Wednesday, July 30, 2008

Pondus: A personal weight management software

A week after my return from a New England & Canada cruise, I found myself busy searching for a personal weight management software.

Why weight management? See the chocolate dessert buffet pictures taken on board the Holland America Maasdam cruise ship.

I came across pondus, a python program that is free and open-sourced.

Pondus has a rather modest feature set: the ability to enter one's weight over time, and have it plotted in a chart. It does not have too many bells and whistles, but it is very simple to use.

Pondus is packaged with certain Debian releases (namely, Lenny and Sid). So a simple apt-get install pondus will put it on your system. Because I run Debian Etch, I need to install it from source files.

I downloaded the source tar ball as well as the install instructions from here. The instructions are straight-forward, and I installed pondus without a glitch.

To run pondus, just type pondus in the command line. When you run pondus for the first time, it is not too terribly exciting .... because you have not entered any weight data.

Before you enter your weight, you should customize the unit of measure that pondus will use(lbs versus kgs). Click on the Tool icon (the one with the screwdriver and wrench) to bring up Preferences. For me, I prefer pounds (that is the unit my scale uses).

Now, let's enter some weight data, and draw a pretty chart.

To enter a weight, click on the Plus icon.

To plot the data, click on the Chart icon.

Pondus has some additional useful features such as data import and export in CSV format, as well as the ability to save the chart in png or svg (2-dimensional vector graphics) format.

An interesting feature is that you can set time-sensitive goals (aka, Weight Planner). For example, you can set a goal such as "weigh 180 lbs on August 15". This feature is disabled by default. To enable it, bring up Preferences as above, and click Use Weight Planner checkbox to select it, and choose whether to include the weight plan in your plots. Note that this feature is not for everyone (do I really need yet another remainder of my shortcomings?)

Pondus is adequate for tracking my body weight. I'm still searching for software that can also track my blood pressure. Won't it be perfect if a single software can manage both weight and blood pressure?

Monday, July 28, 2008

How to do reverse DNS lookup

Most people can better remember domain names, e.g.,, than their corresponding IP addresses, (In this example, is the home of the Free Software Foundation.) We delegate the responsibility to machines, aka, the DNS servers, to resolve the domain names for us.

Sometimes, we do need to manually lookup the IP address of a domain name. You may already be familiar with the nslookup command which is now deprecated. We use the dig command to make DNS queries.
 $ dig +noall +answer 67 IN CNAME 67 IN A

The IP address is displayed in the A record, and is

The +noall, +answer combination basically tells dig to only report the answer of the DNS query and skip the rest of the output.

You can also use the dig command with the -x option to do a reverse DNS lookup. A reverse DNS lookup means you want to look up the domain and host name of an IP address.

 $ dig +noall +answer -x 36000 IN CNAME 300 IN PTR

The PTR record is the one that contains the domain host name. The domain name is, as you expect,

Note that PTR records are not required for IP addresses. If a PTR record is not defined for an IP address, you cannot do a remote DNS lookup.

Friday, July 18, 2008

How to count number of files in a directory

Now that I am back from vacation, I had to take care of some chores, like uploading the pictures taken with my digital camera.

I stepped out during the long upload process (400+ pictures). When I returned, it was already done. To just make sure all pictures are now on the server, I wanted to count the number of files in the targetdir directory.

$ ls -1 targetdir | wc -l

The above command reads ls dash one piped to wc dash letter l.

Note that if you had used ls dash letter l instead, the count is one greater than the actual number of files. This is because ls dash letter l outputs an extra total line:

$ ls -1 targetdir 
total 529436
-rw-r--r-- 1 peter peter  1510976 Jul 13  2008 DSCN1001.jpg

The above method will count symbolic links as well as subdirectories in targetdir (but not recursively into subdirectories).

If you want to exclude subdirectories, you need a heavier duty tool than ls.

$ find targetdir -maxdepth 1 -type f | wc -l

-type f ensures that the find command only returns regular files for counting (no subdirectories).

By default, the find command traverses into subdirectories for searching. -maxdepth 1 prevents find from traversing into subdirectories. If you do want to count files in the subdirectories, just remove -maxdepth 1 from the command line.

Note that the find command does NOT classify a symbolic link as a regular file. Therefore, the above find -type f command does not return symbolic links. As a result, the final count excludes all symbolic links.

To include symbolic links, add the -follow option to find.

$ find targetdir -follow  -maxdepth 1 -type f | wc -l