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| <section id='main' class="content"> |
| <h1 class='fqn'><span class='in-band'>Crate <a class="mod" href=''>env_logger</a></span><span class='out-of-band'><span id='render-detail'> |
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| </span><a class='srclink' href='../src/env_logger/lib.rs.html#11-623' title='goto source code'>[src]</a></span></h1> |
| <div class='docblock'><p>A logger configured via an environment variable which writes to standard |
| error.</p> |
| |
| <h2 id='example' class='section-header'><a href='#example'>Example</a></h2> |
| <pre class="rust rust-example-rendered"> |
| <span class="attribute">#[<span class="ident">macro_use</span>]</span> <span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">log</span>; |
| <span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">env_logger</span>; |
| |
| <span class="kw">use</span> <span class="ident">log</span>::<span class="ident">LogLevel</span>; |
| |
| <span class="kw">fn</span> <span class="ident">main</span>() { |
| <span class="ident">env_logger</span>::<span class="ident">init</span>().<span class="ident">unwrap</span>(); |
| |
| <span class="macro">debug</span><span class="macro">!</span>(<span class="string">"this is a debug {}"</span>, <span class="string">"message"</span>); |
| <span class="macro">error</span><span class="macro">!</span>(<span class="string">"this is printed by default"</span>); |
| |
| <span class="kw">if</span> <span class="macro">log_enabled</span><span class="macro">!</span>(<span class="ident">LogLevel</span>::<span class="ident">Info</span>) { |
| <span class="kw">let</span> <span class="ident">x</span> <span class="op">=</span> <span class="number">3</span> <span class="op">*</span> <span class="number">4</span>; <span class="comment">// expensive computation</span> |
| <span class="macro">info</span><span class="macro">!</span>(<span class="string">"the answer was: {}"</span>, <span class="ident">x</span>); |
| } |
| }</pre> |
| |
| <p>Assumes the binary is <code>main</code>:</p> |
| |
| <pre><code class="language-{.bash}">$ RUST_LOG=error ./main |
| ERROR:main: this is printed by default |
| </code></pre> |
| |
| <pre><code class="language-{.bash}">$ RUST_LOG=info ./main |
| ERROR:main: this is printed by default |
| INFO:main: the answer was: 12 |
| </code></pre> |
| |
| <pre><code class="language-{.bash}">$ RUST_LOG=debug ./main |
| DEBUG:main: this is a debug message |
| ERROR:main: this is printed by default |
| INFO:main: the answer was: 12 |
| </code></pre> |
| |
| <p>You can also set the log level on a per module basis:</p> |
| |
| <pre><code class="language-{.bash}">$ RUST_LOG=main=info ./main |
| ERROR:main: this is printed by default |
| INFO:main: the answer was: 12 |
| </code></pre> |
| |
| <p>And enable all logging:</p> |
| |
| <pre><code class="language-{.bash}">$ RUST_LOG=main ./main |
| DEBUG:main: this is a debug message |
| ERROR:main: this is printed by default |
| INFO:main: the answer was: 12 |
| </code></pre> |
| |
| <p>See the documentation for the log crate for more information about its API.</p> |
| |
| <h2 id='enabling-logging' class='section-header'><a href='#enabling-logging'>Enabling logging</a></h2> |
| <p>Log levels are controlled on a per-module basis, and by default all logging |
| is disabled except for <code>error!</code>. Logging is controlled via the <code>RUST_LOG</code> |
| environment variable. The value of this environment variable is a |
| comma-separated list of logging directives. A logging directive is of the |
| form:</p> |
| |
| <pre><code class="language-text">path::to::module=log_level |
| </code></pre> |
| |
| <p>The path to the module is rooted in the name of the crate it was compiled |
| for, so if your program is contained in a file <code>hello.rs</code>, for example, to |
| turn on logging for this file you would use a value of <code>RUST_LOG=hello</code>. |
| Furthermore, this path is a prefix-search, so all modules nested in the |
| specified module will also have logging enabled.</p> |
| |
| <p>The actual <code>log_level</code> is optional to specify. If omitted, all logging will |
| be enabled. If specified, it must be one of the strings <code>debug</code>, <code>error</code>, |
| <code>info</code>, <code>warn</code>, or <code>trace</code>.</p> |
| |
| <p>As the log level for a module is optional, the module to enable logging for |
| is also optional. If only a <code>log_level</code> is provided, then the global log |
| level for all modules is set to this value.</p> |
| |
| <p>Some examples of valid values of <code>RUST_LOG</code> are:</p> |
| |
| <ul> |
| <li><code>hello</code> turns on all logging for the 'hello' module</li> |
| <li><code>info</code> turns on all info logging</li> |
| <li><code>hello=debug</code> turns on debug logging for 'hello'</li> |
| <li><code>hello,std::option</code> turns on hello, and std's option logging</li> |
| <li><code>error,hello=warn</code> turn on global error logging and also warn for hello</li> |
| </ul> |
| |
| <h2 id='filtering-results' class='section-header'><a href='#filtering-results'>Filtering results</a></h2> |
| <p>A RUST_LOG directive may include a regex filter. The syntax is to append <code>/</code> |
| followed by a regex. Each message is checked against the regex, and is only |
| logged if it matches. Note that the matching is done after formatting the |
| log string but before adding any logging meta-data. There is a single filter |
| for all modules.</p> |
| |
| <p>Some examples:</p> |
| |
| <ul> |
| <li><code>hello/foo</code> turns on all logging for the 'hello' module where the log |
| message includes 'foo'.</li> |
| <li><code>info/f.o</code> turns on all info logging where the log message includes 'foo', |
| 'f1o', 'fao', etc.</li> |
| <li><code>hello=debug/foo*foo</code> turns on debug logging for 'hello' where the log |
| message includes 'foofoo' or 'fofoo' or 'fooooooofoo', etc.</li> |
| <li><code>error,hello=warn/[0-9] scopes</code> turn on global error logging and also |
| warn for hello. In both cases the log message must include a single digit |
| number followed by 'scopes'.</li> |
| </ul> |
| </div><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2> |
| <table> |
| <tr class=' module-item'> |
| <td><a class="struct" href="struct.LogBuilder.html" |
| title='struct env_logger::LogBuilder'>LogBuilder</a></td> |
| <td class='docblock-short'> |
| <p>LogBuilder acts as builder for initializing the Logger. |
| It can be used to customize the log format, change the enviromental variable used |
| to provide the logging directives and also set the default log level filter.</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="struct" href="struct.Logger.html" |
| title='struct env_logger::Logger'>Logger</a></td> |
| <td class='docblock-short'> |
| <p>The logger.</p> |
| </td> |
| </tr></table><h2 id='functions' class='section-header'><a href="#functions">Functions</a></h2> |
| <table> |
| <tr class=' module-item'> |
| <td><a class="fn" href="fn.init.html" |
| title='fn env_logger::init'>init</a></td> |
| <td class='docblock-short'> |
| <p>Initializes the global logger with an env logger.</p> |
| </td> |
| </tr></table></section> |
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