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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 49] Working with Numbers</TITLE><METANAME="DC.title"CONTENT="UNIX Power Tools"><METANAME="DC.creator"CONTENT="Jerry Peek, Tim O'Reilly & Mike Loukides"><METANAME="DC.publisher"CONTENT="O'Reilly & Associates, Inc."><METANAME="DC.date"CONTENT="1998-08-04T21:56:38Z"><METANAME="DC.type"CONTENT="Text.Monograph"><METANAME="DC.format"CONTENT="text/html"SCHEME="MIME"><METANAME="DC.source"CONTENT="1-56592-260-3"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="part09.htm"TITLE="IX. Miscellaneous "><LINKREL="prev"HREF="ch48_12.htm"TITLE="48.12 Using index with a Filter "><LINKREL="next"HREF="ch49_02.htm"TITLE="49.2 bc: Hexadecimal or Binary Conversion "></HEAD><BODYBGCOLOR="#FFFFFF"TEXT="#000000"><DIVCLASS="htmlnav"><H1><IMGSRC="gifs/smbanner.gif"ALT="UNIX Power Tools"USEMAP="#srchmap"BORDER="0"></H1><MAPNAME="srchmap"><AREASHAPE="RECT"COORDS="0,0,466,58"HREF="index.htm"ALT="UNIX Power Tools"><AREASHAPE="RECT"COORDS="467,0,514,18"HREF="jobjects/fsearch.htm"ALT="Search this book"></MAP><TABLEWIDTH="515"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch48_12.htm"TITLE="48.12 Using index with a Filter "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 48.12 Using index with a Filter "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 49</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch49_02.htm"TITLE="49.2 bc: Hexadecimal or Binary Conversion "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 49.2 bc: Hexadecimal or Binary Conversion "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="CHAPTER"><H1CLASS="chapter"><ACLASS="title"NAME="UPT-CHP-49">49. Working with Numbers</A></H1><DIVCLASS="htmltoc"><P><B>Contents:</B><BR><ACLASS="sect1"HREF="#UPT-ART-3920"TITLE="49.1 bc: Simple Math at the Shell Prompt ">bc: Simple Math at the Shell Prompt </A><BR><ACLASS="sect1"HREF="ch49_02.htm"TITLE="49.2 bc: Hexadecimal or Binary Conversion ">bc: Hexadecimal or Binary Conversion </A><BR><ACLASS="sect1"HREF="ch49_03.htm"TITLE="49.3 Gotchas in Base Conversion ">Gotchas in Base Conversion </A><BR><ACLASS="sect1"HREF="ch49_04.htm"TITLE="49.4 bc's Sine and Cosine Are in Radians ">bc's Sine and Cosine Are in Radians </A><BR><ACLASS="sect1"HREF="ch49_05.htm"TITLE="49.5 Base Conversion Using cvtbase ">Base Conversion Using cvtbase </A><BR><ACLASS="sect1"HREF="ch49_06.htm"TITLE="49.6 Quick Arithmetic with expr ">Quick Arithmetic with expr </A><BR><ACLASS="sect1"HREF="ch49_07.htm"TITLE="49.7 Total a Column with addup ">Total a Column with addup </A><BR><ACLASS="sect1"HREF="ch49_08.htm"TITLE="49.8 It's Great to Have a Spreadsheet ">It's Great to Have a Spreadsheet </A><BR><ACLASS="sect1"HREF="ch49_09.htm"TITLE="49.9 Business Graphics with ipl ">Business Graphics with ipl </A></P><P></P></DIV><DIVCLASS="sect1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-3920">49.1 bc: Simple Math at the Shell Prompt </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="UPT-ART-3920-IX-NUMBERS-WORKING-WITH"></A><ACLASS="indexterm"NAME="AUTOID-58453"></A><ACLASS="indexterm"NAME="AUTOID-58456"></A><ACLASS="indexterm"NAME="UPT-ART-3920-IX-BC-PROGRAM"></A><ACLASS="indexterm"NAME="AUTOID-58461"></A><ACLASS="indexterm"NAME="AUTOID-58463"></A>Want to do a few simple calculations? Standard UNIX providestwo simple calculators: <EMCLASS="emphasis">dc</EM> (desk calculator) and <EMCLASS="emphasis">bc</EM>.(Who knowswhat the <EMCLASS="emphasis">b</EM> stands for? The manual page refers to it only as "anarbitrary precision arithmetic language.")</P><PCLASS="para">To a novice, <EMCLASS="emphasis">dc</EM> sounds more promising.However, it's areverse-Polish calculator. You enter each operand on aseparate line, followed by an operator. The operands arestored on a stack; the operator pops them from the stack,replacing them with the result. Unfortunately for the novice,the result isn't printed.You need to type <EMCLASS="emphasis">p</EM> ("print") to getany output.</P><PCLASS="para"><EMCLASS="emphasis">bc</EM> is actually much easier to use:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>bc5*2</B></CODE>10<KBDCLASS="keycap">[CTRL-d]</KBD>%</PRE></BLOCKQUOTE></P><PCLASS="para">Simply type an arithmetic expression, followed by a RETURN.The result will be printed to standard output. Type CTRL-d toexit.