Writing some bash scripts that parse command lines, I wrote this handy template with getopt. It is easy to apply even for simplest scripts.

OPTION_SPEC="help,flag1,flag2_params:"
PARSED_OPTIONS=$(getopt -n "$0" -a -o h --long $OPTION_SPEC -- "$@")
OPTIONS_RET=$?
eval set -- "$PARSED_OPTIONS"


Parsing error or no flags

if [ $OPTIONS_RET -ne 0 ] || [ $# -le 0 ]; then
  usage;
  die;
fi

while [ $# -ge 1 ]; do
  case $1 in
    --help | -h )  usage; die;;
    --flag1 )  FLAG1=1;;
    --flag2_params )  shift; FLAG2_PARAMS="$1";;
    -- ) shift;;
    * ) echo "ERROR: unknown flag $1"; usage; die;;
  esac
  shift
done

No more unannotated $ns in my scripts!

I recently had to hack a small shell script that would read files in a directory structure generated based on the date, something like 2007/08/16. The trick was that the script would look at yesterday’s file or files generated a few days ago.

A quick search on info and here’s the magic command

FILE="...$(date -d 'yesterday' +%Y/%m/%d)"

Interestingly, you can also use things like 3 days ago, next Monday, 2 months etc. Cool!

How to (approximately) generate a top-N items list without counting the number of occurrences of all instances? Two interesting papers I found on the topic: http://citeseer.ist.psu.edu/charikar02finding.html and http://citeseer.ist.psu.edu/jin03dynamically.html. I also somebody’s seminar powerpoint presentation explaining it.

While playing with OSX I was wondering how to find out all the networks connections a particular process owns. On Linux I’d use netstat -p for this, which does not work on OSX.

It turns out that the solution is quite simple – lsof -i does the job and works on both Linux and OSX. Two other useful commands:

lsof -ai -p PID    # all connections/sockets owned by PID
lsof -i:PORT       # lists all connections/sockets with a particular PORT.

Interesting link on surviving traffic storms with WordPress: not that I currently need it, but maybe in the future…

In a nutshell:

1. fine tuning of Apache (adjusting #processes, keep alives and ListenBacklog to values that match your machine’s constraints).
2. fine tuning of MySQL query caching
3. installing WP-Cache plugin + adaptive switching on of WP-cache plugin (only in heavy-load condition)
4. disabling some plugins (the ones that take up a lot of resources)
5. enabling Squid caching for static content.

Having extensively used Linux before I found GUI configuration of OSX firewall somewhat lacking. In particular, I wanted to limit outgoing access to some IP addresses (but I can imagine you may want to play with other things as well).

I found that I could buy Flying Buttress which should allow me to do this, but I really don’t need a graphical ipfw frontend, especially the one I’d have to pay for All I needed was to write some ipfw rules and make them persistent.

Here’s what I did:

 mkdir /Library/StartupItems/CustomIPFWRules
 cd !$

Created a file called StatupParameters.plist containing:

{
  Description     = "Custom Tadek's IPFW Rules";
  Provides        = ("CustomIPFWRules");
  Uses            = ("Network");
}

Created a file called CustomIPFWRules (the name has to match the directory name) containing a simple shell script:

#!/bin/sh

. /etc/rc.common

case "$1" in
        start)

        ConsoleMessage "applying tadek's ipfw rules"
        ipfw add 2045 deny tcp from any to "ip_I_want_to_block" out
        ;;
esac

exit 0

Voila!

BTW: a useful link on playing with Firewall in OSX.