processes generated by a service/server (the main process) and killing one process is not enough. Recently, I had trouble with 'apachectl stop'. This would not stop all the processes of httpd for some strange reason. Killing all processes by entering the process id's would take quite some time. I figured a way out -

Here's the time-saver

ps -ef | grep httpd | awk '//{print $2}' | xargs kill

You can use the same logic for other processes. You need to replace httpd with ..... you know. As you can see, awk separates just the process ids and it becomes easier for us to kill the processes !

Perl : Is this module Installed ?

How do you check if a certain perl module is installed and is in @INC ?

On the command-line, issue this command

perl -e 'use X::Y'

X::Y is the module
With -e, you can executes the perl code in quotes on command line.

If the module is found, there won't be any errors (no output).

Perl : Generating password with a subroutine

A subroutine to generate a password :-) When you find it hard to create one.

sub generatePassword
{
    my $passwd_size = shift;
    my @alphanum = ('a'..'z', 'A'..'Z', 0..9,'!','#','$','%','&','*','@','`');
    my $password = join '', map $alphanum[rand @alphanum], 0..$passwd_size;

    return $password;
}

Usage

&generatePassword(10); ### returns password of 10 chars

Perl : Installing CPAN modules

This post if for those who find it hard or don't know how to install CPAN modules.

1 Become root

2. Run

perl -MCPAN -e shell

First time you run this command, you'll be asked some questions regarding where to download/extract files etc. Just select the defaults.

3. This opens the cpan prompt. Now, run

install Module::Name

That's all you have to do. Isn't this really simple ?

osix.net : A good website for programmers

I would like everybody to know I am a registered user of www.osix.net. There, I have cleared Geek Level 6 from the "Geek Challenge". These levels are programming puzzles on solving which you earn some reward points. You can exchange these reward points for hints from other geeks (experts), creating polls,  email address or pop access to email. There are some other redemption possibilities.

A great site for geeks !

My profile there
http://www.osix.net/modules/viewprofile/?name=ketan404