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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><meta name="viewport" content="width=device-width, initial-scale=0.8"/><title>8.1 Varieties of Ports</title><link rel="stylesheet" type="text/css" href="../scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="../racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-style.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../doc-site.css" title="default"/><script type="text/javascript" src="../scribble-common.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../doc-site.js"></script><script type="text/javascript" src="../local-redirect/local-redirect.js"></script><script type="text/javascript" src="../local-redirect/local-user-redirect.js"></script><!--[if IE 6]><style type="text/css">.SIEHidden { overflow: hidden; }</style><![endif]--></head><body id="doc-racket-lang-org"><div class="tocset"><div class="tocview"><div class="tocviewlist tocviewlisttopspace"><div class="tocviewtitle"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_0");">►</a></td><td></td><td><a href="index.html" class="tocviewlink" data-pltdoc="x">The Racket Guide</a></td></tr></table></div><div class="tocviewsublisttop" style="display: none;" id="tocview_0"><table cellspacing="0" cellpadding="0"><tr><td align="right">1 </td><td><a href="intro.html" class="tocviewlink" data-pltdoc="x">Welcome to Racket</a></td></tr><tr><td align="right">2 </td><td><a href="to-scheme.html" class="tocviewlink" data-pltdoc="x">Racket Essentials</a></td></tr><tr><td align="right">3 </td><td><a href="datatypes.html" class="tocviewlink" data-pltdoc="x">Built-<wbr></wbr>In Datatypes</a></td></tr><tr><td align="right">4 </td><td><a href="scheme-forms.html" class="tocviewlink" data-pltdoc="x">Expressions and Definitions</a></td></tr><tr><td align="right">5 </td><td><a href="define-struct.html" class="tocviewlink" data-pltdoc="x">Programmer-<wbr></wbr>Defined Datatypes</a></td></tr><tr><td align="right">6 </td><td><a href="modules.html" class="tocviewlink" data-pltdoc="x">Modules</a></td></tr><tr><td align="right">7 </td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">8 </td><td><a href="i_o.html" class="tocviewselflink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">9 </td><td><a href="regexp.html" class="tocviewlink" data-pltdoc="x">Regular Expressions</a></td></tr><tr><td align="right">10 </td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Exceptions and Control</a></td></tr><tr><td align="right">11 </td><td><a href="for.html" class="tocviewlink" data-pltdoc="x">Iterations and Comprehensions</a></td></tr><tr><td align="right">12 </td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">13 </td><td><a href="classes.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">14 </td><td><a href="units.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">15 </td><td><a href="reflection.html" class="tocviewlink" data-pltdoc="x">Reflection and Dynamic Evaluation</a></td></tr><tr><td align="right">16 </td><td><a href="macros.html" class="tocviewlink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">17 </td><td><a href="languages.html" class="tocviewlink" data-pltdoc="x">Creating Languages</a></td></tr><tr><td align="right">18 </td><td><a href="concurrency.html" class="tocviewlink" data-pltdoc="x">Concurrency and Synchronization</a></td></tr><tr><td align="right">19 </td><td><a href="performance.html" class="tocviewlink" data-pltdoc="x">Performance</a></td></tr><tr><td align="right">20 </td><td><a href="parallelism.html" class="tocviewlink" data-pltdoc="x">Parallelism</a></td></tr><tr><td align="right">21 </td><td><a href="running.html" class="tocviewlink" data-pltdoc="x">Running and Creating Executables</a></td></tr><tr><td align="right">22 </td><td><a href="More_Libraries.html" class="tocviewlink" data-pltdoc="x">More Libraries</a></td></tr><tr><td align="right">23 </td><td><a href="dialects.html" class="tocviewlink" data-pltdoc="x">Dialects of Racket and Scheme</a></td></tr><tr><td align="right">24 </td><td><a href="other-editors.html" class="tocviewlink" data-pltdoc="x">Command-<wbr></wbr>Line Tools and Your Editor of Choice</a></td></tr><tr><td align="right"></td><td><a href="doc-bibliography.html" class="tocviewlink" data-pltdoc="x">Bibliography</a></td></tr><tr><td align="right"></td><td><a href="doc-index.html" class="tocviewlink" data-pltdoc="x">Index</a></td></tr></table></div></div><div class="tocviewlist"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_1");">▼</a></td><td>8 </td><td><a href="i_o.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr></table><div class="tocviewsublistbottom" style="display: block;" id="tocview_1"><table cellspacing="0" cellpadding="0"><tr><td align="right">8.1 </td><td><a href="ports.html" class="tocviewselflink" data-pltdoc="x">Varieties of Ports</a></td></tr><tr><td align="right">8.2 </td><td><a href="default-ports.html" class="tocviewlink" data-pltdoc="x">Default Ports</a></td></tr><tr><td align="right">8.3 </td><td><a href="read-write.html" class="tocviewlink" data-pltdoc="x">Reading and Writing Racket Data</a></td></tr><tr><td align="right">8.4 </td><td><a href="serialization.html" class="tocviewlink" data-pltdoc="x">Datatypes and Serialization</a></td></tr><tr><td align="right">8.5 </td><td><a href="encodings.html" class="tocviewlink" data-pltdoc="x">Bytes, Characters, and Encodings</a></td></tr><tr><td align="right">8.6 </td><td><a href="io-patterns.html" class="tocviewlink" data-pltdoc="x">I/<span class="mywbr"> </span>O Patterns</a></td></tr></table></div></div></div></div><div class="maincolumn"><div class="main"><div class="navsettop"><span class="navleft"><form class="searchform"><input class="searchbox" id="searchbox" type="text" tabindex="1" placeholder="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "8.6", "../");"/></form> <a href="https://docs.racket-lang.org/index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("8.6");">top</a><span class="tocsettoggle"> <a href="javascript:void(0);" title="show/hide table of contents" onclick="TocsetToggle();">contents</a></span></span><span class="navright"> <a href="i_o.html" title="backward to "8 Input and Output"" data-pltdoc="x">← prev</a> <a href="i_o.html" title="up to "8 Input and Output"" data-pltdoc="x">up</a> <a href="default-ports.html" title="forward to "8.2 Default Ports"" data-pltdoc="x">next →</a></span> </div><h4 x-source-module="(lib "scribblings/guide/guide.scrbl")" x-source-pkg="racket-doc" x-part-tag=""ports"">8.1<tt> </tt><a name="(part._ports)"></a>Varieties of Ports</h4><p>Various functions create various kinds of ports. Here are a few
