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<HTML><HEAD><TITLE>Recipe 2.17. Putting Commas in 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="1999-07-02T01:30:23Z"><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_17.htm"TITLE="2.16. Converting Between Octal and Hexadecimal"><LINKREL="next"HREF="ch02_19.htm"TITLE="2.18. Printing Correct Plurals"></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_17.htm"TITLE="2.16. Converting Between Octal and Hexadecimal"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 2.16. Converting Between Octal and Hexadecimal"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_19.htm"TITLE="2.18. Printing Correct Plurals"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 2.18. Printing Correct Plurals"BORDER="0"></A></TD></TR></TABLE></DIV><DIVCLASS="sect1"><H2CLASS="sect1"><ACLASS="title"NAME="ch02-chap02_putting_0">2.17. Putting Commas in Numbers</A></H2><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch02-pgfId-1297">Problem <ACLASS="indexterm"NAME="ch02-idx-1000008118-0"></A><ACLASS="indexterm"NAME="ch02-idx-1000008118-1"></A><ACLASS="indexterm"NAME="ch02-idx-1000008118-2"></A><ACLASS="indexterm"NAME="ch02-idx-1000008118-3"></A><ACLASS="indexterm"NAME="ch02-idx-1000008118-4"></A><ACLASS="indexterm"NAME="ch02-idx-1000008118-5"></A></A></H3><PCLASS="para">You want to output a number with commas in the right place. People like to see long numbers broken up in this way, especially in reports.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch02-pgfId-1303">Solution</A></H3><PCLASS="para">Reverse the string so you can use backtracking to avoid substitution in the fractional part of the number. Then use a regular expression to find where you need commas, and substitute them in. Finally, reverse the string back.</P><PRECLASS="programlisting">sub commify { my $text = reverse $_[0]; $text =~ s/(\d\d\d)(?=\d)(?!\d*\.)/$1,/g; return scalar reverse $text;}</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch02-pgfId-1319">Discussion</A></H3><PCLASS="para">It's a lot easier in regular expressions to work from the front than from the back. With this in mind, we reverse the string and make a minor change to the algorithm that repeatedly inserts commas three digits from the end. When all insertions are done, we reverse the final string and return it. Because <CODECLASS="literal">reverse</CODE> is sensitive to its implicit return context, we force it to scalar context.</P><PCLASS="para">This function can be easily adjusted to accommodate the use of periods instead of commas, as are used in some countries.</P><PCLASS="para">Here's an example of <CODECLASS="literal">commify</CODE><ACLASS="indexterm"NAME="ch02-idx-1000008122-0"></A> in action:</P><PRECLASS="programlisting"># more reasonable web counter :-)use Math::TrulyRandom;$hits = truly_random_value(); # negative hits!$output = "Your web page received $hits accesses last month.\n";print commify($output);<CODECLASS="userinput"><B><CODECLASS="replaceable"><I>Your web page received -1,740,525,205 accesses last month.</I></CODE></B></CODE></PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch02-pgfId-1000008299">See Also</A></H3><PCLASS="para"><EMCLASS="emphasis">perllocale </EM>(1); the <CODECLASS="literal">reverse</CODE> function 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>; the section "Adding Commas to a Number" in Chapter 7 of <CITECLASS="citetitle">Mastering Regular Expressions</CITE><ACLASS="indexterm"NAME="ch02-idx-1000008560-0"></A><ACLASS="indexterm"NAME="ch02-idx-1000008560-1"></A><ACLASS="indexterm"NAME="ch02-idx-1000008560-2"></A><ACLASS="indexterm"NAME="ch02-idx-1000008560-3"></A><ACLASS="indexterm"NAME="ch02-idx-1000008560-4"></A><ACLASS="indexterm"NAME="ch02-idx-1000008560-5"></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="ch02_17.htm"TITLE="2.16. 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