---
title: strings.hasPrefix() function
description: >
  `strings.hasPrefix()` indicates if a string begins with a specified prefix.
menu:
  flux_v0_ref:
    name: strings.hasPrefix
    parent: strings
    identifier: strings/hasPrefix
weight: 101
---

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



##### Function type signature

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

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

## Parameters

### v
({{< req >}})
String value to search.



### prefix
({{< req >}})
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"))

```

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{{% 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                | *tag | _value      |
| -------------------- | ---- | ----------- |
| 2021-01-01T00:00:40Z | t1   | smpl_5v3cce |

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

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