Below we use the correct expression to ignore the result of the “ei” check when a “c” appears in front of it: Command the food taster to have a nibble, and see what happens. We need to be able to “look around” without consuming. The above solution looks good at first, but then the last three of the renegade spellings has captured the “s”, “v” and “w” - which are not in themselves problem letters, but they matched with the negated metacharacter. If we just apply two simple searches for the two sets of offending exceptions, it won’t work as you can see here:Ĭlearly, the search can’t tell if it’s looking at a good “cei” or it has found a genuine rule-breaking “ei”.Īt least applying the second pattern is straightforward for catching half the offenders that contain “cie”:īut how can we detect both sets of offenders correctly with just one query? The answer would seem to be that we can use an alternation (an “either-or” rule) to combine both rules and then disallow the “c” when checking for the “ei” rule: How can you find letter combinations that break the rule “i before e except after c”? This familiar but rather unfortunate rule of English language has a lot of exceptions.

Here is an example that shows the food taster dilemma in detail. We used this to find the first word in a line of Shakespearean text: They were used to clamp the search to the beginning or end of a line.

This is why paranoid kings and emperors employed food tasters you couldn’t un-eat an apple after you discovered it was poisoned.īut if you remember, when we saw anchors we noticed they didn’t consume. This sounds like the right thing to do, but it does mean you can’t check actions before you commit to them. When the regex process matches successfully, it includes the matched character in the result and then moves on to the next character. You’ll soon appreciate why I didn’t cover this in the first post. But first, we have to understand consumption.

This time I’m going for the next step up in difficulty: the lookaround functions. By knowing one way to search through text (even a 70-year-old way) in a computational style, we can not only solve problems with different tools, we can also better understand the problems with search itself. Just a reminder of why we should value regular expressions. Things were fairly simple to comprehend, and all was good with the world. In my previous regex post, we covered simple regular expressions that work with most code base libraries, as well as with the search functions in many editors.

Finding hidden text in microsoft word