Flags

Flags in Motoko regex provide flexibility by modifying the behavior of the regex matching process. This section covers the available flags, their purpose, and how to use them effectively.

Overview

Flags are optional parameters that can alter how the regex engine interprets and processes a pattern. They enable features such as case-insensitive matching and handling multiline inputs.

Available Flags

1. CASE_SENSITIVE

• Type: Bool

• Default: true

• Description: Determines whether the regex should consider case when matching characters.

• Behavior:

  • When caseSensitive = true: Matches are case-sensitive (default behavior).
  • When caseSensitive = false: Matches are case-insensitive, treating uppercase and lowercase letters as equivalent.

• Example:

  let regex = Regex.Regex("abc", ?{caseSensitive = false});
  assert(regex.search("ABC") == #FullMatch);
  

2. MULTILINE

• Type: Bool

• Default: false

• Description: Alters the behavior of anchors (^ and $) to match at line boundaries rather than the start or end of the entire string.

• Behavior:

  • When multiline = true:
    • ^ matches the start of any line.
    • $ matches the end of any line.
  • When multiline = false (default behavior):
    • ^ matches the beginning of the entire input.
    • $ matches the end of the entire input.

• Example:

  let regex = Regex.Regex("^abc$", ?{multiline = true});
  assert(regex.search("abc\ndef\nabc") == #FullMatch);
  

Combining Flags

You can combine flags to fine-tune the regex engine's behavior. For example:

let regex = Regex.Regex("abc", ?{caseSensitive = false; multiline = true});
assert(regex.search("ABC\ndef\nabc") == #FullMatch);

In this example:

• The pattern abc is matched regardless of case.
• The engine processes each line independently due to multiline = true.

Default Behavior Without Flags

If no flags are specified, the engine uses the following defaults:

• caseSensitive = true
• multiline = false

This means:

• Matching is case-sensitive.
• Anchors (^ and $) match only at the start and end of the entire input.

Best Practices

• Use caseSensitive = false for patterns that need to ignore case differences, such as matching user inputs in a case-insensitive manner.
• Use multiline = true when processing multi-line text, such as logs or formatted documents, where each line might have independent matching requirements.