341 lines
14 KiB
Plaintext
341 lines
14 KiB
Plaintext
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<meta http-eqiv="content-type" content="text/html;charset=utf-8">
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<title>Go by Example: Regular Expressions</title>
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<div class="example" id="regular-expressions">
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<h2><a href="./">Go by Example</a>: Regular Expressions</h2>
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<table>
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<td class="docs">
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<p>Go offers built-in support for <a href="http://en.wikipedia.org/wiki/Regular_expression">regular expressions</a>.
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Here are some examples of common regexp-related tasks
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in Go.</p>
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<a href="http://play.golang.org/p/7bnr2EXlxK"><img title="Run code" src="play.png" class="run" /></a>
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<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
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</pre></div>
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<td class="code leading">
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<div class="highlight"><pre><span class="kn">import</span> <span class="s">"bytes"</span>
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<span class="kn">import</span> <span class="s">"fmt"</span>
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<span class="kn">import</span> <span class="s">"regexp"</span>
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</pre></div>
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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
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</pre></div>
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</td>
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<td class="docs">
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<p>This tests whether a pattern matches a string.</p>
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<div class="highlight"><pre> <span class="nx">match</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">regexp</span><span class="p">.</span><span class="nx">MatchString</span><span class="p">(</span><span class="s">"p([a-z]+)ch"</span><span class="p">,</span> <span class="s">"peach"</span><span class="p">)</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">match</span><span class="p">)</span>
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</pre></div>
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</td>
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<td class="docs">
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<p>Above we used a string pattern directly, but for
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other regexp tasks you’ll need to <code>Compile</code> an
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optimized <code>Regexp</code> struct.</p>
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<div class="highlight"><pre> <span class="nx">r</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">regexp</span><span class="p">.</span><span class="nx">Compile</span><span class="p">(</span><span class="s">"p([a-z]+)ch"</span><span class="p">)</span>
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</pre></div>
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<td class="docs">
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<p>Many methods are available on these structs. Here’s
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a match test like we saw earlier.</p>
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<td class="code leading">
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<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">r</span><span class="p">.</span><span class="nx">MatchString</span><span class="p">(</span><span class="s">"peach"</span><span class="p">))</span>
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</pre></div>
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<td class="docs">
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<p>This finds the match for the regexp.</p>
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<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">r</span><span class="p">.</span><span class="nx">FindString</span><span class="p">(</span><span class="s">"peach punch"</span><span class="p">))</span>
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</pre></div>
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</td>
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<td class="docs">
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<p>The also finds the first match but returns the
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start and end indexes for the match instead of the
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matching text.</p>
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<td class="code leading">
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<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">r</span><span class="p">.</span><span class="nx">FindStringIndex</span><span class="p">(</span><span class="s">"peach punch"</span><span class="p">))</span>
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</pre></div>
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<td class="docs">
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<p>The <code>Submatch</code> variants include information about
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both the whole-pattern matches and the submatches
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within those matches. For example this will return
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information for both <code>p([a-z]+)ch</code> and <code>([a-z]+)</code>.</p>
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<td class="code leading">
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<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">r</span><span class="p">.</span><span class="nx">FindStringSubmatch</span><span class="p">(</span><span class="s">"peach punch"</span><span class="p">))</span>
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</pre></div>
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<td class="docs">
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<p>Similarly this will return information about the
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indexes of matches and submatches.</p>
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<td class="code leading">
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<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">r</span><span class="p">.</span><span class="nx">FindStringSubmatchIndex</span><span class="p">(</span><span class="s">"peach punch"</span><span class="p">))</span>
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</pre></div>
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<td class="docs">
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<p>The <code>All</code> variants of these functions apply to all
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matches in the input, not just the first. For
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example to find all matches for a regexp.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">r</span><span class="p">.</span><span class="nx">FindAllString</span><span class="p">(</span><span class="s">"peach punch pinch"</span><span class="p">,</span> <span class="o">-</span><span class="mi">1</span><span class="p">))</span>
