Works like OR. Expects one of the expressions it separates to match.

Alternation

Matches the preceding item zero or more times.

Asterisk

Matches the beginning of the string or line.

Start of string or line

Ignore Case

Character Set

Digit

End of string or line

Matches any character except line breaks.

Ensures that the expression does not stop on the first match.

Global

Group

Makes ^ and $ match at the start and end of each line. Without it, they only match at the start and end of the whole string.

Multiline

Negated Character Set

Negative Lookahead

Negative Lookbehind

Makes a grouping that cannot be referenced.

Non-capturing Group

Matches any character that is not a digit.

Not Digit

Not Whitespace

Matches any character that is not alphanumeric or an underscore.

Not Word

Matches a position that is not at the start or end of a word.

Not Word Boundary

Optional

Matches the preceding item one or more times.

Plus

Positive Lookahead

Positive Lookbehind

Matches the preceding item a specific number of times, or within a range.

Quantifier

Matches all characters between two characters, including themselves.

Range

Reference

Whitespace

Matches any alphanumeric character, including the underscore.

Word

Matches a position at the start or end of a word.

Word Boundary

Use the asterisk `*` to write the expression that will select each word where the letter `e` is absent or is present one or more times.

Practice: Asterisk `*`

Write the expression that selects every `of` in the text.

Practice: Basic Matcher

Write the expression that matches each word in the text. The only character that changes is the first letter of each word.

Practice: Character Sets

Type the expression to select individual letters, numbers, spaces, and special characters in the text. The expression you type must match any character.

Practice: Any Character

Practice completed!

Write the expression that matches every word in the text except `beor` and `beur`. Use a negated character set to do this.

Practice: Negated Character Sets

Write the expression using the plus sign `+` to select words in which the letter `e` occurs one or more times in the text.

Practice: Plus Sign `+`

Write the expression that finds numbers made of `4` digits in a row, using curly braces `{}`. Remember that the range `[0-9]` matches a single digit.

Practice: Curly Braces - 1

Write the expression that finds numbers with at least `2` digits in a row, using curly braces `{}`.

Practice: Curly Braces - 2

Write the expression that finds numbers with at least `1` and at most `4` digits in a row, using curly braces `{}`.

Practice: Curly Braces - 3

Write the expression indicating that the letter `n` is optional in the text, using the question mark `?`. Thus, both the words `a` and `an` can be selected.

Practice: Question Mark `?`

Write the expression that selects the letters from `g` to `k` in the text.\n`g` and `k` should also be included in the range.

Practice: Letter Range

Write the expression that selects the digits from `2` to `7` in the text.\n`2` and `7` should also be included in the range.

Practice: Number Range

Now it's time to do some practice to consolidate what we've learned.

Practice

Learning Regex is easier than you think. You can use this tool to easily `learn`, `practice` and `test` Regex.

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Learn Regex step by step, from zero to advanced.

In regex, the period `.` matches any single character, including spaces. The asterisk `*` means the preceding item can occur zero or more times. Used together, `.*` matches any sequence of characters of any length.\n\nBelow are various keywords. Add `.*` to the end of the regex to write the expression that starts with `how to write` and matches everything after it.

Anything `.*`

Let's take a look at some regex patterns you will use often. To learn more about them, we recommend the `Regex 101` tutorial. Type `Yes` to get started.

Basics

Let's say we have a list of URLs, and we want to find only those URLs that start with `http`. But URLs also contain `http` in different parts other than their beginning. Add a caret `^` to the beginning of the following expression to filter only those starting with `http`.

Caret Sign `^`

To filter text that contains a word or phrase, we write it between two `.*` patterns, which match everything. For example, type `.*buy.*` to filter for text that includes `buy`.

Contains

Again we have a list of URLs. We want to find only those URLs ending in `.htm`.\n\nSince the period `.` is a special character that matches everything, we first need to escape the period before `htm` with the escape character `\`. This applies to all special characters.\n\nThen add a `$` sign to the end of the expression. This ensures that the text to be filtered ends with the expression written before it.

