# isHexString
> Test whether a string contains only hexadecimal digits.
## Usage
```javascript
var isHexString = require( '@stdlib/assert/is-hex-string' );
```
#### isHexString( value )
Tests whether a string contains only hexadecimal digits.
```javascript
var bool = isHexString( '0123456789abcdefABCDEF' );
// returns true
```
## Notes
- For non-string values, the function returns `false`.
- The function does **not** recognize `x` (as in the standard `0x` prefix).
## Examples
```javascript
var isHexString = require( '@stdlib/assert/is-hex-string' );
var out = isHexString( '0123456789abcdefABCDEF' );
// returns true
out = isHexString( '' );
// returns false
out = isHexString( '0xffffff' );
// returns false
out = isHexString( 123 );
// returns false
```
* * *
## CLI
### Usage
```text
Usage: is-hex-string [options] []
Options:
-h, --help Print this message.
-V, --version Print the package version.
```
### Examples
```bash
$ is-hex-string 0123456789abcdefABCDEF
true
```
To use as a [standard stream][standard-streams],
```bash
$ echo -n '0123456789abcdefABCDEF' | is-hex-string
true
```
[standard-streams]: https://en.wikipedia.org/wiki/Standard_streams