CodeWord: Apokalyptik

Bash Coding Convention ../

We use dirname() a lot in php to make relative paths work from multiple locations like so. The advantages are many:

require dirname( dirname( __FILE__ ) ) . '/required-file.php';
$data = file_get_contents( dirname(__FILE__).'/data/info.dat');

But in bash we often dont do the same thing, we settle for the old standby “../”. Which is a shame because unless your directory structure is set up exactly right, and you have proper permissions, and you run the command from the right spot, it doesnt work as planned. I think part of the reason is that its not obvious how to reliably get a full path to the script from inside itself. Another reason is that ../ is shorter to type and easier to remember. Finally there’s always one time scripts for which this methodology is overkill. But if you’re planning to write a script which other people will (or might) be using, I think it’s good practice to do it right. Googling for things you’d think to search for on this subject does not yeild very informative results, or incomplete (incorrect) methods… so… here’s how to do the above php in bash:

source $(dirname $(dirname $(readlink -f $0)))/required-file.sh
data=$(cat $(dirname $(readlink -f $0))/data/info.dat)

Hope this helps someone

As a side note, the OSX readlink binary functions differently. You’ll want to use a package manager to install gnu coreutils, and iether use greadlink, or link greadlink to a higher precedence location on your $PATH (I have /opt/local/bin:/opt/local/sbin: at the beginning of my $PATH)

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Simple TCP Daemon Example

Using some stuff I’ve covered in the past on my blog here’s a simple way to put up a daytime server (well to put any service onto a tcp port. I haven’t looked into its bi-directional capabilities yet, this was just sort of a proof-of-concept…

$ apt-get install ipsvd
$ wget http://blog.apokalyptik.com/files/daemonize/daemonize.c
$ cc daemonize.c -o daemonize
$ ./daemonize /var/run/daytime.pid /var/log/daytime.log 'tcpsvd 0 13 date'

start/stop and/or monit script are an extremely short jump from there… And kind of trivial/menial… so I leave that as an exercise to you… if you care

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This deserves some link love

Andy bogged a piece of advice that I have him which I got from Barry… and if you want to know how to get the true absolute path to the real location of the current script is from inside of it (like phps realpath and __FILE__) I suggest you check it out

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As Close to A Real Daemon As Bash Scripts Get

I’ve written a little something which is gaining some traction internally, and I always intended to share it with the world. So… Here. daemon-functions.sh

What it does is allow you to write a bash function called “payload” like so:

function payload() {
while [ true ]; do
checkforterm
date
sleep 1
done
}
source path/to/daemon-functions.sh

Once you’ve done that it all just happens.  daemon-functions gives you logging of stderr, stdout, a pid file, start, stop, pause, resume, and more functions.  when you start your daemon it detaches completely from your terminal and runs in the background.  Works very simply with monit straight out of the box.  you can have as many daemons as you wish in the same directory and they wont clobber each other (as the pid, control, and log files all are dynamically keyed off of the original script name.)  Furthermore inside your execution loop inside of the payload function place a checkforterm call at any place which it makes sense for your script to be paused, or stopped. it can detect stale pid files and run anyway if the process isnt really running.  As an added bonus you dont actually have to loop inside payload, you can put any thing in there, have a script thats not a daemon, but will take an hour, day, week, month to finish? stick it in, run it, and forget it.

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building sed for osx

I work in linux a lot… not bsd. So the OSX (bsd style) implementation of sed really throws me for a loop when I go text-file-spelunking, whats worse is that my scripts using sed aren’t portable between the two OSs.

A quick googling this morning landed me here: http://wiki.octave.org/wiki.pl?OctaveForMac which gives perfectly good instructions on installing sed. except it didnt work. I grabbed the latest version of sed (4.1.5) and got the error

sed: 1: "install_sh=/Users/apoka ...": command i expects \ followed by text
sed: 1: "install_sh=/Users/apoka ...": command i expects \ followed by text

Ironic, huh? Well taking a guess that at some point sed hadcome to depend on its own functionality to configure itself I jumped back a version… Figuring i replace BSD sed with an out of date GNU sed, and then use the old GNU sed to build the new GNU sed. Which worked great. I Installed first sed-3.0.2, and then 4.1.5 in this manner:

./configure --prefix=/usr/ --with-included-regex --with-included-gettext && make && sudo make install

I’m happy with my -r again…

# date | sed -r s/'[0-9]‘/’?'/g
Thu Apr ?? ??:??:?? PDT ????

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I keep marking this as unread in google reader…

I keep marking this as unread in google reader so that Its there when I need it… which probably means I should just blog it… automating firefox via telnet

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Daemonize Anything

I hacked together this little C program from this other little c program. Basically acts as an execution wrapper that lets you fork() and detach and run a command in the background with a pidfile and log file for program output. So far I havent had any problems with it… but then I’m not a true C guy so any input is welcomed.

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-v is for verbose, damnit

So, the vast majority of every day administrative command line utilities for Linux use -v as the switch for verbose…. when you use -v you EXPECT verbose. Well sometimes you get that one package which just CANNOT follow the rules. Someone has to think outside the box, someone has to be a unique snowflake. That someone should not be a mass process killing utility! whoever thought up that the argument -v to pkill should INVERT THE MATCH should really take a long slow look at how important being unique really is… because if you’re not aware of this, and you run something like pkill -9 -v nagios…. as root… it’s not going to do what you expect. Nothing good comes of that command.

This has been a PSA

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It’s good for the server. It’s good for the soul.

ack (http://petdance.com/ack/), love it (thanks nikolay)

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colorizing php cli scripts

It’s pretty common in most scripting languages which center around the command line (bash, perl, etc) to find information on colorizing your shell script output, mainly because those languages are tied very tightly to command line use. It can be difficult, however, to find information about adding this same nice feature to a php cli script. The reason is simple: most people dont use php for cli applications; most cli programmers use something else. It’s not difficult to adapt the same techniques listed in most bash howtos (generally in the section reserved for colorizing your command prompt) for generating colored terminal output for php.

echo "\033[31mred\033[37m\r\n";

echo "\033[32mgreen\033[37m\r\n";

echo "\033[41;30mblack on red\033[40;37m\r\n";

Simple, functional, useful (even if a bit complicated.) I leave it to you to lookup a bash prompt colorization howto to hunt down your own list of escape color codes (call it homework.)

Cheers

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