In this example I’m going to assume we are connecting to a remote database. Most protocols require three pieces of data to pull this off: a server, a username and a password. We are going to store these three pieces of data in a file called config.plain, encrypt this file (making config.aes), extract its variables and finally connect to our remote database.

I’m going to use the following example config.plain file:

SERVER=FooBar
USER=JOE
PASS=RANDOM

So we need to encrypt our config.plain file and turn it into config.aes (AES being the encryption standard we are using). The following example is cheerfully swiped from the example given over at Tombuntu.

>openssl aes-256-cbc -a -salt -in config.plain -out config.aes

So if we wanted to reverse this and decrypt the config.aes file on the command line we could run:

>openssl aes-256-cbc -d -a -salt -in config.aes

NOTE: For some reason the OpenSSL CLI doesn’t obey the Unix standard of specifying ‘-’ as a file name to output to the console. Omitting the ‘-out’ argument will instead output to STDOUT.

Putting it all together

The config.plain example file:

SERVER=FooBar
USER=JOE
PASS=RANDOM

The config.aes file (same as above but after encryption using the password ‘password’):

U2FsdGVkX19aTdTnSuV1p5R6DCQxp21yrlCc+9j9dap/ziojbiDP1SbSM+6HXF0T
PabsGQgSdV8Ir4rmMjgyFA==

The actual script file which does the decryption and performs the final actions on the data.
We are going to accept the master password from the command line (so we would run the below as ‘script password’ – assuming our script was called ‘script’ and the password was ‘password’). This is not the most secure method available since you can see the launch method of all applications running on the system using ‘ps’. If you want more security I would instead store your password in a system variable and use that instead of reading from the command line. If you wish to do this you can simply strip out all the lines that do error checking and use ‘KEY’ as a system variable to store the master password.

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#!/bin/bash
# USAGE: script <password>
# Do something with the associated config.aes script in a reasonably secure way
#
# Example config.plain content:
# SERVER=FooBar
# USER=JOE
# PASS=RANDOM
#
# Command to encrypt config.plain -> config.aes
# openssl aes-256-cbc -a -salt -in config.plain -out config.aes
 
# Do some housekeeping to check we launched with the requisite number of arguments
if [ "$#" -ne 1 ]; then
	echo "USAGE: $0 <password>"
	exit 1
fi
KEY="$1"
 
# Import the variables from our decrypted stream
STREAM=`openssl aes-256-cbc -d -pass "pass:$KEY" -a -salt -in config.aes`
if [ "$?" -ne 0 ]; then
	echo "Invalid password specified to decrypt configuration file. Aborting."
	exit 1
fi
source <(echo "$STREAM")
 
# REPLACE THE STUFF BELOW THIS LINE WITH WHAT YOU WANT TO DO WITH YOUR SECURE VARIABLES
echo "Server: $SERVER"
echo "Username: $USER"
echo "Password: $PASS"

So onto the diff-merging candidates:

VimDiff (part of Vim)

Doesn’t work too well with Unison. I can’t get gnome-terminal (my terminal of choice) to execute synchronously so I was forced to fall back on XTerm instead.

After using XTerm I immediately hit upon a problem: there is no sensible way of outputting the results of a merge in VimDiff. Which is a pity because I do prefer VIM as an editor but this lack of functionality is annoying (yes I could have used a wrapper script but I’m trying to keep this simple).

Meld

Very pretty but lacks features such as ‘Use Left-hand-side-file for all changes’ and some of the other filtering options provided by KDiff3.

Also, like, VimDiff, does not provide any sensible output mechanism of the eventually merged file.

KDiff3

Not as good looking as Meld but provides pretty much everything I want in a merge program including the all important merged file output that Unison requires.

Can get a little annoying though with its insentient pop-up boxes. I wish there were a ‘Dont show this option again’ option to each. KDE is usually quite good with this so I’m not sure why KDiff3 managed to escape this unspoken standard.

