Exercises
Last updated on 2023-05-03 | Edit this page
Overview
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?
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?
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?
^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)?
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?
\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?
0+[a-z]{4}\b
How do you match any 4-digit string anywhere?
\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?
\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?
\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?
.* : .*, \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.
- Regular expressions answers