---
title: regexp.findString() function
description: >
  `regexp.findString()` returns the left-most regular expression match in a string.
menu:
  flux_v0_ref:
    name: regexp.findString
    parent: regexp
    identifier: regexp/findString
weight: 101
---

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



##### Function type signature

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

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

## Parameters

### r
({{< req >}})
Regular expression used to search `v`.



### v
({{< req >}})
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)}))

```

{{< expand-wrapper >}}
{{% expand "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   |

{{% /expand %}}
{{< /expand-wrapper >}}