How to use regular expressions
- Technical Communications
- Pooja Gopalnaidu
Overview
A number of apps provide advanced features that require the use of regular expressions for pattern matching. Generally, just a simple understanding of regular expressions and a few examples are enough to get by for most use cases. This page has a few simple examples to get started. Use the references for more advanced information. We recommend testing your regular expressions in one of the well-known regex testing sites such as RegexPlanet or Regex101.
Regex for workflow conditions
For Jira workflow functions using regex expressions to condition whether the post function should continue processing, a blank pattern means that condition processing is not done and processing should continue.
Dot or period (.) is a special regex character. If you really want to match on it, you need to escape it with a backslash: \.
Don't be confused with generic pattern matching used for file systems for instance. On a file system, *.png means all files ending with .png. That is an illegal regex expression. For regex you need: .*\.png. Or to simplify: .*png which will find all files ending in png (not necessarily ending in an extension of png).
Regex is case sensitive by default. In most cases, use the case insensitive flag: (?i). See one of the examples below.
Dotall mode when you need to match across line breaks.
In dotall mode, the expression . matches any character, including a line terminator. By default this expression does not match line terminators. Dotall mode can also be enabled via the embedded flag expression (?s). (The s is a mnemonic for "single-line" mode, which is what this is called in Perl.)
Simple examples
Value | Regex | Matches | Demonstrates |
|---|---|---|---|
ABC | A.C | . matches any single character | |
ABC | A.* |
| |
ABC | .*C |
| |
A.B | A\.B | Escape special regex characters with backslash if necessary | |
ABC | AB* | Regex is NOT generic matching | |
ABC | A.+ | + indicates 1 or more | |
ABC | ABC.+ |
| |
ABC | ABC.* |
| |
ABCD | ABC.* |
| |
ABC | [ABCD]* | [ ] indicates a class of characters | |
ABC | [ABZ] |
| |
ABC8 | [A-Z0-9] |
| |
ABC | [AB^C] | ^ in a class means NOT the following character | |
ABC | DEF|ABC | | indicates OR | |
image.png | .*png|.*jpg |
| |
image.jpg | .*png|.*jpg |
| |
image.JPG | .*png|.*jpg | defaults to case sensitive matching | |
image.JPG | (?i).*png|.*jpg | (?i) indicates case insensitive matching | |
ABAB | (AB)+ | () indicates a grouping | |
ABCD | (AB)+ |
| |
112233 | \d+ | \d for digits | |
A B | A\s*B | \s for whitespace | |
ABC | \S* | \S for non whitespace | |
| \S+ | Value must have at least 1 non whitespace character | |
A | \S+ |
| |
XYZ,ABC,UVW | .*\bABC\b.* | Word boundaries. Finding words in a comma or blank separated list using word boundaries | |
XYZ,ABCD,UVW | .*\bABC\b.* |
| |
ABC | (?m)(^ABC$)|(^ABC,)|(,ABC,)|(,ABC$) | Looking for text matches in a comma separated list by covering all cases: only, start, middle, and end. This uses the multi-line flag: (?m) | |
XYZ,ABC,UVW | (?m)(^ABC$)|(^ABC,)|(,ABC,)|(,ABC$) |
| |
XYZ,ABC DEF,UVW | (?m)(^ABC$)|(^ABC,)|(,ABC,)|(,ABC$) |
|
Advanced examples
Value | Regex | Matches | Find | Demonstrates |
|---|---|---|---|---|
example.txt |
| Find string not containing a word. In this example, files that do not have a .png extension | ||
example.png |
| Find string not containing a word. In this example, files that do not have a .png extension | ||
example.jpeg |
| Find string not containing a word. In this example, files that do not have a .png or .jpeg extension | ||
collateral wholesale retail |
|
| Match exact words anywhere in string. In this case a blank separated list of labels and we require both collateral and retail to be included before we want the match to be successful | |
wholesale retail |
|
| Both are required for a match | |
merger acquisition |
|
| Match string containing either word |
References
RegexOne - interactive tutorials to learn how to construct regular expressions
Regexlib.com - searchable collection of user-contributed regular expressions
RegexPlanet test site - test your expressions quickly
Regex101 test site - understand a regex expression and test it
Quick reference - best once you have the concepts
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