Contents

  Icon

Mode modifiers

Anchors

Basic metacharacters

Character classes

Comments

Control and code

Grouping

Look around

Mode modifiers

Quantifiers

Specific characters

Usually match modes, e.g. whether the match should be case-insensitive or not, are set outside of the regular expression. Mode modifiers allow you to set them inside and for parts of an expression.

bullet Basic structure

bullet Mode modifiers

Basic structure

 

Item

 

Meaning:

 
 

(?M)

 

Turn modifier M on for the rest of the expression or until it is turned off.

 
 

(?-M)

 

Turn modifier M off for the rest of the expression or until it is turned on.

 
 

(?M:…)

 

Turn modifier M on for the expression between the non capturing parentheses.
(Note: the modifier is followed by colon.)

 
 

In the table “…” stands for any one or more characters.

 

Mode modifiers

 

Item

 

Mode:

 
 

i

 

Case-insensitive mode.

 
 

m

 

Multiline mode
Allow ^ and $ to match at embedded newlines.

 
 

s

 

Dot matches all mode.
Dot (.) will match any character including newline.

 
 

x

 

Free flow mode.
Ignores (most) whitespace and permits comments preceded by “#” in an expression.

 
 

You can combine multiple modifiers, turning some on and some of. For example (?i-m) will turn case-insensitivity on and multiline mode off.