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https://github.com/stdlib-js/string-pad

Pad a string.
https://github.com/stdlib-js/string-pad

align center javascript justify left lpad node node-js nodejs pad padding padstr right stdlib str string util utilities utility utils

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Pad a string.

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README 

        



  

    About stdlib...

  

  
We believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js.


  
The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases.


  
When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.


  
To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!



# pad



[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] 



> Pad a string.



## Installation



```bash

npm install @stdlib/string-pad

```



Alternatively,



-   To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]).

-   If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions).

-   For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]).

-   To use as a general utility for the command line, install the corresponding [CLI package][cli-section] globally.



The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships.



To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.



## Usage



```javascript

var pad = require( '@stdlib/string-pad' );

```



#### pad( str, len\[, options] )



Pads a `string` such that the padded `string` has a `length` of `len`.



```javascript

var str = pad( 'a', 5 );

// returns 'a    '

```



The function accepts the following `options`:



-   **lpad**: `string` used to left pad. Default: `''`.

-   **rpad**: `string` used to right pad. Default: `' '`.

-   **centerRight**: `boolean` indicating whether to center right in the event of a tie. Default: `false` (i.e., center left).



By default, an input `string` is padded with spaces. To pad with a different character or sequence of characters, provide a pad `string`.



```javascript

var str = pad( 'a', 10, {

    'lpad': 'b'

});

// returns 'bbbbbbbbba'



str = pad( 'a', 12, {

    'rpad': 'b'

});

// returns 'abbbbbbbbbbb'

```



To center an input `string`, provide both `lpad` and `rpad` options.



```javascript

var opts = {

    'lpad': 'a',

    'rpad': 'c'

};



var str = pad( 'b', 11, opts );

// returns 'aaaaabccccc'

```



When both `lpad` and `rpad` are specified and `len-str.length` is **odd**, left and right padding cannot equally split the available padding space. By default, right padding receives the extra character (i.e., the input `string` is left-centered).



```javascript

var opts = {

    'lpad': 'a',

    'rpad': 'c'

};



var str = pad( 'b', 10, opts );

// returns 'aaaabccccc'

```



To center right, set the `centerRight` option.



```javascript

var opts = {

    'lpad': 'a',

    'rpad': 'c',

    'centerRight': true

};



var str = pad( 'b', 10, opts );

// returns 'aaaaabcccc'

```



## Notes



-   In contrast to [lpad][@stdlib/string/left-pad] and [rpad][@stdlib/string/right-pad], any padding which does not evenly divide available space is trimmed such that the returned `string` length is **always** `len`.



    ```javascript

    var opts = {

        'lpad': 'boop',

        'rpad': 'woot'

    };

    var str = pad( 'beep', 10, opts );

    // returns 'boobeepwoo'

    ```



-   Similarly, if `len < str.length`, the input `string` is trimmed.



    ```javascript

    // Pad right, trim right:

    var str = pad( 'beep', 2 );

    // returns 'be'



    // Pad left, trim left:

    str = pad( 'beep', 2, {

        'lpad': 'b'

    });

    // returns 'ep'



    // Pad both, trim both:

    str = pad( 'beep', 2, {

        'lpad': '@',

        'rpad': '!'

    });

    // returns 'ee'



    // Pad both, trim both starting from left:

    str = pad( 'abcdef', 3, {

        'lpad': '@',

        'rpad': '!'

    });

    // returns 'cde'



    // Pad both, trim both starting from right:

    str = pad( 'abcdef', 3, {

        'lpad': '@',

        'rpad': '!',

        'centerRight': true

    });

    // returns 'bcd'

    ```



## Examples



```javascript

var round = require( '@stdlib/math-base-special-round' );

var randu = require( '@stdlib/random-base-randu' );

var pad = require( '@stdlib/string-pad' );



var str = 'boop';

var out;

var len;

var i;



for ( i = 0; i < 100; i++ ) {

    len = round( randu()*10.0 ) + str.length;

    out = pad( str, len, {

        'lpad': 'beep',

        'rpad': 'p'

    });

    console.log( '%s. %d. %d.', out, len, out.length );

}

