Question

Consider the following regular expression meta operators:

( ) [ ] { } . * + ? ^ $ | \

For each of the following, give one example of strings which the regular expression would match.

Describe (colloquially, in a manner that a non-technical person would understand) the set of strings that the pattern is designed to match.

Each regular expression is enclosed in the pair of '/' characters below.

[2 marks each]

(a) /^[a-z][0-9]*\.$/

(b) /([0-9]+)\s\w+\s\1/

Answer 1

ANSWER:

a.)

• Given expession: /^[a-z][0-9]*\.$/
• Let's break down each component of this expression
• ^[a-z] : The string starts with a lower case alphabet
• [0-9]*: Followed by zero or more digits
• \.$ : Ends with a dot.
• Example : a0934.
• The string starts with a lower case alphabet , Followed by zero or more digits and ends with a dot

b.)

• Given expression: /([0-9]+)\s\w+\s\1/
• Let's break down each component of this expression
• ([0-9]+): Contains one or more digits continously. This is called group 1
• \s : Followed by one white space
• \w+ : Followed by one or more ascii letter, digit or underscore
• \s: Followed by a while space
• \1: Followed by contents of group 1, that is , one or more digits continously
• Example : 345 _s3 48238
• This string Contains one or more digits continously, Followed by one white space,  Followed by one or more ascii letter, digit or underscore, Followed by a while space and finally Followed by one or more digits continously

(OR) TRY THIS

a) Strings that start with a lower case alphabet followed by any number of optional digits

Example
d123

b) 1/more digits (number) followed by a space followed by 1/more alphabets or digits or underscores followed by a space followed by exact same number that it is starting with

Example
91509 abc 91509

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