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  <title>ioutil - The Go Programming Language</title>

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  <h1>Package ioutil</h1>


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			<dl>
			<dd><code>import "io/ioutil"</code></dd>
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			<dd><a href="index.html#pkg-overview" class="overviewLink">Overview</a></dd>
			<dd><a href="index.html#pkg-index" class="indexLink">Index</a></dd>
			
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				<p>
Package ioutil implements some I/O utility functions.
</p>

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			<dl>
			
			
				<dd><a href="index.html#pkg-variables">Variables</a></dd>
			
			
				<dd><a href="index.html#NopCloser">func NopCloser(r io.Reader) io.ReadCloser</a></dd>
			
				
				<dd><a href="index.html#ReadAll">func ReadAll(r io.Reader) ([]byte, error)</a></dd>
			
				
				<dd><a href="index.html#ReadDir">func ReadDir(dirname string) ([]os.FileInfo, error)</a></dd>
			
				
				<dd><a href="index.html#ReadFile">func ReadFile(filename string) ([]byte, error)</a></dd>
			
				
				<dd><a href="index.html#TempDir">func TempDir(dir, prefix string) (name string, err error)</a></dd>
			
				
				<dd><a href="index.html#TempFile">func TempFile(dir, prefix string) (f *os.File, err error)</a></dd>
			
				
				<dd><a href="index.html#WriteFile">func WriteFile(filename string, data []byte, perm os.FileMode) error</a></dd>
			
			
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			<h4>Examples</h4>
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			<dd><a class="exampleLink" href="index.html#example_ReadAll">ReadAll</a></dd>
			
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			<h4>Package files</h4>
			<p>
			<span style="font-size:90%">
			
				<a href="http://localhost:6060/src/io/ioutil/ioutil.go">ioutil.go</a>
			
				<a href="http://localhost:6060/src/io/ioutil/tempfile.go">tempfile.go</a>
			
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			  In the call graph viewer below, each node
			  is a function belonging to this package
			  and its children are the functions it
			  calls&mdash;perhaps dynamically.
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			  The root nodes are the entry points of the
			  package: functions that may be called from
			  outside the package.
			  There may be non-exported or anonymous
			  functions among them if they are called
			  dynamically from another package.
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			  Click a node to visit that function's source code.
			  From there you can visit its callers by
			  clicking its declaring <code>func</code>
			  token.
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			  Functions may be omitted if they were
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			  particular programs or tests that were
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			<h2 id="pkg-variables">Variables</h2>
			
				<pre>var <span id="Discard">Discard</span> <a href="../index.html">io</a>.<a href="../index.html#Writer">Writer</a> = devNull(0)</pre>
				<p>
Discard is an io.Writer on which all Write calls succeed
without doing anything.
</p>

			
			<h2 id="NopCloser">func <a href="http://localhost:6060/src/io/ioutil/ioutil.go?s=3643:3684#L112">NopCloser</a></h2>
			<pre>func NopCloser(r <a href="../index.html">io</a>.<a href="../index.html#Reader">Reader</a>) <a href="../index.html">io</a>.<a href="../index.html#ReadCloser">ReadCloser</a></pre>
			<p>
NopCloser returns a ReadCloser with a no-op Close method wrapping
the provided Reader r.
</p>

			
			<h2 id="ReadAll">func <a href="http://localhost:6060/src/io/ioutil/ioutil.go?s=1147:1188#L31">ReadAll</a></h2>
			<pre>func ReadAll(r <a href="../index.html">io</a>.<a href="../index.html#Reader">Reader</a>) ([]<a href="../../builtin/index.html#byte">byte</a>, <a href="../../builtin/index.html#error">error</a>)</pre>
			<p>
ReadAll reads from r until an error or EOF and returns the data it read.
A successful call returns err == nil, not err == EOF. Because ReadAll is
defined to read from src until EOF, it does not treat an EOF from Read
as an error to be reported.
</p>

			<div id="example_ReadAll" class="toggle">
	<div class="collapsed">
		<p class="exampleHeading toggleButton">▹ <span class="text">Example</span></p>
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	<div class="expanded">
		<p class="exampleHeading toggleButton">▾ <span class="text">Example</span></p>
		
		
			<p>Code:</p>
			<pre class="code">r := strings.NewReader(&#34;Go is a general-purpose language designed with systems programming in mind.&#34;)

b, err := ioutil.ReadAll(r)
if err != nil {
    log.Fatal(err)
}

fmt.Printf(&#34;%s&#34;, b)

<span class="comment"></pre>
			
			<p>Output:</p>
			<pre class="output">Go is a general-purpose language designed with systems programming in mind.
</pre>
			
		
	</div>
</div>

			
			<h2 id="ReadDir">func <a href="http://localhost:6060/src/io/ioutil/ioutil.go?s=3220:3271#L90">ReadDir</a></h2>
			<pre>func ReadDir(dirname <a href="../../builtin/index.html#string">string</a>) ([]<a href="../../os/index.html">os</a>.<a href="../../os/index.html#FileInfo">FileInfo</a>, <a href="../../builtin/index.html#error">error</a>)</pre>
			<p>
ReadDir reads the directory named by dirname and returns
a list of directory entries sorted by filename.
</p>