Dollar Sign `$` and Escape Character `\`

Here is an example of using regex in the `.htaccess` file. In the example, links with the `php` extension are redirected to their `html` versions with a `301` redirect.

.htaccess

We may want to filter results by their length. For example, to filter URLs that are exactly `35` characters long, add the length in curly braces `{35}` right after the period `.`.

Length Restrictions `{n}`

To filter URLs that are at most `35` characters long, add the minimum and maximum length in curly braces `{1,35}` right after the period `.`.

Length Restrictions (Maximum) `{n,m}`

To filter URLs that are at least `35` characters long, add the minimum length followed by a comma in curly braces `{35,}` right after the period `.`.

Length Restrictions (Minimum) `{n,}`

We use negated character sets `[^abc]` to specify characters that must not appear. The characters are written inside square brackets, starting with a caret `^`. Below are both `http` and `https`. Since `http` appears in both, it also matches `https`. Type `[^s]` after the letter `p` to exclude the letter `s`.

Negated Character Sets `[^abc]`

We use it to express that a character or expression is optional. For example, we want to filter text containing either `http` or `https`. We could use the Or operator `|` for this, but there is a better way for these two almost identical words.\n\nIn this example, the letter `s` is optional. Add a question mark `?` after the letter `s`.

Optional Operator `?`

We use the Or operator `|` to filter for multiple expressions. For example, to filter text containing `seo` or `regex`, write both words separated by the Or operator `|`.

Or Operator `|`

Regex knowledge is a skill that increases productivity on any platform that allows you to use regex. Once you start using it and improve this skill, it will help you complete many repetitive tasks faster and save time for other things. To better understand the basics of Regex, you can visit the `Regex 101` tutorial. You can use the `Playground` page to test your own expressions on your own text.

Outro

Here is an example of regex-like usage in the `robots.txt` file. The example states that bots should not crawl links with the extension `pdf`.

robots.txt (regex-like syntax)

Regex (regular expressions) is a pattern language frequently used in many fields, especially by people who want to work more efficiently. Using Regex for SEO makes it easier to analyze large amounts of data and write richer filters. We recommend starting with the `Regex 101` tutorial if you are new to Regex.\n\nStart by typing `OK` in the Regex field to proceed to the first step and access more detailed explanations.

Regex for SEO

You can use Regex for SEO on platforms such as `Google Analytics`, `Google Data Studio`, `Google Sheets`, `Google Search Console`, `Ahrefs`, `Deepcrawl`, `Screaming Frog`. It is also frequently used in `.htaccess` and `robots.txt (regex-like syntax)` files.\n\nBelow is a sample regex that will select only texts in the list that start with `Google`.

Use Cases

You can learn the basics of Regex in this tutorial.

Regex 101 - EN

In this tutorial, you can learn how and where you can use Regex for SEO.

Regex for SEO - EN

Regex Learn - Not Found

Sometimes you just need to remember Regex. Try the cheatsheet that will make it easier for you to understand and remember better.

Regex Learn - Regex Cheatsheet

Learn Regex interactively, practice at your level, and test your own Regex.

Regex Learn - Step by step, from zero to advanced.

Learn Regex step by step. Complete the interactive tutorial that will make your learning easier and faster.

Regex Learn - Regex Interactive Course

You can easily build and test your regex pattern online via Playground.

Regex Learn - Playground

With `RegexLearn Cheatsheet`, you can see all of the usages you need at once and check them on a single page. Explore all Regex patterns and symbols with the Regex cheat sheet.

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Cheatsheet

`Regular Expressions`, abbreviated as Regex or Regexp, are sequences of characters that describe a pattern using regex syntax rules. You can easily manage your data with Regex, which uses commands like finding, matching, and editing. You can use Regex in programming languages such as Python, SQL, JavaScript and R, in tools like Google Analytics and Google Data Studio, and throughout the coding process. Learn regex online with examples and tutorials on `RegexLearn` now.

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Learn

Regex Learn is an open-source project that welcomes community contributions and is free to use. Working on this project allows you to hone your skills, study, and collaborate. You can contribute & support here.

