213 lines
4.7 KiB
Markdown
213 lines
4.7 KiB
Markdown
<!--
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@license Apache-2.0
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Copyright (c) 2018 The Stdlib Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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# Left Pad
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> Left pad a string.
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<section class="usage">
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## Usage
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```javascript
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var lpad = require( '@stdlib/string/left-pad' );
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```
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#### lpad( str, len\[, pad] )
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Left pads a `string` such that the padded `string` has a `length` of **at least** `len`.
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```javascript
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var str = lpad( 'a', 5 );
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// returns ' a'
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```
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By default, an input `string` is padded with `spaces`. To pad with a different character or sequence of characters, provide a `pad` string.
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```javascript
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var str = lpad( 'beep', 10, 'b' );
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// returns 'bbbbbbbeep'
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str = lpad( 'boop', 12, 'beep' );
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// returns 'beepbeepboop'
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```
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</section>
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<!-- /.usage -->
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<section class="notes">
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## Notes
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- 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`
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```javascript
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var str = lpad( 'boop', 10, 'beep' ); // => length 12
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// returns 'beepbeepboop'
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str = str.substring( str.length-10 ); // => length 10
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// returns 'epbeepboop'
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```
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</section>
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<!-- /.notes -->
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<section class="examples">
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## Examples
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<!-- eslint no-undef: "error" -->
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```javascript
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var round = require( '@stdlib/math/base/special/round' );
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var randu = require( '@stdlib/random/base/randu' );
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var lpad = require( '@stdlib/string/left-pad' );
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var str = 'beep';
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var n;
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var i;
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for ( i = 0; i < 100; i++ ) {
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n = round( randu()*10 ) + str.length;
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console.log( lpad( str, n, 'b' ) );
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}
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```
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</section>
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<!-- /.examples -->
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* * *
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<section class="cli">
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## CLI
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<section class="usage">
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### Usage
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```text
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Usage: lpad [options] [<string>] --len=<length>
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Options:
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-h, --help Print this message.
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-V, --version Print the package version.
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--len length Minimum string length.
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--pad str String used to pad. Default: ' '.
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--split sep Delimiter for stdin data. Default: '/\\r?\\n/'.
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```
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</section>
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<!-- /.usage -->
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<!-- CLI usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="notes">
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### Notes
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- If the split separator is a [regular expression][mdn-regexp], ensure that the `split` option is either properly escaped or enclosed in quotes.
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```bash
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# Not escaped...
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$ echo -n $'beep\nboop' | lpad -len 8 --split /\r?\n/
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# Escaped...
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$ echo -n $'beep\nboop' | lpad -len 8 --split /\\r?\\n/
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```
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- The implementation ignores trailing delimiters.
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</section>
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<!-- /.notes -->
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<section class="examples">
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### Examples
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```bash
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$ lpad beep --len 10 --pad b
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bbbbbbbeep
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```
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To use as a [standard stream][standard-streams],
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```bash
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$ echo -n 'beep' | lpad --len 8
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beep
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```
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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.
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```bash
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$ echo -n 'boop\tbeep' | lpad --len 8 --split '\t'
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boop
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beep
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```
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</section>
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<!-- /.examples -->
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</section>
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<!-- /.cli -->
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<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
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<section class="related">
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* * *
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## See Also
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- <span class="package-name">[`@stdlib/string/pad`][@stdlib/string/pad]</span><span class="delimiter">: </span><span class="description">pad a string.</span>
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- <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>
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</section>
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<!-- /.related -->
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<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="links">
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[standard-streams]: https://en.wikipedia.org/wiki/Standard_streams
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[mdn-regexp]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions
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<!-- <related-links> -->
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[@stdlib/string/pad]: https://github.com/stdlib-js/string/tree/main/pad
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[@stdlib/string/right-pad]: https://github.com/stdlib-js/string/tree/main/right-pad
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<!-- </related-links> -->
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</section>
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<!-- /.links -->
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