---
title: regexp.findString() function
description: regexp.findString() returns the left-most regular expression match in a string.
url: https://docs.influxdata.com/flux/v0/stdlib/regexp/findstring/
estimated_tokens: 1663
product: Flux
version: v0
---

# regexp.findString() function

-   Flux 0.33.0+
-   View InfluxDB support

`regexp.findString()` returns the left-most regular expression match in a string.

##### Function type signature

```js
(r: regexp, v: string) => string
```

For more information, see [Function type signatures](/flux/v0/function-type-signatures/).

## Parameters

### r

(Required) Regular expression used to search `v`.

### v

(Required) String value to search.

## Examples

-   [Return the first regular expression match in a string](#return-the-first-regular-expression-match-in-a-string)
-   [Find the first regular expression match in each row](#find-the-first-regular-expression-match-in-each-row)

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

```js
import "regexp"

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

```

### Find the first regular expression match in each row

```js
import "regexp"
import "sampledata"

regex = /.{6}$/

sampledata.string()
    |> map(fn: (r) => ({r with _value: regexp.findString(v: r._value, r: regex)}))
```

[](#view-example-input-and-output)

View example input and output

#### Input data

| _time | *tag | _value |
| --- | --- | --- |
| 2021-01-01T00:00:00Z | t1 | smpl_g9qczs |
| 2021-01-01T00:00:10Z | t1 | smpl_0mgv9n |
| 2021-01-01T00:00:20Z | t1 | smpl_phw664 |
| 2021-01-01T00:00:30Z | t1 | smpl_guvzy4 |
| 2021-01-01T00:00:40Z | t1 | smpl_5v3cce |
| 2021-01-01T00:00:50Z | t1 | smpl_s9fmgy |

| _time | *tag | _value |
| --- | --- | --- |
| 2021-01-01T00:00:00Z | t2 | smpl_b5eida |
| 2021-01-01T00:00:10Z | t2 | smpl_eu4oxp |
| 2021-01-01T00:00:20Z | t2 | smpl_5g7tz4 |
| 2021-01-01T00:00:30Z | t2 | smpl_sox1ut |
| 2021-01-01T00:00:40Z | t2 | smpl_wfm757 |
| 2021-01-01T00:00:50Z | t2 | smpl_dtn2bv |

#### Output data

| _time | _value | *tag |
| --- | --- | --- |
| 2021-01-01T00:00:00Z | g9qczs | t1 |
| 2021-01-01T00:00:10Z | 0mgv9n | t1 |
| 2021-01-01T00:00:20Z | phw664 | t1 |
| 2021-01-01T00:00:30Z | guvzy4 | t1 |
| 2021-01-01T00:00:40Z | 5v3cce | t1 |
| 2021-01-01T00:00:50Z | s9fmgy | t1 |

| _time | _value | *tag |
| --- | --- | --- |
| 2021-01-01T00:00:00Z | b5eida | t2 |
| 2021-01-01T00:00:10Z | eu4oxp | t2 |
| 2021-01-01T00:00:20Z | 5g7tz4 | t2 |
| 2021-01-01T00:00:30Z | sox1ut | t2 |
| 2021-01-01T00:00:40Z | wfm757 | t2 |
| 2021-01-01T00:00:50Z | dtn2bv | t2 |

#### Related

-   [regexp.splitRegexp() function](/flux/v0/stdlib/regexp/splitregexp/)
-   [Work with regular expression types](/flux/v0/data-types/basic/regexp/)