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Open Source

If you want to generate a Regex, you can easily build, validate and test your Regex pattern in the Playground.

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Playground

Once you've completed the learning section, it's time to practice! The practice section will help you reinforce your Regex knowledge with exercises for every level. Coming soon.

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We put an asterisk `*` after a character to indicate that the character may either not match at all or can match many times. For example, indicate that the letter `e` may not occur in the text at all, or may occur once or more side by side.

Asterisk `*`

The character or word we want to find is written directly, just like a normal search. For example, to find the word `curious` in the text, type it as it is.

Basic Matchers

We were using `[0-9]` to find digits. To find only the digits at the beginning of a line, put the `^` sign at the start of this expression.

Caret Sign `^`:\nSelecting by Line Start

If a character in a word can be one of several characters, we write all the alternatives inside square brackets `[]`. For example, to write an expression that finds all the words in the text, type the characters `a`, `e`, `i`, `o`, `u` next to each other inside the square brackets `[]`.

Character Sets `[abc]`

You can return to the previous steps whenever you want, and you can easily navigate through all the steps you have passed.

Congratulations, you have completed all the steps!

Add the `$` sign after `html` to find `html` only at the end of a line.

Dollar Sign `$`:\nSelecting by End of Line

The period `.` allows selecting any character, including special characters and spaces. Type a period `.` in the Regex field to proceed.

Dot `.`: Any Character

Some characters have a special meaning in regex: `{ } [ ] ( ) / \ + * . $ ^ | ?` To match these characters themselves, we need to put an escape character `\` before them. For example, to select the dot `.` and asterisk `*` characters in the text, add an escape character `\` before each of them.

Escape Character `\`

Flags change how an expression matches, which is why they are also called `modifiers`. They determine whether the expression treats the text as separate lines, whether it is case-sensitive, and whether it finds all matches. Continue to the next step to learn about flags.

Flags

To make the expression ignore the difference between uppercase and lowercase letters, enable the `case-insensitive` flag.

Case-insensitive Flag

The `global` flag makes the expression select all matches. If it is not used, only the first match is selected. Now enable the `global` flag to select all matches.

Global Flag

By default, regex treats the whole text as a single line. The `multiline` flag makes it handle each line separately, so expressions that use the start `^` or end `$` of a line work for every line. Now enable the `multiline` flag to find all matches.

Multiline Flag

Regex does greedy matching by default, which means a match is as long as possible. Look at the example below: it matches anything that ends with `r` and is preceded by any characters, but it does not stop at the first `r`.

Greedy Matching

Below, we have two groups: `(ha)` and `(haa)`. When we want to reference these groups later in the pattern, we use `\1` for the first group and `\2` for the second group. For example, in the pattern `(ha)-\1,(haa)-\2`, the `-` is outside the groups, and `\1` refers to `ha` while `\2` refers to `haa`. Type `\2` at the end of the expression to refer to the second group.

Referencing a Group

We can group an expression and then reference the group or apply rules to it. To group an expression, we put it in parentheses `()`. For now, just group `haa` below.

Parentheses `( )`: Grouping

Lazy matching, unlike greedy matching, stops at the first possible match. In the example below, add a `?` after `*` to find the first match that ends with the letter `r` and is preceded by any characters. This makes the match stop at the first `r`.

Lazy Matching

If we want an expression to match only when it comes before or after another expression, we use lookarounds. Continue to the next step to learn how they work.

Lookarounds

To find all words in the text below, except for `ber` and `bor`, type `e` and `o` side by side after the caret `^` character inside square brackets `[]`.

For example, we want to select the numbers in the text other than the hour value. To select only the numbers not followed by `PM`, we write the negative lookahead `(?!)` after our expression. Add `PM` after the `!` sign inside the parentheses.

Negative Lookahead: `(?!)`

For example, we want to select the numbers in the text other than the price value. To select only the numbers not preceded by `$`, we write the negative lookbehind `(?<!)` before our expression. Add `\$` after the `!` sign inside the parentheses.

