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ExpressionEngine University. Tutorials, Tips, Tricks and more! Join us at ExpressionEngine University, a place to learn and share new knowledge based around building stuff with ExpressionEngine CMS! The ExpressionEngine Forums are a great place to get involved if you have questions, or to share your own knowledge in order to help others. Welcome back to the Blue Fish ExpressionEngine Tutorial - Create a blog series. Part 3 is about publishing entries. Before we begin, if you haven't read Part 1: Installation, you can do so here and Part 2: Channel Fields, Categories, Channels, you can do so here. Popular CMS’ such as WordPress and ExpressionEngine have many free or premium templates available online that can reduce the cost of and help you customize your system. This is the typical layout of a WYSIWYG editor, which has features that are standard in word processors today, such as bolding, italicizing and justifying paragraphs.

This quick start gets you up to speed quickly with regular expressions. Obviously, this brief introduction cannot explain everything there is to know about regular expressions. For detailed information, consult the regular expressions tutorial. Each topic in the quick start corresponds with a topic in the tutorial, so you can easily go back and forth between the two.

Many applications and programming languages have their own implementation of regular expressions, often with slight and sometimes with significant differences from other implementations. When two applications use a different implementation of regular expressions, we say that they use different “regular expression flavors”. This quick start explains the syntax supported by the most popular regular expression flavors.

Text Patterns and Matches

A regular expression, or regex for short, is a pattern describing a certain amount of text. On this website, regular expressions are highlighted in red as regex. This is actually a perfectly valid regex. It is the most basic pattern, simply matching the literal text regex. Matches are highlighted in blue on this site. We use the term “string” to indicate the text that the regular expression is applied to. Strings are highlighted in green.

Characters with special meanings in regular expressions are highlighted in various different colors. The regex ([Rr]egexp?)? shows meta tokens in purple, grouping in green, character classes in orange, quantifiers and other special tokens in blue, and escaped characters in gray.

Literal Characters

The most basic regular expression consists of a single literal character, such as a. It matches the first occurrence of that character in the string. If the string is Jack is a boy, it matches the a after the J.

This regex can match the second a too. It only does so when you tell the regex engine to start searching through the string after the first match. In a text editor, you can do so by using its “Find Next” or “Search Forward” function. In a programming language, there is usually a separate function that you can call to continue searching through the string after the previous match.

Twelve characters have special meanings in regular expressions: the backslash , the caret ^, the dollar sign $, the period or dot ., 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 {. These special characters are often called “metacharacters”. Most of them are errors when used alone.

If you want to use any of these characters as a literal in a regex, you need to escape them with a backslash. If you want to match 1+1=2, the correct regex is 1+1=2. Otherwise, the plus sign has a special meaning.

Non-Printable Characters

You can use special character sequences to put non-printable characters in your regular expression. Use t to match a tab character (ASCII 0x09), r for carriage return (0x0D) and n for line feed (0x0A). More exotic non-printables are a (bell, 0x07), e (escape, 0x1B), f (form feed, 0x0C) and v (vertical tab, 0x0B). Remember that Windows text files use rn to terminate lines, while UNIX text files use n.

If your application supports Unicode, use uFFFF or x{FFFF} to insert a Unicode character. u20AC or x{20AC} matches the euro currency sign.

If your application does not support Unicode, use xFF to match a specific character by its hexadecimal index in the character set. xA9 matches the copyright symbol in the Latin-1 character set.

All non-printable characters can be used directly in the regular expression, or as part of a character class.

Character Classes or Character Sets

A “character class” matches only one out of several characters. To match an a or an e, use [ae]. You could use this in gr[ae]y to match either gray or grey. A character class matches only a single character. gr[ae]y does not match graay, graey or any such thing. The order of the characters inside a character class does not matter.

You can use a hyphen inside a character class to specify a range of characters. [0-9] matches a single digit between 0 and 9. You can use more than one range. [0-9a-fA-F] matches a single hexadecimal digit, case insensitively. You can combine ranges and single characters. [0-9a-fxA-FX] matches a hexadecimal digit or the letter X.

Typing a caret after the opening square bracket negates the character class. The result is that the character class matches any character that is not in the character class. q[^x] matches qu in question. It does not match Iraq since there is no character after the q for the negated character class to match.

Shorthand Character Classes

d matches a single character that is a digit, w matches a “word character” (alphanumeric characters plus underscore), and s matches a whitespace character (includes tabs and line breaks). The actual characters matched by the shorthands depends on the software you’re using. In modern applications, they include non-English letters and numbers.

The Dot Matches (Almost) Any Character

The dot matches a single character, except line break characters. Most applications have a “dot matches all” or “single line” mode that makes the dot match any single character, including line breaks.

gr.y matches gray, grey, gr%y, etc. Use the dot sparingly. Often, a character class or negated character class is faster and more precise.

Anchors

Anchors do not match any characters. They match a position. ^ matches at the start of the string, and $ matches at the end of the string. Most regex engines have a “multi-line” mode that makes ^ match after any line break, and $ before any line break. E.g. ^

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