			<div id="example_ReadDir" class="toggle">
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		<p class="exampleHeading toggleButton">▹ <span class="text">Example</span></p>
	</div>
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		<p class="exampleHeading toggleButton">▾ <span class="text">Example</span></p>
		
		
			<p>Code:</p>
			<pre class="code">
files, err := ioutil.ReadDir(&#34;.&#34;)
if err != nil {
    log.Fatal(err)
}

for _, file := range files {
    fmt.Println(file.Name())
}
</pre>
			
		
	</div>
</div>

			
			<h2 id="ReadFile">func <a href="http://localhost:6060/src/io/ioutil/ioutil.go?s=1464:1510#L39">ReadFile</a></h2>
			<pre>func ReadFile(filename <a href="../../builtin/index.html#string">string</a>) ([]<a href="../../builtin/index.html#byte">byte</a>, <a href="../../builtin/index.html#error">error</a>)</pre>
			<p>
ReadFile reads the file named by filename and returns the contents.
A successful call returns err == nil, not err == EOF. Because ReadFile
reads the whole file, it does not treat an EOF from Read as an error
to be reported.
</p>

			
			<h2 id="TempDir">func <a href="http://localhost:6060/src/io/ioutil/tempfile.go?s=2143:2200#L66">TempDir</a></h2>
			<pre>func TempDir(dir, prefix <a href="../../builtin/index.html#string">string</a>) (name <a href="../../builtin/index.html#string">string</a>, err <a href="../../builtin/index.html#error">error</a>)</pre>
			<p>
TempDir creates a new temporary directory in the directory dir
with a name beginning with prefix and returns the path of the
new directory.  If dir is the empty string, TempDir uses the
default directory for temporary files (see os.TempDir).
Multiple programs calling TempDir simultaneously
will not choose the same directory.  It is the caller&#39;s responsibility
to remove the directory when no longer needed.
</p>

			<div id="example_TempDir" class="toggle">
	<div class="collapsed">
		<p class="exampleHeading toggleButton">▹ <span class="text">Example</span></p>
	</div>
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		<p class="exampleHeading toggleButton">▾ <span class="text">Example</span></p>
		
		
			<p>Code:</p>
			<pre class="code">
content := []byte(&#34;temporary file&#39;s content&#34;)
dir, err := ioutil.TempDir(&#34;&#34;, &#34;example&#34;)
if err != nil {
    log.Fatal(err)
}

defer os.RemoveAll(dir) <span class="comment">// clean up</span>

tmpfn := filepath.Join(dir, &#34;tmpfile&#34;)
if err := ioutil.WriteFile(tmpfn, content, 0666); err != nil {
    log.Fatal(err)
}
</pre>
			
		
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</div>

			
			<h2 id="TempFile">func <a href="http://localhost:6060/src/io/ioutil/tempfile.go?s=1288:1345#L37">TempFile</a></h2>
			<pre>func TempFile(dir, prefix <a href="../../builtin/index.html#string">string</a>) (f *<a href="../../os/index.html">os</a>.<a href="../../os/index.html#File">File</a>, err <a href="../../builtin/index.html#error">error</a>)</pre>
			<p>
TempFile creates a new temporary file in the directory dir
with a name beginning with prefix, opens the file for reading
and writing, and returns the resulting *os.File.
If dir is the empty string, TempFile uses the default directory
for temporary files (see os.TempDir).
Multiple programs calling TempFile simultaneously
will not choose the same file.  The caller can use f.Name()
to find the pathname of the file.  It is the caller&#39;s responsibility
to remove the file when no longer needed.
</p>

			<div id="example_TempFile" class="toggle">
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		<p class="exampleHeading toggleButton">▹ <span class="text">Example</span></p>
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	<div class="expanded">
		<p class="exampleHeading toggleButton">▾ <span class="text">Example</span></p>
		
		
			<p>Code:</p>
			<pre class="code">
content := []byte(&#34;temporary file&#39;s content&#34;)
tmpfile, err := ioutil.TempFile(&#34;&#34;, &#34;example&#34;)
if err != nil {
    log.Fatal(err)
}

defer os.Remove(tmpfile.Name()) <span class="comment">// clean up</span>

if _, err := tmpfile.Write(content); err != nil {
    log.Fatal(err)
}
if err := tmpfile.Close(); err != nil {
    log.Fatal(err)
}
</pre>
			
		
	</div>
</div>

			
			<h2 id="WriteFile">func <a href="http://localhost:6060/src/io/ioutil/ioutil.go?s=2520:2588#L66">WriteFile</a></h2>
			<pre>func WriteFile(filename <a href="../../builtin/index.html#string">string</a>, data []<a href="../../builtin/index.html#byte">byte</a>, perm <a href="../../os/index.html">os</a>.<a href="../../os/index.html#FileMode">FileMode</a>) <a href="../../builtin/index.html#error">error</a></pre>
			<p>
WriteFile writes data to a file named by filename.
If the file does not exist, WriteFile creates it with permissions perm;
otherwise WriteFile truncates it before writing.
</p>

			
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