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<HTML><HEAD><TITLE>Recipe 2.7. Generating Random Numbers (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="1999-07-02T01:30:09Z"><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="ch02_01.htm"TITLE="2. Numbers"><LINKREL="prev"HREF="ch02_07.htm"TITLE="2.6. Working with Roman Numerals"><LINKREL="next"HREF="ch02_09.htm"TITLE="2.8. Generating Different Random Numbers"></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="ch02_07.htm"TITLE="2.6. Working with Roman Numerals"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 2.6. Working with Roman Numerals"BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="228"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1"><ACLASS="chapter"REL="up"HREF="ch02_01.htm"TITLE="2. Numbers"></A></FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch02_09.htm"TITLE="2.8. Generating Different Random Numbers"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 2.8. Generating Different Random Numbers"BORDER="0"></A></TD></TR></TABLE></DIV><DIVCLASS="sect1"><H2CLASS="sect1"><ACLASS="title"NAME="ch02-29980">2.7. Generating Random Numbers</A></H2><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch02-pgfId-525">Problem <ACLASS="indexterm"NAME="ch02-idx-1000008031-0"></A><ACLASS="indexterm"NAME="ch02-idx-1000008031-1"></A><ACLASS="indexterm"NAME="ch02-idx-1000008031-2"></A></A></H3><PCLASS="para">You want to make random numbers in a given range, inclusive, such as when you randomly pick an array index, simulate rolling a die in a game of chance, or generate a random password.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch02-pgfId-531">Solution</A></H3><PCLASS="para">Use Perl's <CODECLASS="literal">rand</CODE> function.</P><PRECLASS="programlisting">$random = int( rand( $Y-$X+1 ) ) + $X;</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch02-pgfId-539">Discussion</A></H3><PCLASS="para">This code generates and prints a random integer between 25 and 75, inclusive:</P><PRECLASS="programlisting">$random = int( rand(51)) + 25;print "$random\n";</PRE><PCLASS="para">The <CODECLASS="literal">rand</CODE> function returns a fractional number, from (and including) 0 up to (but not including) its argument. We give it an argument of 51 to get a number that can be 0 or more, but never 51 or more. We take the integer portion of this to get a number from 0 to 50, inclusive (50.99999.... will be turned to 50 by <CODECLASS="literal">int</CODE>). We then add 25 to it, to get a number from 25 to 75, inclusive.</P><PCLASS="para"><ACLASS="indexterm"NAME="ch02-idx-1000008037-0"></A>A common application of this is the random selection of an element from an array:</P><PRECLASS="programlisting">$elt = $array[ rand @array ];</PRE><PCLASS="para">And generating a random <ACLASS="indexterm"NAME="ch02-idx-1000008038-0"></A>password from a sequence of characters:</P><PRECLASS="programlisting">@chars = ( "A" .. "Z", "a" .. "z", 0 .. 9, qw(! @ $ % ^ & *) );$password = join("", @chars[ map { rand @chars } ( 1 .. 8 ) ]);</PRE><PCLASS="para">We use <CODECLASS="literal">map</CODE> to generate eight random indices into <CODECLASS="literal">@chars</CODE>, extract the corresponding characters with a slice, and join them together to form the random password. This isn't a <EMCLASS="emphasis">good</EM> random number, though, as its security relies on the choice of seed, which is based on the time the program started. See <ACLASS="xref"HREF="ch02_09.htm"TITLE="Generating Different Random Numbers">Recipe 2.8</A> for a way to better seed your random number generator.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch02-pgfId-563">See Also</A></H3><PCLASS="para">The <CODECLASS="literal">int</CODE>, <CODECLASS="literal">rand</CODE>, <CODECLASS="literal">map</CODE>, and <CODECLASS="literal">join</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 explore random numbers further in Recipes <ACLASS="xref"HREF="ch02_09.htm"TITLE="Generating Different Random Numbers">Recipe 2.8</A>, <ACLASS="xref"HREF="ch02_10.htm"TITLE="Making Numbers Even More Random">Recipe 2.9</A>, and <ACLASS="xref"HREF="ch02_11.htm"TITLE="Generating Biased Random Numbers">Recipe 2.10</A>; we use random numbers in <ACLASS="xref"HREF="ch01_10.htm"TITLE="Controlling Case">Recipe 1.9</A> <ACLASS="indexterm"NAME="ch02-idx-1000008033-0"></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="ch02_07.htm"TITLE="2.6. 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