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examples:</p><ul><li><p><span style="font-weight: bold">Files:</span> The <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=file-ports.html%23%2528def._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._open-output-file%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">open-output-file</a></span> function opens a
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file for writing, and <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=file-ports.html%23%2528def._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._open-input-file%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">open-input-file</a></span> opens a file for
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reading.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=define.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._define%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">out</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=file-ports.html%23%2528def._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._open-output-file%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">open-output-file</a></span><span class="hspace"> </span><span class="RktVal">"data"</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Writing.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._display%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">display</a></span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="hspace"> </span><span class="RktSym">out</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=port-ops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._close-output-port%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">close-output-port</a></span><span class="hspace"> </span><span class="RktSym">out</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=define.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._define%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">in</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=file-ports.html%23%2528def._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._open-input-file%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">open-input-file</a></span><span class="hspace"> </span><span class="RktVal">"data"</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-line%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">read-line</a></span><span class="hspace"> </span><span class="RktSym">in</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"hello"</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=port-ops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._close-input-port%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">close-input-port</a></span><span class="hspace"> </span><span class="RktSym">in</span><span class="RktPn">)</span></td></tr></table></blockquote></div></p><p>If a file exists already, then <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=file-ports.html%23%2528def._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._open-output-file%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">open-output-file</a></span> raises an
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exception by default. Supply an option like <span class="RktPn">#:exists</span><span class="stt"> </span><span class="RktVal">'</span><span class="RktVal">truncate</span> or <span class="RktPn">#:exists</span><span class="stt"> </span><span class="RktVal">'</span><span class="RktVal">update</span> to re-write or update the
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file:</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=define.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._define%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">out</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=file-ports.html%23%2528def._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._open-output-file%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">open-output-file</a></span><span class="hspace"> </span><span class="RktVal">"data"</span><span class="hspace"> </span><span class="RktPn">#:exists</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">truncate</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Writing.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._display%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">display</a></span><span class="hspace"> </span><span class="RktVal">"howdy"</span><span class="hspace"> </span><span class="RktSym">out</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=port-ops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._close-output-port%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">close-output-port</a></span><span class="hspace"> </span><span class="RktSym">out</span><span class="RktPn">)</span></td></tr></table></blockquote></div></p><p>Instead of having to match the open calls with close calls, most Racket
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programmers will use the <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=file-ports.html%23%2528def._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._call-with-input-file%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">call-with-input-file</a></span> and
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<span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=file-ports.html%23%2528def._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._call-with-output-file%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">call-with-output-file</a></span> functions which take a function to call to carry
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out the desired operation. This function gets as its only argument the port,
