Regular Expressions

TODO

• https://en.wikipedia.org/wiki/Regular_expression
• https://en.wikipedia.org/wiki/Raku_rules

Introduction

I found Regular-Expressions.info very useful to me, from now on I go there if I am not sure how exactly the thing works.

You don’t need to reinvent the wheel every time. There are “community patterns” on regexr.com, that solves your problem, or at least usually give you a nice baseline.

Optional item ‘?’

Makes the preceding token in optional. regexp? will match regex and regexp. In order to make optional more tokens use grouping, e.g. Reg(ular)? ?Ex(p?ressions)?.

• Optional Items (regular-expressions.info)

Character Classes or Character Sets ‘[]’

• Character Classes or Character Sets (regular-expressions.info)

Regex Alternation ‘|’

Alternation has the lowest precedence of all regex operators. So the regex math either everything to the left from this sign | or everything to the right. In case the alternation should be applied only as a part of the pattern, then it needs to be closed with braces to create a group.

/first_pattern|second_pattern/

It is equivalent to

/(first_pattern|second_pattern)/

and not equivalent to

/first_patter(n|s)econd_pattern/

• Alternation (regular-expressions info)

Metacharacter

• Word Boundaries (regular-expressions.info)

Integer

anywhere on the line

$pattern = '/[[:digit:]]+/';

Tousand dot every third position from end

$integer = '/[[:digit:]]{1,3}(\.[[:digit:]]{3})*/';

Tousand - dot every third position from end, ,-

$pattern = '/[[:digit:]]{1,3}(\.[[:digit:]]{3})*(\ )*,-/';

Float

Tousand dot every third position from end with comma

$float = '/([[:digit:]]){1,3}(\.[[:digit:]]{3})*(,[[:digit:]]*)?/';

Tousand dot every third position from end with comma and Kč

$pattern = '/([[:digit:]]){1,3}(\.[[:digit:]]{3})*(,[[:digit:]]*)?(\ )*Kč/';

Tousand dot every third position from end with comma and CZK

$pattern = '/([[:digit:]]){1,3}(\.[[:digit:]]{3})*(,[[:digit:]]*)?(\ )*CZK/';

CZK and tousand dot every third position from end with comma

$pattern = '/CZK(\ )*([[:digit:]]){1,3}(\.[[:digit:]]{3})*(,[[:digit:]]*)?/';

CZK at start or end and tousand dot every third position from end with comma

$pattern = '/(([[:digit:]]){1,3}(\.[[:digit:]]{3})*(,[[:digit:]]*)?(\ )*CZK|CZK(\ )*([[:digit:]]){1,3}(\.[[:digit:]]{3})*(,[[:digit:]]*)?)/';