</P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-58480"></A><ACLASS="indexterm"NAME="AUTOID-58482"></A>The only thing you need to learn to find <EMCLASS="emphasis">bc</EM> really useful isthe <EMCLASS="emphasis">scale</EM> command, which tells the calculator how many decimalplaces to use. The default is 0, so typing an expression like<CODECLASS="literal">10/4</CODE> yields the unfortunate answer 2. However:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>bcscale=210/4</B></CODE>2.50</PRE></BLOCKQUOTE></P><PCLASS="para">gives a more acceptable two decimal places. Scale can be setfrom 0 to 99 decimal places.</P><PCLASS="para">As an alternative, invoke <EMCLASS="emphasis">bc</EM> with the <EMCLASS="emphasis">-l</EM> option, which willautomatically give you up to 20 decimal places worth ofprecision (but a lot of trailing zeros on simple division).</P><PCLASS="para"><EMCLASS="emphasis">bc</EM> is really quite complete - you can even define your ownfunctions.See the <EMCLASS="emphasis">bc</EM> manual page for details.It's also useful for <SPANCLASS="link">base conversion (<ACLASS="linkend"HREF="ch49_02.htm"TITLE="bc: Hexadecimal or Binary Conversion ">49.2</A>)</SPAN>.</P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-58500"></A><ACLASS="indexterm"NAME="AUTOID-58503"></A><EMCLASS="emphasis">expr</EM> can also be used to do<SPANCLASS="link">simple math (<ACLASS="linkend"HREF="ch49_06.htm"TITLE="Quick Arithmetic with expr ">49.6</A>)</SPAN>on the command line,but it's really better suited for <SPANCLASS="link">doing math in shell scripts (<ACLASS="linkend"HREF="ch45_28.htm"TITLE="Quick Reference: expr ">45.28</A>)</SPAN>.</P><PCLASS="para">Of course, if you're running the <SPANCLASS="link">X Window System (<ACLASS="linkend"HREF="ch01_31.htm"TITLE="The X Window System ">1.31</A>)</SPAN>,you can just use <EMCLASS="emphasis">xcalc</EM>, which draws a Texas Instruments or HPcalculator right on the screen, and lets you punch keys on the keyboardor with the mouse.</P><DIVCLASS="sect1info"><PCLASS="SECT1INFO">- <SPANCLASS="authorinitials">TOR</SPAN></P></DIV></DIV></DIV><DIVCLASS="htmlnav"><P></P><HRALIGN="LEFT"WIDTH="515"TITLE="footer"><TABLEWIDTH="515"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch48_12.htm"TITLE="48.12 Using index with a Filter "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 48.12 Using index with a Filter "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><ACLASS="book"HREF="index.htm"TITLE="UNIX Power Tools"><IMGSRC="gifs/txthome.gif"SRC="gifs/txthome.gif"ALT="UNIX Power Tools"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch49_02.htm"TITLE="49.2 bc: Hexadecimal or Binary Conversion "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 49.2 bc: Hexadecimal or Binary Conversion "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">48.12 Using index with a Filter </TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><ACLASS="index"HREF="index/idx_0.htm"TITLE="Book Index"><IMGSRC="gifs/index.gif"SRC="gifs/index.gif"ALT="Book Index"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172">49.2 bc: Hexadecimal or Binary Conversion </TD></TR></TABLE><HRALIGN="LEFT"WIDTH="515"TITLE="footer"><IMGSRC="gifs/smnavbar.gif"SRC="gifs/smnavbar.gif"USEMAP="#map"BORDER="0"ALT="The UNIX CD Bookshelf Navigation"><MAPNAME="map"><AREASHAPE="RECT"COORDS="0,0,73,21"HREF="../index.htm"ALT="The UNIX CD Bookshelf"><AREASHAPE="RECT"COORDS="74,0,163,21"HREF="index.htm"ALT="UNIX Power Tools"><AREASHAPE="RECT"COORDS="164,0,257,21"HREF="../unixnut/index.htm"ALT="UNIX in a Nutshell"><AREASHAPE="RECT"COORDS="258,0,321,21"HREF="../vi/index.htm"ALT="Learning the vi Editor"><AREASHAPE="RECT"COORDS="322,0,378,21"HREF="../sedawk/index.htm"ALT="sed & awk"><AREASHAPE="RECT"COORDS="379,0,438,21"HREF="../ksh/index.htm"ALT="Learning the Korn Shell"><AREASHAPE="RECT"COORDS="439,0,514,21"HREF="../lrnunix/index.htm"ALT="Learning the UNIX Operating System"></MAP></DIV></BODY></HTML>⌨️ 快捷键说明
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