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which is automatically opened and closed for the operation.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=file-ports.html%23%2528def._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._call-with-output-file%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">call-with-output-file</a></span><span class="hspace"> </span><span class="RktVal">"data"</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">#:exists</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">truncate</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=lambda.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._lambda%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">out</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Writing.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._display%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">display</a></span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="hspace"> </span><span class="RktSym">out</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=file-ports.html%23%2528def._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._call-with-input-file%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">call-with-input-file</a></span><span class="hspace"> </span><span class="RktVal">"data"</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=lambda.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._lambda%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">in</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-line%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">read-line</a></span><span class="hspace"> </span><span class="RktSym">in</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">"hello"</span></p></td></tr></table></blockquote></div></p></li><li><p><span style="font-weight: bold">Strings:</span> The <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=stringport.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._open-output-string%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">open-output-string</a></span> function creates
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a port that accumulates data into a string, and <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=stringport.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._get-output-string%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">get-output-string</a></span>
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extracts the accumulated string. The <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=stringport.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._open-input-string%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">open-input-string</a></span> function
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creates a port to read from a string.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=define.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._define%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">p</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=stringport.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._open-output-string%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">open-output-string</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Writing.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._display%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">display</a></span><span class="hspace"> </span><span class="RktVal">"hello"</span><span class="hspace"> </span><span class="RktSym">p</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=stringport.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._get-output-string%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">get-output-string</a></span><span class="hspace"> </span><span class="RktSym">p</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"hello"</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-line%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">read-line</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=stringport.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._open-input-string%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">open-input-string</a></span><span class="hspace"> </span><span class="RktVal">"goodbye\nfarewell"</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"goodbye"</span></p></td></tr></table></blockquote></div></p></li><li><p><span style="font-weight: bold">TCP Connections:</span> The <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=tcp.html%23%2528def._%2528%2528lib._racket%252Ftcp..rkt%2529._tcp-connect%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">tcp-connect</a></span> function
|
|
creates both an input port and an output port for the client side of
|
|
a TCP communication. The <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=tcp.html%23%2528def._%2528%2528lib._racket%252Ftcp..rkt%2529._tcp-listen%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">tcp-listen</a></span> function creates a
|
|
server, which accepts connections via <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=tcp.html%23%2528def._%2528%2528lib._racket%252Ftcp..rkt%2529._tcp-accept%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">tcp-accept</a></span>.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=define.html%23%2528form._%2528%2528lib._racket%252Fprivate%252Fbase..rkt%2529._define%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">server</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=tcp.html%23%2528def._%2528%2528lib._racket%252Ftcp..rkt%2529._tcp-listen%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">tcp-listen</a></span><span class="hspace"> </span><span class="RktVal">12345</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=define.html%23%2528form._%2528%2528quote._%7E23%7E25kernel%2529._define-values%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">define-values</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">c-in</span><span class="hspace"> </span><span class="RktSym">c-out</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=tcp.html%23%2528def._%2528%2528lib._racket%252Ftcp..rkt%2529._tcp-connect%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">tcp-connect</a></span><span class="hspace"> </span><span class="RktVal">"localhost"</span><span class="hspace"> </span><span class="RktVal">12345</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=define.html%23%2528form._%2528%2528quote._%7E23%7E25kernel%2529._define-values%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">define-values</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">s-in</span><span class="hspace"> </span><span class="RktSym">s-out</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=tcp.html%23%2528def._%2528%2528lib._racket%252Ftcp..rkt%2529._tcp-accept%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">tcp-accept</a></span><span class="hspace"> </span><span class="RktSym">server</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Writing.