Conclusion

So how to use KDiff3 with Unison? First install kdiff3:

apt-get install kidff3

Then open your Unison profiles .prf file and insert the following:

merge = Name * -> kdiff3 CURRENT1 CURRENT2 -L1 'Local File' -L2 'Remote File' -o NEW -m
confirmmerge = true

If you are comfortable with KDiff3 you could remove the ‘confirmmerge’ line which forces Unison to double check you actually want to accept the changes.

The downside to the above interactive merging process is there is no sensible way to preview the merge in Unison (the ‘View Merge’ button in the confirmation dialogue). For now though its preferable to not having this functionality at all.

Since most Linux shells have a major problem with doing this in a sensible way, the following (on my box called simply ’0′) takes any input (either from files or via a pipe) and converts the characters.

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#!/usr/bin/perl
# From: http://hash-bang.net/2009/04/converting-nullconverting-null/
# Author: Matt Carter <m@ttcarter.com>
while (<>) {
	s/\n/\x00/g;
	print;
}

So now commands like:

find -type f | 0 | xargs -0 | mplayer

work perfectly (in the above case to play all files in directories recursively.

You may well ask why I don’t use the simple ‘-print0′ argument for the find program – because it doesn’t work when using later pipes.

For example if i wanted to sort the above, ‘sort’ would see the null symbol as a regular character.

So ’0′ works nicely in this case:

find -type f | 0 | sort | xargs -0 | mplayer

Or even:

find -type f | 0 | shuffle | xargs -0 | mplayer

To play all files recursively, in random order. See the article on shuffle for the source code of that filter.

The below operates like a simple Unix filter taking an array of data (separated by newlines) and returning a quickly sorted output.

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#!/usr/bin/perl
# Usage: cat file | shuffle
# From: http://hash-bang.net/2009/04/shuffling-shell-inputshuffling-shell-input/
# Return a shuffled version of the input stream
# Author: Matt Carter <m@ttcarter.com>
 
sub fisher_yates_shuffle {
	my $array = shift;
	my $i;
	for ($i = @$array; --$i; ) {
		my $j = int rand ($i+1);
		next if $i == $j;
		@$array[$i,$j] = @$array[$j,$i];
	}
}
 
while(<>) {
	chomp;
	push @input, $_;
}
 
&fisher_yates_shuffle(\@input);
print join("\n",@input);

For example:

ls | shuffle

Returns a randomized list of files in the current directory.

The downside to having a box for development though is the constant config of apache to host these sites, most of which require absolute links (e.g. ‘/css/style.css’) to function.

The Apache snippet below sets up dynamic sub-domains which can be changed without reloading Apache every time you add, remove or update anything something. Simply drop your sites inside /var/www whenever you want a new subdomain. Alternatively you can symlink if they are hosted elsewhere on the box.

Its pretty easy to install, simply paste the below in your /etc/apache2/apache.conf file…

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# Easy virtual host config
# See http://hash-bang.net/2009/03/easy-apache-virtualhosteasy-apache-virtualhost/
<VirtualHost *>
DocumentRoot /var/www/
ServerAdmin admin@localhost
Options +FollowSymLinks -Indexes
LogLevel debug
ServerAlias localhost
ServerName localhost
RewriteEngine  on
RewriteLogLevel 3
RewriteCond    %{HTTP_HOST}  ^localhost
RewriteRule    ^(.*)$        /www/$1 [L]
RewriteCond    %{HTTP_HOST}  ^www.*
RewriteRule    ^(.*)$        /www/$1 [L]
RewriteCond    %{HTTP_HOST}  ^(.*)\.localhost
RewriteRule    ^(.*)$        /%1/$1 [L]
</VirtualHost>

Now add your servers to the /etc/hosts file:

127.0.0.1      server.localhost

Now any directory you place in the /var/www directory automatically becomes a subdomain. You can now visit http:///server.localhost as a fully fledged webhost.

If you want to use another name than the rather boring ‘localhost’ simply replace the text in both text pastes above.