```



* * *



## CLI



## Installation



To use as a general utility, install the CLI package globally



```bash

npm install -g @stdlib/string-pad-cli

```



### Usage



```text

Usage: padstr [options] [] --len 



Options:



  -h,    --help                Print this message.

  -V,    --version             Print the package version.

         --len length          String length.

         --lpad str            String used to left pad. Default: ''.

         --rpad str            String used to right pad. Default: ' '.

         --cright              Center right in the event of a tie.

         --split sep           Delimiter for stdin data. Default: '/\\r?\\n/'.

```



### Notes



-   If the split separator is a [regular expression][mdn-regexp], ensure that the `split` option is either properly escaped or enclosed in quotes.



    ```bash

    # Not escaped...

    $ echo -n $'beep\nboop' | padstr --len 10 --split /\r?\n/



    # Escaped...

    $ echo -n $'beep\nboop' | padstr --len 10 --split /\\r?\\n/

    ```



-   The implementation ignores trailing delimiters.



### Examples



```bash

$ padstr beep --len 10 --lpad b --rpad p

bbbbeepppp

```



To use as a [standard stream][standard-streams],



```bash

$ echo -n 'beep' | pad --len 9 --lpad a --rpad o

aabeepooo

```



By default, when used as a [standard stream][standard-streams], the implementation assumes newline-delimited data. To specify an alternative delimiter, set the `split` option.



```bash

$ echo -n 'beep\tboop' | pad --len 9 --lpad a --rpad o --split '\t'

aabeepooo

aaboopooo

```



* * *



## See Also



-   [`@stdlib/string-left-pad`][@stdlib/string/left-pad]: left pad a string.

-   [`@stdlib/string-right-pad`][@stdlib/string/right-pad]: right pad a string.



* * *



## Notice



This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.



For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].



#### Community



[![Chat][chat-image]][chat-url]



---



## License



See [LICENSE][stdlib-license].



## Copyright



Copyright © 2016-2024. The Stdlib [Authors][stdlib-authors].



[npm-image]: http://img.shields.io/npm/v/@stdlib/string-pad.svg

[npm-url]: https://npmjs.org/package/@stdlib/string-pad



[test-image]: https://github.com/stdlib-js/string-pad/actions/workflows/test.yml/badge.svg?branch=main

[test-url]: https://github.com/stdlib-js/string-pad/actions/workflows/test.yml?query=branch:main



[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/string-pad/main.svg

[coverage-url]: https://codecov.io/github/stdlib-js/string-pad?branch=main



[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg

[chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im



[stdlib]: https://github.com/stdlib-js/stdlib



[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors



[cli-section]: https://github.com/stdlib-js/string-pad#cli

[cli-url]: https://github.com/stdlib-js/string-pad/tree/cli

[@stdlib/string-pad]: https://github.com/stdlib-js/string-pad/tree/main



[umd]: https://github.com/umdjs/umd

[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules



[deno-url]: https://github.com/stdlib-js/string-pad/tree/deno

[deno-readme]: https://github.com/stdlib-js/string-pad/blob/deno/README.md

[umd-url]: https://github.com/stdlib-js/string-pad/tree/umd

[umd-readme]: https://github.com/stdlib-js/string-pad/blob/umd/README.md

[esm-url]: https://github.com/stdlib-js/string-pad/tree/esm

[esm-readme]: https://github.com/stdlib-js/string-pad/blob/esm/README.md

[branches-url]: https://github.com/stdlib-js/string-pad/blob/main/branches.md



[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/string-pad/main/LICENSE



[standard-streams]: https://en.wikipedia.org/wiki/Standard_streams



[mdn-regexp]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions



[@stdlib/string/left-pad]: https://github.com/stdlib-js/string-left-pad



[@stdlib/string/right-pad]: https://github.com/stdlib-js/string-right-pad