@stdlib/string/left-pad/README.md

String manipulation functions.

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# lpad

> Left pad a string.

<section class="usage">

## Usage

```javascript
var lpad = require( '@stdlib/string/left-pad' );
```

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

Left pads a string such that the padded string has a length of **at least** `len`.

```javascript
var str = lpad( 'a', 5 );
// returns '    a'
```

By default, an input string is padded with a Unicode "space" character (U+0020). To pad with a different character or sequence of characters, provide a `pad` string.

```javascript
var str = lpad( 'beep', 10, 'b' );
// returns 'bbbbbbbeep'

str = lpad( 'boop', 12, 'beep' );
// returns 'beepbeepboop'
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   An output string is **not** guaranteed to have a length of **exactly** `len`, but to have a length of **at least** `len`. To generate a padded string having a length equal to `len`

    ```javascript
    var str = lpad( 'boop', 10, 'beep' ); // => length 12
    // returns 'beepbeepboop'

    str = str.substring( str.length-10 ); // => length 10
    // returns 'epbeepboop'
    ```

-   This function differs from [`String.prototype.padStart`][mdn-string-padstart] in the following ways:

    -   The function is **not** guaranteed to return a string having a length exactly equal to `len` (as explained above).
    -   The function does **not** truncate `pad` (from the end) in order to ensure the returned string has length `len`.

    To replicate [`String.prototype.padStart`][mdn-string-padstart] truncation behavior

    ```javascript
    var floorb = require( '@stdlib/math/base/special/floorb' );

    function padStart( str, len, pad ) {
        var n;
        if ( len <= str.length ) {
            return str;
        }
        n = floorb( len-str.length, 1, pad.length ) + str.length;
        return pad.substring( 0, len-n ) + lpad( str, n, pad );
    }

    var str = padStart( 'boop', 10, 'beep' );
    // returns 'bebeepboop'
    ```

</section>

<!-- /.notes -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```javascript
var discreteUniform = require( '@stdlib/random/base/discrete-uniform' );
var lpad = require( '@stdlib/string/left-pad' );

var str = 'beep';
var i;
for ( i = 0; i < 100; i++ ) {
    console.log( lpad( str, discreteUniform( str.length, str.length+10 ), 'b' ) );
}
```

</section>

<!-- /.examples -->

* * *

<section class="cli">

## CLI

<section class="usage">

### Usage

```text
Usage: lpad [options] --len=<length> [<string>]

Options:

  -h,    --help                Print this message.
  -V,    --version             Print the package version.
         --len length          Minimum string length.
         --pad str             String used to pad. Default: ' '.
         --split sep           Delimiter for stdin data. Default: '/\\r?\\n/'.
```

</section>

<!-- /.usage -->

<!-- CLI usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

### 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' | lpad -len 8 --split /\r?\n/

    # Escaped...
    $ echo -n $'beep\nboop' | lpad -len 8 --split /\\r?\\n/
    ```

-   The implementation ignores trailing delimiters.

</section>

<!-- /.notes -->

<section class="examples">

### Examples

```bash
$ lpad beep --len 10 --pad b
bbbbbbbeep
```

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

```bash
$ echo -n 'beep' | lpad --len 8
    beep
```

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 'boop\tbeep' |  lpad --len 8 --split '\t'
    boop
    beep
```

</section>

<!-- /.examples -->

</section>

<!-- /.cli -->

<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/string/pad`][@stdlib/string/pad]</span><span class="delimiter">: </span><span class="description">pad a string.</span>
-   <span class="package-name">[`@stdlib/string/right-pad`][@stdlib/string/right-pad]</span><span class="delimiter">: </span><span class="description">right pad a string.</span>

</section>

<!-- /.related -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="links">

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

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

[mdn-string-padstart]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart

<!-- <related-links> -->

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

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

<!-- </related-links> -->

</section>

<!-- /.links -->