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</pre></div>
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<td class="docs">
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<p>These <code>All</code> variants are available for the other
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functions we saw above as well.</p>
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<td class="code leading">
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<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">r</span><span class="p">.</span><span class="nx">FindAllStringSubmatchIndex</span><span class="p">(</span>
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<span class="s">"peach punch pinch"</span><span class="p">,</span> <span class="o">-</span><span class="mi">1</span><span class="p">))</span>
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</pre></div>
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<td class="docs">
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<p>Providing a non-negative integer as the second
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argument to these functions will limit the number
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of matches.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">r</span><span class="p">.</span><span class="nx">FindAllString</span><span class="p">(</span><span class="s">"peach punch pinch"</span><span class="p">,</span> <span class="mi">2</span><span class="p">))</span>
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</pre></div>
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</td>
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<td class="docs">
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<p>Our examples above had string arguments and used
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names like <code>MatchString</code>. We can also provide
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<code>[]byte</code> arguments and drop <code>String</code> from the
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function name.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">r</span><span class="p">.</span><span class="nx">Match</span><span class="p">([]</span><span class="nb">byte</span><span class="p">(</span><span class="s">"peach"</span><span class="p">)))</span>
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</pre></div>
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<td class="docs">
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<p>When creating constants with regular expressions
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you can use the <code>MustCompile</code> variation of
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<code>Compile</code>. A plain <code>Compile</code> won’t work for
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constants because it has 2 return values.</p>
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<td class="code leading">
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<div class="highlight"><pre> <span class="nx">r</span> <span class="p">=</span> <span class="nx">regexp</span><span class="p">.</span><span class="nx">MustCompile</span><span class="p">(</span><span class="s">"p([a-z]+)ch"</span><span class="p">)</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">r</span><span class="p">)</span>
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</pre></div>
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<td class="docs">
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<p>The <code>regexp</code> package can also be used to replace
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subsets of strings with other values.</p>
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<td class="code leading">
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<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">r</span><span class="p">.</span><span class="nx">ReplaceAllString</span><span class="p">(</span><span class="s">"a peach"</span><span class="p">,</span> <span class="s">"<fruit>"</span><span class="p">))</span>
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</pre></div>
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<td class="docs">
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<p>The <code>Func</code> variant allows you to transform matched
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text with a given function.</p>
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<td class="code">
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<div class="highlight"><pre> <span class="nx">in</span> <span class="o">:=</span> <span class="p">[]</span><span class="nb">byte</span><span class="p">(</span><span class="s">"a peach"</span><span class="p">)</span>
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<span class="nx">out</span> <span class="o">:=</span> <span class="nx">r</span><span class="p">.</span><span class="nx">ReplaceAllFunc</span><span class="p">(</span><span class="nx">in</span><span class="p">,</span> <span class="nx">bytes</span><span class="p">.</span><span class="nx">ToUpper</span><span class="p">)</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nb">string</span><span class="p">(</span><span class="nx">out</span><span class="p">))</span>
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<span class="p">}</span>
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</pre></div>
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</table>
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<div class="highlight"><pre><span class="gp">$</span> go run regular-expressions.go
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<span class="go">true</span>
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<span class="go">true</span>
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<span class="go">peach</span>
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<span class="go">[0 5]</span>
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<span class="go">[peach ea]</span>
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<span class="go">[0 5 1 3]</span>
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<span class="go">[peach punch pinch]</span>
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<span class="go">[[0 5 1 3] [6 11 7 9] [12 17 13 15]]</span>
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<span class="go">[peach punch]</span>
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<span class="go">true</span>
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<span class="go">p([a-z]+)ch</span>
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<span class="go">a <fruit></span>
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<span class="go">a PEACH</span>
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</pre></div>
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<td class="docs">
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<p>For a complete reference on Go regular expressions check
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the <a href="http://golang.org/pkg/regexp/"><code>regexp</code></a> package docs.</p>
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<td class="code empty">
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</table>
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<p class="next">
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Next example: <a href="json">JSON</a>.
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