rex v1.2.0

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Friendly Regular Expressions

A friendly interface for the construction of regular expressions.

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Rex

Build Status codecov.io Lifecycle: stable

Friendly Regular Expressions

Regular expressions are very powerful feature, however they are often difficult to interpret. Rex allows you to build complex regular expressions from human readable expressions. So instead of writing (and later trying to decipher)

r <- "^(?:(((?:[^:])+)://))?((?:(?:(?!:/).)*)+)(?:(:([[:digit:]]+)))?(?:(/.*))?$"

You can write

r <- rex(

  start,

  ## match the protocol -- may exist or may not
  maybe(capture(
      capture(except_some_of(":")),
      "://"
      )),

  ## match the path
  capture(one_or_more(not(":/"))),

  ## get the port
  maybe(capture(":", capture(numbers))),

  ## and the rest
  maybe(capture("/", anything)),

  end

)

While these expressions are a big longer than their corresponding regular expression, they are much more readable and maintainable.

Installation

install.packages("rex")

Usage

The vignettes have longer form usage examples.

Each rex() function call can include a number of functions and shortcuts. For a full list of the functions available please see ?rex and ?shortcuts.

Rex Mode

Rex functions are not exported because they are only useful within rex() calls, but they can be temporarily attached using rex_mode() which allows them to be auto-completed.

Using Rex in other packages

Using rex in other packages will generate spurious NOTEs from R CMD check unless you include a call to rex::register_shortcuts() with your package name somewhere in your package source. This function registers all of the rex shortcuts as valid variables fixing the NOTEs.

See Also

  • Regularity - Ruby library that partially inspired rex.
  • PCRE - Perl Compatible Regular Expressions, the engine that rex regular expressions use.
  • Perl 5 Regular Expressions - Perl regular expression documentation, which are nearly 100% compatible with PCRE.

Functions in rex

Name Description
counts Counts
as.regex Coerce objects to a regex.
not Do not match
group Create a grouped expression
%or% Or
lookarounds Lookarounds
escape Escape characters for a regex
capture Create a capture group
character_class Create character classes
character_class_escape Character class escapes
shortcuts Shortcuts
wildcards Wildcards
register_shortcuts Register the Rex shortcuts
as.character.regex Regular Expression
rex Generate a regular expression.
rex_mode Toggles rex mode.
re_matches Match function
re_substitutes Substitute regular expressions in a string with another string.
single_shortcuts Single shortcuts
No Results!

Vignettes of rex

Name
NASA.txt
log_parsing.Rmd
stackoverflow.R
url_parsing.Rmd
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Last month downloads

Details

Type Package
URL https://github.com/kevinushey/rex
BugReports https://github.com/kevinushey/rex/issues
License MIT + file LICENSE
VignetteBuilder knitr
Collate 'aaa.R' 'utils.R' 'escape.R' 'capture.R' 'character_class.R' 'counts.R' 'lookarounds.R' 'match.R' 'or.R' 'rex-mode.R' 'rex.R' 'shortcuts.R' 'wildcards.R' 'zzz.R'
RoxygenNote 7.1.0
NeedsCompilation no
Packaged 2020-04-21 17:14:58 UTC; jhester
Repository CRAN
Date/Publication 2020-04-21 18:20:06 UTC

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