---
title: "Expressions régulières - Bases et utilisations fréquentes"
slug: "regular-expressions-basics-and-common-syntaxes"
updated: 2022-11-12T22:26:37Z
published: 2022-11-12T22:26:37Z
canonical: "help.cooperlink.io/regular-expressions-basics-and-common-syntaxes"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://help.cooperlink.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Regular Expressions - Basics and Common Syntaxes

## Purpose of the article

This article specifies how to create a regular expression and it provides the most frequent syntaxes.

## References and test

The website [https://regex101.com](https://regex101.com) provides many resources and a powerful tool to analyze your regular expressions online.

## Regular expression basics

A regular expression consists of symbols that specify the rules that apply to the extraction of information in a string.

### Characters

The following symbols represent a character:

- [a-c]: an alphabetic character between a and c, lowercase / [A-C]: an alphabetic character between A and C, uppercase
- [a-zA-Z]: an alphabetic character between a and z, lowercase or uppercase
- [0-5]: a number between 0 and 5
- [^a-z]: the hat ^ is an inversion operator. This means that the character is anything but between a and z, lowercase
- [-_]: either a dash or underscore character (underscore)
- The dot represents any character

### Rehearsals

The following symbols specify the rules for repeating characters:

- a*: the asterisk allows an unlimited number of repetitions of character a
- a+: checks for the presence of one or more a characters
- s? : checks for zero or one character a
- (...)? : checks for the presence of no or one capture group
- a{3} or a{3,3}: exactly three repetitions of character a
- [a-zA-Z]{3,1}: three or more repetitions of characters between a and z, lowercase or uppercase.
- [0-1]{3,6}: between three and six repetitions of a digit between 0 and 1

### Conditions

- ^ : placed at the beginning of the expression, it indicates the beginning of the string. This means that it forces the expression to evaluate successfully from the first character.
- $ : placed at the end of the expression, it indicates the end of the string. This means that it forces the expression to evaluate successfully down to the last character.
- (...) : parentheses are used to create an expression capture group
- (?:...) : captures everything that is part of the group
- (?<name>...) : Named expression capture group. In Cooperlink, the use of a field's key allows it to be identified with the field concerned. If the group refers to a field of type list of values, its capture must be one of the values encoded in Cooperlink to be successfully extracted.

## Example

### Filename with structure [code]-[title]-[revision]

Let's decode the following regular expression with the structure [CODE]-[TITLE]-[REVISION]:

```none
DEMO[-_](?<demo_en_document_status>[a-zA-Z]{2,2})[_-](?<demo_en_type>[a-zA-Z]{2,2})[_-](?<demo_en_package>[a-zA-Z]{4,4})[_-](?<demo_en_number>[0-9]{3,3})-(?<title>.*?)(?:[_-](?<demo_en_revision_number>[a-zA-Z]))?$
```

The character string is evaluated as follows:

- It must start with DEMO
- Then followed by a dash or underscore (underscore)
- The following characters must be alphabetic, 2 in number, lowercase or uppercase. These 2 letters will be captured in group **demo_en_document_status**. Within Cooperlink, in case of a list of values, the 2-character code extracted must be one of the values encoded in the configuration of the field.
- Then followed by a dash or underscore (underscore)
- The following characters must be alphabetic, 2 in number, lowercase or uppercase (group **demo_en_type**).
- Then followed by a dash or underscore (underscore)
- The following characters must be alphabetic, 4 in number, lowercase or uppercase (group **demo_en_package**).
- Then followed by a dash or underscore (underscore)
- The following characters must be numeric, 3 in number (group**demo_en_number**)
- Then followed by a dash
- An indeterminate string is then captured in a **title**group . The asterisk guarantees the positive evaluation of the expression until the last character following the presence of the $ character at the end of the string.
- A single alphabetic character, lowercase or uppercase, is optionally present at the end of the string, and preceded by a dash or underscore. This is captured as a revision index in group **demo_en_revision_number**.

### Excerpt from regex101

![](https://cdn.document360.io/c21b52e3-341e-4ea9-8692-3488bd21cd8d/Images/Documentation/image-1668290923363.png)