You can find a complete list of Unicode categories in the tutorial. First, a word of warning and a word of courage. This tutorial is a gentle introduction to getting you started with using regular expressions in calibre. Regular expressions are features used in many places in calibre to perform sophisticated manipulation of e-book content and metadata.
#Regular expression not equal plus
, the vertical bar or pipe symbol |, the question mark ?, the asterisk or star *, the plus sign +, the opening parenthesis (, the closing parenthesis ), the opening square bracket [, and the opening curly brace matches a single character that is not in the given Unicode category. All about using regular expressions in calibre. Twelve characters have special meanings in regular expressions: the backslash \, the caret ^, the dollar sign $, the period or dot. In a programming language, there is usually a separate function that you can call to continue searching through the string after the previous match. In a text editor, you can do so by using its “Find Next” or “Search Forward” function. Fortunately the grouping and alternation facilities provided by the regex engine are very capable, but when all else fails we can just perform a second match using a separate regular expression supported by the tool or native language of your choice. It only does so when you tell the regex engine to start searching through the string after the first match. When attempting to build a logical or operation using regular expressions, we have a few approaches to follow. If the string is Jack is a boy, it matches the a after the J. It matches the first occurrence of that character in the string. The most basic regular expression consists of a single literal character, such as a. The regex (? x ) ( egex p ? ) \? shows meta tokens in purple, grouping in green, character classes in orange, quantifiers and other special tokens in blue, and escaped characters in gray. Strings are highlighted in green.Ĭharacters with special meanings in regular expressions are highlighted in various different colors. We use the term “string” to indicate the text that the regular expression is applied to. Matches are highlighted in blue on this site. It is the most basic pattern, simply matching the literal text regex. This is actually a perfectly valid regex. On this website, regular expressions are shaded gray as regex. Im trying to define an expression that excludes exactly this text System (case insensitive), but can contain the word System providing its not just that. Text Patterns and MatchesĪ regular expression, or regex for short, is a pattern describing a certain amount of text. Im banging my head against a wall with a regular expression. This quick start explains the syntax supported by the most popular regular expression flavors. When two applications use a different implementation of regular expressions, we say that they use different “regular expression flavors”. Many applications and programming languages have their own implementation of regular expressions, often with slight and sometimes with significant differences from other implementations. Each topic in the quick start corresponds with a topic in the tutorial, so you can easily go back and forth between the two. For detailed information, consult the regular expressions tutorial. Obviously, this brief introduction cannot explain everything there is to know about regular expressions. It's not free, but it's the best regex tool out there by far- and it keeps getting better with every incremental release.This quick start gets you up to speed quickly with regular expressions. Unfortunately, JavaScript doesn't support negative lookbehind, so if you want to test that one, I recommend RegexBuddy. You can test this regex in the cool online JavaScript Regex evaluator. To avoid incompatibility, we can restate our solution using negative lookahead: And those that do typically have severe restrictions on the lookbehind, eg, it must be a simple fixed-length expression. One easy way to exclude text from a match is negative lookbehind:īut not all regex flavors support negative lookbehind. Stating a regex in terms of what you don't want to match is a bit harder. It's easy to formulate a regex using what you want to match. Regular expressions are great at matching. The quick brown jumped over the lazy dog. and I used a regular expression of (which I know is incorrect) (why this doesn't work I don't understand it would make life SO much easier), then the returned search results would be: The quick brown fox jumped over the lazy dog. The regular expression should find and return everything EXCEPT the text string in the search expression.įor example, if the word fox was what I wanted to exclude, and the searched text was: I am trying to find a way to exclude an entire word from a regular expression search. equivalent to those generated by regular expressions ¾Given any regular expression R, there exists a finite state automata M such that L(M) L(R) see Problems 9 and 10 for an indication of why this is true. I seem to have stumbled upon a puzzle that evidently is not new, but for which no (simple) solution has yet been found. Excluding Matches With Regular Expressions