If only there were a way of removing that /etc/hosts hack it would mean zero config from then on. If anyone has any ideas do let me know. The addition to the hosts file seems to need applying if you are working from the same box the Apache server resides on. If you arn’t and the box is a local dedicated server its not needed at all and domains can be added and removed as necessary.

Who amongst us has not at some point done something like:

> rm * .tmp

or

> rm *>tmp

The former makes the mistake of a space between the dot and the ‘tmp’ part and the latter the accidental holding down of the shift key while pressing the intended full stop.

While searching for an alternative for the I-have-done-this-too-many-times-and-now-its-embarrassing approach of nuking everything with the ‘rm’ command its time i did something about it.

Inserting the following in your ~/.bashrc file will remap the ‘rm’ command to a slightly safer move-to-trash like behavior. Its not comprehensive but it has saved my life on more than one occasion.

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# Trash support by Matt Carter <m@ttcarter.com
# Source and information: http://hash-bang.net/2009/03/trash-with-bash
function trash() {
	if [ -d "$HOME/.trashcan/$1" ]; then
		# Already exists in bin - remove
		rm -r "$HOME/.trashcan/$1"
	fi
	mv --target-directory=$HOME/.trashcan/ -- "$@"
}
alias "rm=trash"
alias "emptytrash=/bin/rm -rf $HOME/.trashcan/* $HOME/.trashcan/.??*"
alias 'rm!=/bin/rm -r'
mkdir ~/.trashcan 2>/dev/null

Now the command ‘rm’ moves files into ~/.trashcan. You can also use the command ‘rm!’ when you really mean delete immediately and the utility command ‘emptytrash’ to clean everything out.

This command is designed as a drop-in replacement for the slightly cryptic pgrep and pkill commands.

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zap() {
	# Usage: zap [SIGNAL|-NUMERIC|shoot] <fgrep>
	SIGNAL=''
	case "$1" in
		shoot|-0) SIGNAL='SHOOT';;
		term|-15) SIGNAL='TERM';;
		kill|-9) SIGNAL='KILL';;
		hup|-1) SIGNAL='HUP';;
	esac
	if [ "$SIGNAL" != '' ]; then
		shift
	else
		SIGNAL='SHOOT'
	fi
	PROCS=`ps ax -eo pid,comm | fgrep "$1"`
	MODE=0
	for DATA in $PROCS; do
		if [ "$MODE" -eq 0 ]; then
			PID="$DATA"
			MODE=1
		else
			CMD="$DATA"
			MODE=0
			if [ "$SIGNAL" == 'SHOOT' ]; then
				echo -n "Shooting #$PID - $CMD..."
				kill $PID
				sleep 1
				kill -9 $PID
				echo "Shot"
			else
				echo -n "Killing #$PID - $CMD..."
				kill $SIGNAL $PID
				echo "Killed"
			fi
		fi
	done
}

To install it simply dump the above text inside your existing ~/.bashrc file.

Usage is quite simple:

To politely kill all processes (then force-killing if it still does not die) containing the string ‘gnome’:

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zap gnome

To just kill-forcefully:

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zap -9 gnome

Admin level access is obviously required in order to install software without relentless ‘Program X requires administrative access’ UAC prompts.

Like most things in Vista the solution is exceptionally stupid and requires significant trips with Google to rather obscure second-hand Microsoft knowledge base articles.

The overview is something like this:

First create the autorun.inf file:

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[autorun] 
open=invoke.bat 
icon=autorun.ico,0
label=Setup computer from USB disk

So this file simply sets up the autorun.inf file which contains exactly what to list in the Vista ‘Autoplay’ dialog when the USB disk is inserted. You will probaly want to rename the ‘Label’ line and perhaps put a pretty icon on your disk called ‘autorun.ico’.

Now create your actual batch file that you wish to run as admin and call it ‘setup.bat’.

As a small note of caution. For some reason Vista does not change to this files active working directory when executing. I can really think of no reason this behavior exists so you might want to add the following rather cryptic command as the first in the batch file. This changes the active directory into the current batch file (in this case ‘setup.bat’) directory.

