Sed - reducing effort since '74

Sed, short for 'stream editor', is a (pretty awesome) utility created by  Lee E. McMahon of Bell Labs. I would like to take a detour here and mention that I am in real awe of Bell labs. They have given us so much, starting from C and C++ to Unix itself. Another useful utility (which I should cover here soon) made by them is cscope.

Now, coming back to 'sed', it saved me quite some effort today while working with Kate. Well, frankly, the time it took me to learn some basic tricks and perfect the command might have taken a little longer than it would have taken me to manually make the change, but I won't add that time. Why ? Because the time invested would save me plenty more in the future, whereas doing the task manually wouldn't save me anything in the future.

So what was this task ? As I have explained here, I am working on the modeline variable editor in Kate. The widget that my mentor and I had created, to be used in place of the 'QLineEdit' , had some help text. I had forgotten to wrap the text in i18n() wrappers.

The initial text was something like this :-

item-> setHelpText(" Help text goes here ") ;

Now had there been just two or three of such occurrences, I wouldn't have thought about using sed; but there were a lot more (I didn't check then, but as it turns out, about 40 changes were made using sed). Anyways, I needed the text to be modified to :-

item->setHelpText(i18n(" Help text goes here"));

With sed, that wasn't too hard.

sed 's:setHelpText(\"\([a-zA-Z0-9.() ]*\)\"):setHelpText(i18n(\"\1\")):g' <old >new

Just one line and all the changes were made. And I had with me another patch to offer to the community ;-).

Combined with Regular Expression (Regex), sed has a lot to offer.

Suggested links :

For more information on Internalization (i18n), check out the Wikipedia page.
For a tutorial on Sed, I would suggest this.
Online manual for Sed is available here.

Kate's Variable Editor

Well, as I have mentioned before, I am part of 'Season of KDE' this year and am working on Kate. My project statement is to create a 'Modeline Editor'.

Frankly speaking, modeline variables is a feature that I was unaware of before I read about this project.  It is one of those subtle features that can make editing and formatting very easy. With just a line at the beginning (or end) of the file you can tell the editor things about tab-width, syntax-highlighting, background-color and what not.

With a lot of assistance from my mentor, Dominik Haumann, we began working on the variable editor by creating a new 'widget'. For now, this remains independent of the rest of the Kate but once it is ready (which it almost is), we'd merge it.

Some important lessons learnt during the process that I'd like to share :-

1. Make use of version control :- After spending about 24 hours on a part of the project, I e-mailed my mentor the new source code; only to learn that those very changes had already been made. So how did I miss it ? I thought I was smart enough to update my working copy in the beginning of those 24 hours, but not once during those working hours did I bother to check if some changes had been made. That was one valuable lesson. As Vicky correctly pointed out though, there was a silver lining : I wrote some code that was written by a more experienced person as well; I had the opportunity to compare and learn. 
2. Develop complex widgets separately : As I mentioned above, the variable editor is being developed as a widget separately. It required a combination of combo-boxes to cater for boolean, integer, colors, fonts and other strings. The development of widget 'within' the editor would have made it harder. With only this segment to focus on, we can forget about the rest of the editor and develop and test the variable-editor. Here are some snapshots of the widget :-

Here you can see the combo-boxes for boolean and color values
Spin box for integer

The color combo and the line-edit for string values.

The color combo-box (KColorCombo)

The font combo-box (KFontCombo)

Yet another integer spin button and color-combo.

Soon, this widget would be a part of the Kate text editor.

Software projects and 'grep'

It might sound as weird title, especially when I emphasize that by 'software project' I refer to absolutely 'any' project. After a few days of trying to understand the source code of a few projects (including Kate), I have come to realize that it is hard to understand the entire code at once.

Realizing the impossibility of understanding the entire code-base (which could be well over a hundred thousand lines) I started trying other means. The first step was to identify the 'main' file. As I am working with C/C++, this file is easy to identify as it is the one containing the function :-

int main (int argc, char *argv[] ) 

Knowing what I am looking for, this simple command (or a few variations) allow me to spot the file where it all begins :-

grep "int main" * -R 

As should be clear, this would search the source code directory 'recursively' to find me the file with the keywords. At this point, I would like to highlight why it would be easy to maintain a program that called the 'first' function by the name 'main'. Whichever language it is written in, use of this convention can make it easier to maintain. 

Once the main file has been spotted, I proceed to find the functions in almost a similar fashion. This saves me the effort of going through pieces of code that are rarely (or at times never) used. I can follow the 'flow of program' more easily and I know which function lies where. As and when I proceed to understand the functions, I try to make certain notes about the functions, in the form of comments. These notes could be something describing the task of the function, or could point to some other piece of information, or at times hints for improving the function later.

'grep' has proved very useful to me, and although I am not very good with RegEx (regular expressions), I now plan to get hold of them so as to be able to use them to spot what I want in combination with 'egrep'.

 

Season of KDE (SoK)

Well, this is my first post regarding the Season of KDE 2011. On advice from the mentors, I have decided to put up my progress on the project on this blog. I realize this would be a good exercise, as over the years the single most important thing that I have learnt is that explaining difficult things to others, only makes my own understanding better.

With that selfish motive hidden deep inside, I look forward to an exciting experience writing about my progress. Starting from the difficulties to the work-arounds, I plan to post about it all.

Hope you enjoy reading it as much.