Overview

Teaching: 0 min
Exercises: 50 min

Questions

• How do you find and match strings with regular expressions?

Objectives

• Test knowledge of use of regular expressions

Exercises

The exercises are designed to embed the regex knowledge you learned during this module. We recommend you work through it sometime after class (within a week or so).

What does Fr[ea]nc[eh] match?

Answer

This matches France, French, in addition to the misspellings Frence, and Franch. It would also find strings where there were characters to either side of the pattern such as France's, in French, or French-fried.

What does Fr[ea]nc[eh]$ match?

Answer

This matches France, French, Frence, and Franch only at the end of a line. It would also match strings with other characters appearing before the pattern, such as in French or Sino-French.

What would match the strings French and France only that appear at the beginning of a line?

Answer

^France|^French This would also find strings with other characters coming after French, such as Frenchness or France's economy.

How do you match the whole words colour and color (case insensitive)?

Answer

In real life, you should only come across the case insensitive variations colour, color, Colour, Color, COLOUR, and COLOR (rather than, say, coLour. So one option would be \b[Cc]olou?r\b|\bCOLOU?R\b. This can, however, get quickly quite complex. An option we’ve not discussed is to take advantage of the / delimiters and add an ignore case flag: so /colou?r/i will match all case insensitive variants of colour and color.

How would you find the whole-word headrest or head rest but not head  rest (that is, with two spaces between head and rest?

Answer

\bhead ?rest\b. Note that although \bhead\s?rest\b does work, it would also match zero or one tabs or newline characters between head and rest. In most real world cases it should, however, be fine.

How would you find a 4-letter word that ends a string and is preceded by at least one zero?

Answer

0+[a-z]{4}\b

How do you match any 4-digit string anywhere?

Answer

\d{4}. Note this will match 4 digit strings only but will find them within longer strings of numbers.

How would you match the date format dd-MM-yyyy?

Answer

\b\d{2}-\d{2}-\d{4}\b In most real world situations, you are likely to want word bounding here (but it may depend on your data).

How would you match the date format dd-MM-yyyy or dd-MM-yy at the end of a line only?

Answer

\d{2}-\d{2}-\d{2,4}$

How would you match publication formats such as British Library : London, 2015 and Manchester University Press: Manchester, 1999?

Answer

.* : .*, \d{4} You will find that this matches any text you put before British or Manchester. In this case, this regular expression does a good job on the first look up and may be need to be refined on a second depending on your real world application.

Key Points

• Regular expressions answers