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@ECHO OFF
cd /d %~dp0

There obvious when you think about it isn’t it. Shame on you for not knowing about the handy and invisible shell variable “~dp0″. I am sure there is a long and interesting story about why this variable is so called and why it doesnt show up with the rest of things when you type ‘set’. This is why I switched to Linux some time ago.

Anyway, now we’ve done that create a shortcut to the ‘Setup.bat’ file and rename it to ‘setup.lnk’ (remember that the ‘.lnk’ bit will always be invisible to you anyway so when you rename in explorer all you will see is the ‘setup’ bit sans extension).

Open the shortcuts properties and hit the ‘Advanced’ button. Tick the ‘Run as Administrator’ box.

Finally, lets join it all together by creating the ‘Invoke.bat’ file which runs the shortcut (which will in turn run the ‘setup.bat’ program after asking via UAC for administrative permission).

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@ECHO OFF
"Setup.lnk"

Now save everything and remove you disk (safely) and re-insert. You will now be able to run the ‘setup.bat’ file which should contain all your auto-install scripts after a UAC admin prompt. Yey.

For reasons passing understanding though the programmers of this excellent system have desided not to provide pretty URL’s out of the box. Getting infomation on this is a little tricky so here is my take on the situation.

Simply dump the following into a file called ‘.htaccess’ (Note the starting Dot) in the root path (thats the one at the very start of your path tree that should contain the ‘system’ folder).

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RewriteEngine on
RewriteCond %{REQUEST_FILENAME} -f
RewriteRule ^(.*)$		- [L]
 
RewriteCond $1 !^(index\.php|images|robots\.txt)
RewriteRule ^(.*)$ /index.php/$1 [L]

As with most mod_rewrite hacks you will need that enabled on an apache server. Its very rare to find a hosting company that doesn’t use this setup so you should be fine.

You will also need to change the following variable to a blank value in the system/application/config/config.php file:

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$config['index_page'] = '';

And you’re done. From now on your Urls are addressed in the form: http://SITE/CONTROLLER/METHOD/VALUE1/VALUE2 (e.g. http://mysite.com/users/edit/123123)

The PHP manual suggests that two pages be created: header and footer, and that these are included at the beginning and end of each document.

Thus for a ‘contact us’ page the contact.php file would look something like:

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<? include("header.php") ?>
... The contact pages HTML ...
<? include("footer.php") ?>

While this does work, there are easier ways to accomplish the same thing and still maintain compatibility with editors such as Dreamweaver which seems to choke on even a small amount of PHP.

The under-documented auto_prepend_value and auto_append_values get a brief mention in the ini directives documentation but I thought it would be nice to show an example of how these can be used in the wild,

Adding the following to either an existing ‘.htaccess’ (note the starting dot) or downloading the below file will do pretty much the same as the above contact.php file example did only without needing to specify the files in the beginning and ends of each separate file.

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php_value auto_prepend_file "header.php"
php_value auto_append_file "footer.php"

And as with all .htaccess directives you can override these on a directory basis. So if you need a different header and footer when inside the ‘invoices’ directory dump another copy of the above into that directory changing it as needed.

And yes this method can be merged with the previous post to work with the URL prettifier.

http://somewhere.com/contact.php

Is soooo 1990′s.

URL prettification has always been seen to be the exclusive domain of larger frameworks but with Apache it really isn’t that hard.

Simply paste the following into a file named ‘.htaccess’ (note the starting ‘dot’) and dump it in your website to allow the extension of your script to be ‘guessed’ by Apache should it not be provided.

This hack obviously requires mod_rewrite but since every hosting provider and their dog provides this these days i would say not having it enabled would be the exception rather than the rule

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RewriteEngine On
RewriteBase /
 
RewriteCond %{REQUEST_FILENAME}.php -f
RewriteRule ^(.*)$		$1.php [L]

ASP, Python and Perl people either add your .asp, .py or .pl sections under or above the .php bits or simply replace them.

There, now we can use:

http://somewhere.com/contact

But the old way (with .php extension) is still valid too.

Finally we put an end to this silly file extension nastiness.
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