225 lines
4.8 KiB
Markdown
225 lines
4.8 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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# startsWith
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> Test if a string starts with the characters of another string.
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<section class="intro">
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</section>
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<!-- /.intro -->
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<section class="usage">
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## Usage
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```javascript
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var startsWith = require( '@stdlib/string/starts-with' );
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```
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#### startsWith( str, search\[, position] )
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Tests if a `string` starts with the characters of another `string`.
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```javascript
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var str = 'To be, or not to be, that is the question.';
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var bool = startsWith( str, 'To be' );
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// returns true
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bool = startsWith( str, 'to be' );
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// returns false
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```
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By default, the function searches from the beginning of the input `string`. To search from a different character index, provide a `position` value (zero-based). If provided a negative `position`, the start index is determined relative to the string end (`pos = str.length + position`).
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```javascript
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var str = 'Remember the story I used to tell you when you were a boy?';
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var bool = startsWith( str, 'the story' );
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// returns false
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bool = startsWith( str, 'the story', 9 );
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// returns true
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bool = startsWith( str, 'you', -15 );
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// returns true
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```
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If provided an empty `search` string, the function **always** returns `true`.
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```javascript
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var str = 'beep boop';
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var bool = startsWith( str, '' );
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// returns true
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```
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</section>
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<!-- /.usage -->
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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 startsWith = require( '@stdlib/string/starts-with' );
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var bool;
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var str;
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str = 'Fair is foul, and foul is fair, hover through fog and filthy air';
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bool = startsWith( str, 'Fair' );
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// returns true
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bool = startsWith( str, 'fair' );
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// returns false
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bool = startsWith( str, 'foul', 8 );
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// returns true
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bool = startsWith( str, 'filthy', -10 );
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// returns true
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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: starts-with [options] --search=<string> [<string>]
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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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--search string Search string.
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--pos int Search position.
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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 $'Hello, World!\nBeep Boop Baz' | starts-with --search=Beep --split /\r?\n/
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# Escaped...
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$ echo -n $'Hello, World!\nBeep Boop Baz' | starts-with --search=Beep --split /\\r?\\n/
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```
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- The implementation ignores trailing delimiters.
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</section>
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</section>
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<!-- /.notes -->
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<section class="examples">
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### Examples
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```bash
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$ starts-with --search=be beep
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true
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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 'boop' | starts-with --search=bo
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true
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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 'Hello, World!\tBeep Boop' | starts-with --search=Beep --split '\t'
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false
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true
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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/ends-with`][@stdlib/string/ends-with]</span><span class="delimiter">: </span><span class="description">test if a string ends with the characters of another 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/ends-with]: https://github.com/stdlib-js/string/tree/main/ends-with
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<!-- </related-links> -->
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</section>
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<!-- /.links -->
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