Most regular expression engines discussed in this tutorial support the following four matching modes:

Specifying Modes Inside The Regular Expression

You can specify these modes within a regex using mode modifiers. For example:

• (?i) turns on case-insensitive matching.

• (?s) enables single-line mode.

• (?m) enables multi-line mode.

• (?x) enables free-spacing mode.

Example:

(?i)hello matches "HELLO"

Turning Modes On and Off for Only Part of the Regex

Modern regex flavors allow you to apply modifiers to specific parts of the regex:

• (?i-sm) turns on case-insensitive mode while turning off single-line and multi-line modes.

To apply a modifier to only a part of the regex, you can use the following syntax:

(?i)word(?-i)Word

This pattern makes "word" case-insensitive but "Word" case-sensitive.

Modifier Spans

Modifier spans apply modes to a specific section of the regex:

• (?i:word) makes "word" case-insensitive.

• (?i:case)(?-i:sensitive) applies mixed modes within the regex.

Example:

(?i:ignorecase)(?-i:casesensitive)

Summary

Understanding matching modes is essential for writing efficient and accurate regex patterns. By leveraging modes like case-insensitivity, single-line, multi-line, and free-spacing, you can create more flexible and maintainable regular expressions.