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<HTML><HEAD><TITLE>Recipe 3.10. Short Sleeps (Perl Cookbook)</TITLE><METANAME="DC.title"CONTENT="Perl Cookbook"><METANAME="DC.creator"CONTENT="Tom Christiansen & Nathan Torkington"><METANAME="DC.publisher"CONTENT="O'Reilly & Associates, Inc."><METANAME="DC.date"CONTENT="1999-07-02T01:30:47Z"><METANAME="DC.type"CONTENT="Text.Monograph"><METANAME="DC.format"CONTENT="text/html"SCHEME="MIME"><METANAME="DC.source"CONTENT="1-56592-243-3"SCHEME="ISBN"><METANAME="DC.language"CONTENT="en-US"><METANAME="generator"CONTENT="Jade 1.1/O'Reilly DocBook 3.0 to HTML 4.0"><LINKREV="made"HREF="mailto:online-books@oreilly.com"TITLE="Online Books Comments"><LINKREL="up"HREF="ch03_01.htm"TITLE="3. Dates and Times"><LINKREL="prev"HREF="ch03_10.htm"TITLE="3.9. High-Resolution Timers"><LINKREL="next"HREF="ch03_12.htm"TITLE="3.11. Program: hopdelta"></HEAD><BODYBGCOLOR="#FFFFFF"><img alt="Book Home" border="0" src="gifs/smbanner.gif" usemap="#banner-map" /><map name="banner-map"><area shape="rect" coords="1,-2,616,66" href="index.htm" alt="Perl Cookbook"><area shape="rect" coords="629,-11,726,25" href="jobjects/fsearch.htm" alt="Search this book" /></map><div class="navbar"><p><TABLEWIDTH="684"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch03_10.htm"TITLE="3.9. High-Resolution Timers"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 3.9. High-Resolution Timers"BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="228"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1"><ACLASS="chapter"REL="up"HREF="ch03_01.htm"TITLE="3. Dates and Times"></A></FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch03_12.htm"TITLE="3.11. Program: hopdelta"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 3.11. Program: hopdelta"BORDER="0"></A></TD></TR></TABLE></DIV><DIVCLASS="sect1"><H2CLASS="sect1"><ACLASS="title"NAME="ch03-41241">3.10. Short Sleeps</A></H2><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch03-pgfId-914">Problem <ACLASS="indexterm"NAME="ch03-idx-1000006362-0"></A><ACLASS="indexterm"NAME="ch03-idx-1000006362-1"></A><ACLASS="indexterm"NAME="ch03-idx-1000006362-2"></A><ACLASS="indexterm"NAME="ch03-idx-1000006362-3"></A><ACLASS="indexterm"NAME="ch03-idx-1000006362-4"></A></A></H3><PCLASS="para">You need to sleep for less than a second.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch03-pgfId-920">Solution</A></H3><PCLASS="para">Use the <CODECLASS="literal">select()</CODE> function, if your system supports it:</P><PRECLASS="programlisting">select(undef, undef, undef, $time_to_sleep);</PRE><PCLASS="para">Some systems don't support a four-argument <CODECLASS="literal">select</CODE>. The Time::HiRes module provides a sleep function that takes a floating point number of seconds:</P><PRECLASS="programlisting">use Time::HiRes qw(sleep);sleep($time_to_sleep);</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch03-pgfId-934">Discussion</A></H3><PCLASS="para">Here's an example of <CODECLASS="literal">select</CODE>. It's a simpler version of the program in <ACLASS="xref"HREF="ch01_06.htm"TITLE="Processing a String One Character at a Time">Recipe 1.5</A>. Think of it as your very own 300-baud terminal.</P><PRECLASS="programlisting">while (<>) { select(undef, undef, undef, 0.25); print;}</PRE><PCLASS="para">Using Time::HiRes, we'd write it as:</P><PRECLASS="programlisting">use Time::HiRes qw(sleep);while (<>) { sleep(0.25); print;}</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch03-pgfId-1000006167">See Also</A></H3><PCLASS="para">The documentation for the CPAN modules Time::HiRes and BenchMark; the <CODECLASS="literal">sleep</CODE> and <CODECLASS="literal">select</CODE> functions in <EMCLASS="emphasis">perlfunc </EM>(1) and <ACLASS="olink"HREF="../prog/ch03_01.htm">Chapter 3</A> of <ACLASS="citetitle"HREF="../prog/index.htm"TITLE="Programming Perl"><CITECLASS="citetitle">Programming Perl</CITE></A>; we use the <CODECLASS="literal">select</CODE> function for short sleeps in the <CODECLASS="literal">slowcat</CODE> program in <ACLASS="xref"HREF="ch01_06.htm"TITLE="Processing a String One Character at a Time">Recipe 1.5</A></P></DIV></DIV><DIVCLASS="htmlnav"><P></P><HRALIGN="LEFT"WIDTH="684"TITLE="footer"><TABLEWIDTH="684"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch03_10.htm"TITLE="3.9. 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