---
title: Work with regular expression types
description: A regular expression type represents a regular expression pattern. Learn how to work with Flux regular expression types.
url: https://docs.influxdata.com/flux/v0/data-types/basic/regexp/
estimated_tokens: 2418
product: Flux
version: v0
---

# Work with regular expression types

A **regular expression** type represents a regular expression pattern.

**Type name**: `regexp`

-   [Regular expression syntax](#regular-expression-syntax)
-   [Use regular expression flags](#use-regular-expression-flags)
-   [Use regular expressions in predicate expressions](#use-regular-expressions-in-predicate-expressions)
-   [Convert a string to a regular expression](#convert-a-string-to-a-regular-expression)
-   [Examples](#examples)

## Regular expression syntax

Flux uses the [Go regexp implementation and syntax](https://pkg.go.dev/regexp). This syntax is similar to regular expressions in Perl, Python, and other languages. Regular expression literals are enclosed in forward slash characters (`/`).

```js
/^[a-z0-9]+$/
```

## Use regular expression flags

Flux supports the following regular expression flags:

| Flag | Description |
| --- | --- |
| i | case-insensitive |
| m | multi-line mode: ^ and $ match begin/end line in addition to begin/end text |
| s | let . match \n |
| U | ungreedy: swap meaning of x* and x*?, x+ and x+?, etc |

Include regular expression flags at the beginning of your regular expression pattern enclosed in parentheses (`()`) and preceded by a question mark (`?`).

```js
/(?iU)foo*/
```

## Use regular expressions in predicate expressions

To use regular expressions in [predicate expressions](/flux/v0/get-started/syntax-basics/#predicate-expressions), use the [`=~` and `!~` comparison operators](/flux/v0/spec/operators/#comparison-operators). The left operand must be a string. The right operand must be a regular expression.

```js
"abc" =~ /\w/
// Returns true

"z09se89" =~ /^[a-z0-9]{7}$/
// Returns true

"foo" !~ /^f/
// Returns false

"FOO" =~ /(?i)foo/
// Returns true

```

## Convert a string to a regular expression

1. Import the [`regexp` package](/flux/v0/stdlib/regexp/).
2. Use [`regexp.compile()`](/flux/v0/stdlib/regexp/compile) to compile a string into a regular expression type.

```js
import "regexp"

regexp.compile(v: "^- [a-z0-9]{7}")
// Returns ^- [a-z0-9]{7} (regexp type)

```

## Examples

-   [Replace all substrings that match a regular expression](#replace-all-substrings-that-match-a-regular-expression)
-   [Return the first regular expression match in a string](#return-the-first-regular-expression-match-in-a-string)
-   [Escape regular expression metacharacters in a string](#escape-regular-expression-metacharacters-in-a-string)

### Replace all substrings that match a regular expression

1. Import the [`regexp` package](/flux/v0/stdlib/regexp).
    
2. Use [`regexp.replaceAllString()`](/flux/v0/stdlib/regexp/replaceallstring/) and provide the following parameters:
    
    -   **r**: regular expression
    -   **v**: string to search
    -   **t**: replacement for matches to **r**.

```js
import "regexp"

regexp.replaceAllString(r: /a(x*)b/, v: "-ab-axxb-", t: "T")
// Returns "-T-T-"

```

### Return the first regular expression match in a string

1. Import the [`regexp` package](/flux/v0/stdlib/regexp).
    
2. Use [`regexp.findString()`](/flux/v0/stdlib/regexp/findstring/) to return the first regular expression match in a string. Provide the following parameters:
    
    -   **r**: regular expression
    -   **v**: string to search

```js
import "regexp"

regexp.findString(r: /foo.?/, v: "seafood fool")
// Returns "food"

```

### Escape regular expression metacharacters in a string

If a string contains regular expression metacharacters that should be evaluated as literal characters, escape the metacharacters before converting the string to a regular expression:

1. Import the [`regexp` package](/flux/v0/stdlib/regexp).
2. Use [`regexp.quoteMeta()`](/flux/v0/stdlib/regexp/quotemeta/) and provide the string to escape regular expression metacharacters in:

```js
import "regexp"

regexp.quoteMeta(v: ".+*?()|[]{}^$")
// Returns "\.\+\*\?\(\)\|\[\]\{\}\^\$"

```

#### Related

-   [regexp package](/flux/v0/stdlib/regexp/)

[regexp types](/flux/v0/tags/regexp-types/) [data types](/flux/v0/tags/data-types/)