How important is knowing Regexs?

Question

My personal experience is that regexs solve problems that can\'t be efficiently solved any other way, and are so frequently required in a world where strings are as important as

Answer 1

I have really mixed feelings. I have used them and know the bones of the syntax and something in me loves their conciseness. However they are not commonly understood and are a highly obfuscated form of code. I too would like to see performance comparisons against similar operations in plain code. There is no question that the exploded code will be more maintainable and more easily and widely understood, which is a serious consideration in any commercial software project.

Even if they turn out to be more performant, the argument for them taken to its logical conclusion would see us all embedding assembler into our code for important loops - perhaps we should. Neat and concise and very fast, but almost un-maintainable.

On balance I think that until the regex syntax becomes mainstream they probably cause more trouble than they solve and should be used only very carefully.

Answer 2

I agree with pretty much everything said here, and just need to include the mandatory quip:

Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems.

(attributed to Jamie Zawinski)

Like most jokes, it contains a kernel of truth.

Answer 3

There are some tasks where regular expressions are the best tool to use.
There are some tasks where regular expressions are pointlessly obscure.
There are some tasks where they're reasonably appropriate, but a different approach may be more readable.

In general, I think of using a regular expression when an actual pattern is involved. If you're just looking for a specific string, I wouldn't generally use a regex. As an example of a grey area, someone once asked on a newsgroup the best way to check whether one string contained any of a number of other strings. The two ways which came up were:

• Build a regex with alternatives and perform a single match.
• Test each string in turn with string.Contains.

Personally I think the latter way is much simpler - it doesn't require any thought about escaping the strings you're looking for, or any other knowledge of regular expressions (and their different flavours across different platforms).

As an example of somewhere that regular expressions are quite clearly the wrong choice, someone seriously proposed using a regular expression to test whether or not a string three characters long. Their regular expression didn't even work, despite them claiming that the reason they thought of regular expressions first is because they'd been using them for so long, and that they naturally sort of "thought" in regular expressions.

There are, however, plenty of examples where regular expressions really do make life easier - as I say, when you're actually matching patterns: "I want one letter, then three digits, then another letter" or whatever. I don't find myself using regular expressions very often, but when I do use them, they save a lot of work.

In short, I believe it's good to know regular expressions - but equally to be careful about when to use them. It's easy to end up with write-only code which could be made simpler to understand by rewriting with simple string operations, even if the resulting code is slightly longer.

EDIT: In response to the edit of the question...

I don't think it's a good idea to be evangelical about them - in my experience, that tends to lead to using them where an alternative would be simpler, and that just makes you look bad. On the other hand, if you come across someone writing complicated code to avoid using a regular expression, it's fine to point out that a regex would make the code simpler.

Personally I like to comment my regular expressions in quite a detailed way, splitting them up onto several lines with a comment between each line. That way they're easier to maintain, and it doesn't look like you're just trying to be "hard core" geeky (which can be the impression, even if it's not the actual intended aim).

I think the most important thing is to remember that short != readable. Never claim that using a regex is better because it requires less code - claim that it's better when it's genuinely simpler and easier to understand (or where there's a significant performance benefit, of course).

Answer 4

I find that regex's can be very helpful depending on the type of programming that you do. However I probably write less than one regex a month, and because of this long interval between requiring regex's I forget alot about how they work.

I should probably go through mastering regular expressions or something similar someday.

Answer 5

I find it very useful to know regular expressions. They are a very powerful tool, and in my opinion there are problems that you simply can't solve without these.

I would however not take regular expressions as a killing criterion for "hiring you as a senior programmer". They are like the wealth of other tools in the world. You should really known them in a problem domain where you need them, but you cannot presume that someone already knows all of these.

"a junior is always allowed the leeway of training"

If a senior isn't, then I would not hire him!

To the ones that argue how complex and unreadable a regular expression is: If the regexp solution to a problem is complex and unreadable, then probably the problem itself is! Good luck in solving it in an other way...

Answer 6

Knowing when to use a regexp and the basics of how they work and what their limitations are is important. But filling your head with a lot of syntax rules that you probably won't need very often is just a pointless academic exercise.

A regexp crib sheet can be written on one sheet of A4 paper or a couple of pages in a textbook - no need to know this stuff by heart, If you use it every day it will stick. If you don't use it very often then the brain cells are probably better used for something else.