---
title: strings.hasPrefix() function
description: strings.hasPrefix() indicates if a string begins with a specified prefix.
url: https://docs.influxdata.com/flux/v0/stdlib/strings/hasprefix/
estimated_tokens: 1129
product: Flux
version: v0
---

# strings.hasPrefix() function

-   Flux 0.18.0+
-   View InfluxDB support

`strings.hasPrefix()` indicates if a string begins with a specified prefix.

##### Function type signature

```js
(prefix: string, v: string) => bool
```

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

## Parameters

### v

(Required) String value to search.

### prefix

(Required) Prefix to search for.

## Examples

### Filter based on the presence of a prefix in a column value

```js
import "sampledata"
import "strings"

sampledata.string()
    |> filter(fn: (r) => strings.hasPrefix(v: r._value, prefix: "smpl_5"))
```

[](#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 | *tag | _value |
| --- | --- | --- |
| 2021-01-01T00:00:40Z | t1 | smpl_5v3cce |

| _time | *tag | _value |
| --- | --- | --- |
| 2021-01-01T00:00:20Z | t2 | smpl_5g7tz4 |

#### Related

-   [strings.hasSuffix() function](/flux/v0/stdlib/strings/hassuffix/)