Regular Expressions Flashcards

Programming

Share code

Regular Expressions

The basics of regular expression syntax and a few examples.

What does the regular expression $a (b ∣ c)^{*} d$ match?

Strings that start with 'a', end with 'd', and have any combination of 'b' and 'c' characters in between

What is the closure property of regular languages under union?

If L1 and L2 are regular languages, then L1 ∪ L2 is also a regular language.

What is the syntax for the Kleene star of $R$ ?

$R^{*}$

What does the regular expression $a^{*}$ match?

Any string of zero or more 'a' characters (including the empty string)

What is the syntax for a concatenation of $R_{1}$ and $R_{2}$ ?

$R_{1} R_{2}$

How is the empty string represented?

By the symbol $ϵ$

What does the regular expression $a ∣ b$ match?

Either the character 'a' or the character 'b'

What does the regular expression $ab$ match?

The string ab

What does the regular expression $(a ∣ b)^{*}$ match?

Any string composed of 'a' and 'b' characters in any order, including the empty string

What is the syntax for a choice between $R_{1}$ and $R_{2}$ ?

$R_{1} ∣ R_{2}$

Import this source into your Adalyn library to start learning with spaced repetition.