in Perl, regular expressions

regular expressions saved my life

A little note to all those programmers who have not taken the time to learn how to use regular expressions: DO IT NOW. I think learning Perl and regular expressions while I was working at Cisco was almost the best thing I took from that job. You never realise how useful it is to know until the day you are presented with a rather large text file and you have to extract some of the data. This is what happened to me last week; and it ain’t the first time either.

The file I was looking at was around 250 lines long and consisted of three tab separated numbers on each line, of which I was interested in only one of these numbers at a time. The idea was that I was trying to generate an array in Java initalised with these numbers, e.g:

int [] = {2,3,4,5,7,8,8,2,3............}

For the record this was just for some testing I was doing. Anyway, doing this without regular expressions would have been a nightmare, as not only did each file have 250 lines but there was 5 files. Instead 5 lines of Perl:

my $ar = "{";
while($text =~ /^\s*(\d+)\s+(\d+)\s+(\d+)\s*$/gm) {
    $ar .=  "$2,";}
chop $ar;
$ar .= "}";

done it in a flash. Now what to those people who do not know how to use regular expressions do in this situation?

They should teach more people this kind of programming at university. I’m all for learning the theory behind things, but there does have to be a better theory/practical split in my opinion. Maybe even a course called “Practical Computer Programming”, where they teach things like regular expressions, debugging, memory management (yes even for Java programmers), design patterns, useful data structures, etc. If anyone wants to pay me a tidy sum to teach it then your wish would be my command 🙂

Write a Comment