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._display%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">display</a></span><span class="hspace"> </span><span class="RktVal">"hello\n"</span><span class="hspace"> </span><span class="RktSym">c-out</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=port-ops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._close-output-port%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">close-output-port</a></span><span class="hspace"> </span><span class="RktSym">c-out</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-line%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">read-line</a></span><span class="hspace"> </span><span class="RktSym">s-in</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"hello"</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-line%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">read-line</a></span><span class="hspace"> </span><span class="RktSym">s-in</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#<eof></span></p></td></tr></table></blockquote></div></p></li><li><p><span style="font-weight: bold">Process Pipes:</span> The <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=subprocess.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._subprocess%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">subprocess</a></span> function runs a new
|
|
process at the OS level and returns ports that correspond to the
|
|
subprocess’s stdin, stdout, and stderr. (The first three arguments
|
|
can be certain kinds of existing ports to connect directly to the
|
|
subprocess, instead of creating new ports.)</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=define.html%23%2528form._%2528%2528quote._%7E23%7E25kernel%2529._define-values%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">define-values</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">p</span><span class="hspace"> </span><span class="RktSym">stdout</span><span class="hspace"> </span><span class="RktSym">stdin</span><span class="hspace"> </span><span class="RktSym">stderr</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=subprocess.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._subprocess%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">subprocess</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="hspace"> </span><span class="RktVal">"/usr/bin/wc"</span><span class="hspace"> </span><span class="RktVal">"-w"</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Writing.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._display%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">display</a></span><span class="hspace"> </span><span class="RktVal">"a b c\n"</span><span class="hspace"> </span><span class="RktSym">stdin</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=port-ops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._close-output-port%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">close-output-port</a></span><span class="hspace"> </span><span class="RktSym">stdin</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-line%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">read-line</a></span><span class="hspace"> </span><span class="RktSym">stdout</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">" </span><span class="hspace"> </span><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes"></span><span class="hspace"> </span><span class="RktRes">3"</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=port-ops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._close-input-port%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">close-input-port</a></span><span class="hspace"> </span><span class="RktSym">stdout</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=port-ops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._close-input-port%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">close-input-port</a></span><span class="hspace"> </span><span class="RktSym">stderr</span><span class="RktPn">)</span></td></tr></table></blockquote></div></p></li><li><p><span style="font-weight: bold">Internal Pipes:</span> The <span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=pipeports.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._make-pipe%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">make-pipe</a></span> function returns
|
|
two ports that are ends of a pipe. This kind of pipe is internal to
|
|
Racket, and not related to OS-level pipes for communicating between
|
|
different processes.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=define.html%23%2528form._%2528%2528quote._%7E23%7E25kernel%2529._define-values%2529%2529&version=8.6" class="RktStxLink Sq" data-pltdoc="x">define-values</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">in</span><span class="hspace"> </span><span class="RktSym">out</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=pipeports.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._make-pipe%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">make-pipe</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Writing.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._display%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">display</a></span><span class="hspace"> </span><span class="RktVal">"garbage"</span><span class="hspace"> </span><span class="RktSym">out</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=port-ops.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._close-output-port%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">close-output-port</a></span><span class="hspace"> </span><span class="RktSym">out</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="https://download.racket-lang.org/releases/8.6/doc/local-redirect/index.html?doc=reference&rel=Byte_and_String_Input.html%23%2528def._%2528%2528quote._%7E23%7E25kernel%2529._read-line%2529%2529&version=8.6" class="RktValLink Sq" data-pltdoc="x">read-line</a></span><span class="hspace"> </span><span class="RktSym">in</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">"garbage"</span></p></td></tr></table></blockquote></div></p></li></ul><div class="navsetbottom"><span class="navleft"><form class="searchform"><input class="searchbox" id="searchbox" type="text" tabindex="1" placeholder="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "8.6", "../");"/></form> <a href="https://docs.racket-lang.org/index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("8.6");">top</a><span class="tocsettoggle"> <a href="javascript:void(0);" title="show/hide table of contents" onclick="TocsetToggle();">contents</a></span></span><span class="navright"> <a href="i_o.html" title="backward to "8 Input and Output"" data-pltdoc="x">← prev</a> <a href="i_o.html" title="up to "8 Input and Output"" data-pltdoc="x">up</a> <a href="default-ports.html" title="forward to "8.2 Default Ports"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html> |