Negative Lookbehind: `(?<!)`

Adding `?:` right after the opening parenthesis, like `(?:ha)`, makes a group non-capturing: it still groups the expression, but its match is not stored, so it cannot be referenced. Below, the first group `(?:ha)` is non-capturing. That is why the reference `\1` refers to the capturing group `(haa)`. Type `\1` at the end of the expression to reference the grouped `haa`.

Parentheses `(?: )`: Non-capturing Grouping

Digit Character `\d`

It lets you specify that an expression can be one of several different expressions. All possible expressions are written separated by the pipe sign `|`. This differs from a character set `[abc]`: character sets operate at the character level. Alternatives are at the expression level. For example, the following expression would select both `cat` and `rat`. Add another pipe sign `|` to the end of the expression and type `dog` so that all words are selected.

Pipe Character `|`

To indicate that a character must occur one or more times, we put a plus sign `+` after a character. For example, indicate that the letter `e` must occur one or more times in the text.

Plus Sign `+`

For example, we want to select the hour value in the text. To select only the numbers followed by `PM`, we write the positive lookahead `(?=)` after our expression. Add `PM` after the `=` sign inside the parentheses.

Positive Lookahead: `(?=)`

For example, we want to select the price value in the text. To select only the numbers preceded by `$`, we write the positive lookbehind `(?<=)` before our expression. Add `\$` after the `=` sign inside the parentheses.

Positive Lookbehind: `(?<=)`

To require a character to occur a specific number of times, we write that number in curly braces `{n}` right after it. For example, indicate that the following letter `e` must occur exactly `2` times in a row.

Curly Braces - 1

To require a character to occur at least a certain number of times, we write that number followed by a comma inside curly braces `{n,}` right after it. For example, indicate that the following letter `e` must occur at least `3` times in a row.

Curly Braces - 2

To require a character to occur within a range of times, we write the minimum and maximum inside curly braces `{x,y}` right after it; both limits are inclusive. For example, indicate that the following letter `e` must occur between `1` and `3` times in a row.

Curly Braces - 3

To indicate that a character is optional, we put a `?` question mark after a character. For example, indicate that the following letter `u` is optional.

Question Mark `?`

To find letters in a range, we write the first and last letters inside square brackets `[]` with a dash `-` between them. It is case-sensitive. Type the expression that selects all lowercase letters from `e` to `o`, including `e` and `o`.

Letter Range `[a-z]`

To find digits in a range, we write the first and last digits inside square brackets `[]` with a dash `-` between them. Type the expression that selects all digits from `3` to `6`, including `3` and `6`.

Number Range `[0-9]`

Some special characters are used to specify how many times a character can repeat, or whether it appears at all. These special characters are the plus `+`, the asterisk `*` and the question mark `?`.

Repetitions

`\s` is used to find only whitespace characters, such as spaces, tabs and line breaks.

Whitespace Character `\s`

Regex is short for `Regular Expression`. It helps to match, find or manage text. The lessons and the Playground use JavaScript's regex engine, where a pattern is written as `/pattern/flags`. Start by typing `OK` in the Regex field to proceed to the first step and access the more detailed description.

Intro

Regular Expressions are a string of characters that express a search pattern. They are often abbreviated as `Regex` or `Regexp`. They are especially used to find or replace words in texts. In addition, we can test whether a text complies with the rules we set.\n\n For example, let's say you have a list of filenames. And you only want to find files with the `pdf` extension. Then typing an expression like `^\w+\.pdf$` will do the job. The meaning of the definitions in this expression will become clearer as the steps progress.

What are Regular Expressions `Regex`?

`\D` is used to find any character that is not a digit.

Non-digit Characters `\D`

`\S` is used to find any character that is not whitespace.

Non-whitespace Characters `\S`

The expression `\W` is used to find characters other than letters, numbers, and underscores.

Non-word Characters `\W`

The expression `\w` is used to find letters, numbers and underscore characters. Let's use the expression `\w` to find word characters in the text.

Cheatsheet

Anchors

Flags

Groups & References

Character Classes

Lookarounds

Quantifiers and Alternation