text_parser

Pub Version Dart CI

A Dart package for parsing text flexibly according to preset or custom regular expression patterns.

Usage

Using preset matchers (URL / email address / phone number)

If matchers is omitted in TextParser, the three preset matchers (UrlMatcher, EmailMatcher and TelMatcher) are used automatically.

The default regular expression pattern of each of them is not very strict. If it is unsuitable for your use case, overwrite the pattern by yourself, referring to the description in a later section of this document.

import 'package:text_parser/text_parser.dart';

Future<void> main() async {
  final parser = TextParser();
  final elements = await parser.parse(
    'abc https://example.com/sample.jpg. def\n'
    'foo@example.com +1-012-3456-7890',
  );
  elements.forEach(print);
}

Output:

matcherType: TextMatcher, text: abc , groups: []
matcherType: UrlMatcher, text: https://example.com/sample.jpg, groups: []
matcherType: TextMatcher, text: . def\n, groups: []
matcherType: EmailMatcher, text: foo@example.com, groups: []
matcherType: TextMatcher, text:  , groups: []
matcherType: TelMatcher, text: +1-012-3456-7890, groups: []

Overwriting the pattern of a preset matcher

If you want to parse only URLs and phone numbers, but treat only a sequence of eleven numbers after "tel:" as a phone number:

final parser = TextParser(
  matchers: const [
    UrlMatcher(),
    TelMatcher(r'(?<=tel:)\d{11}'),
  ],
);

If the match patterns of multiple matchers have matched the same string at the same position in text, the first matcher is used for parsing the element.

Using a custom matcher

You can create a custom matcher easily by extending TextMatcher. The following is a matcher for links of the Markdown format like [text](link_such_as_url_or_path).

class MdLinkMatcher extends TextMatcher {
  const MdLinkMatcher() : super(r'\[(.+?)\]\((.+?)\)');
}

...

final parser = TextParser(
  matchers: const [MdLinkMatcher()],
);
final elements = await parser.parse('abcde[foo](bar)fghij');
elements.forEach(print);

Output:

matcherType: TextMatcher, text: abcde, groups: []
matcherType: MdLinkMatcher, text: [foo](bar), groups: [foo, bar]
matcherType: TextMatcher, text: fghij, groups: []

Groups

Each TextElement in a parse result has the property of groups. It is an array of strings that have matched the smaller pattern inside every set of parentheses ( ).

To give the above code as an example, there are two sets of parentheses in the above example; (.+?) in \[(.+?)\] and \((.+?)\). They match "foo" and "bar" respectively, so they are added to the array in that order.

Tip:

If you want certain parentheses to be not captured as a group, add ?: after the starting parenthesis, like (?:pattern) instead of (pattern).

Limitations

  • Parsing is not executed in an isolate but in the main thread on the web, which dart:isolate does not support.
  • It may take seconds to parse a very long string with multiple complex match patterns.

Troubleshooting

Positive lookbehind sometimes does not work.

e.g.

  • Text to be parsed
    • '123abc456'
  • Match pattern 1
    • r'\d+'
      • Any sequence of numeric values
  • Match pattern 2
    • r'(?<=\d)[a-z]+'
      • Alphabets after a number

In the above example, you may expect the first match to be "123" and the next match to be "abc", but the second match is actually "456".

This is due to the mechanism of this package that excludes already searched parts of text in later search iterations; "123" is found in the first iteration, and then the next iteration is targeted at "abc456", which does not match (?<=\d).

An easy solution is to add ^ to the positive lookbehind condition, like (?<=\d|^).

Libraries

text_parser