File: arithexp.html

package info (click to toggle)
abs-guide 10-3
links: PTS, VCS
area: main
in suites: buster
size: 6,960 kB
sloc: sh: 14,129; makefile: 81
file content (340 lines) | stat: -rw-r--r-- 5,553 bytes
parent folder | download | duplicates (4)
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML
><HEAD
><TITLE
>Arithmetic Expansion</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
"><LINK
REL="HOME"
TITLE="Advanced Bash-Scripting Guide"
HREF="index.html"><LINK
REL="UP"
TITLE="Beyond the Basics"
HREF="part3.html"><LINK
REL="PREVIOUS"
TITLE="Command Substitution"
HREF="commandsub.html"><LINK
REL="NEXT"
TITLE="Recess Time"
HREF="recess-time.html"><META
HTTP-EQUIV="Content-Style-Type"
CONTENT="text/css"><LINK
REL="stylesheet"
HREF="common/kde-common.css"
TYPE="text/css"><META
HTTP-EQUIV="Content-Type"
CONTENT="text/html; charset=iso-8859-1"><META
HTTP-EQUIV="Content-Language"
CONTENT="en"><LINK
REL="stylesheet"
HREF="common/kde-localised.css"
TYPE="text/css"
TITLE="KDE-English"><LINK
REL="stylesheet"
HREF="common/kde-default.css"
TYPE="text/css"
TITLE="KDE-Default"></HEAD
><BODY
CLASS="CHAPTER"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#AA0000"
VLINK="#AA0055"
ALINK="#AA0000"
STYLE="font-family: sans-serif;"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>Advanced Bash-Scripting Guide: An in-depth exploration of the art of shell scripting</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="commandsub.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
></TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="recess-time.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="CHAPTER"
><H1
><A
NAME="ARITHEXP"
></A
>Chapter 13. Arithmetic Expansion</H1
><P
><A
NAME="ARITHEXPREF"
></A
>Arithmetic expansion provides a
	powerful tool for performing (integer) arithmetic
	operations in scripts. Translating a string into a
	numerical expression is relatively straightforward using
	<I
CLASS="FIRSTTERM"
>backticks</I
>, <I
CLASS="FIRSTTERM"
>double
	parentheses</I
>, or <I
CLASS="FIRSTTERM"
>let</I
>.</P
><DIV
CLASS="VARIABLELIST"
><P
><B
><A
NAME="ARITHEXPVAR1"
></A
>Variations</B
></P
><DL
><DT
>Arithmetic expansion with <A
HREF="commandsub.html#BACKQUOTESREF"
>backticks</A
> (often used in
	  conjunction with <A
HREF="moreadv.html#EXPRREF"
>expr</A
>)</DT
><DD
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;z=`expr $z + 3`          # The 'expr' command performs the expansion.</PRE
></TD
></TR
></TABLE
></P
></DD
><DT
>Arithmetic expansion with <A
HREF="dblparens.html"
>double
	  parentheses</A
>, and using <A
HREF="internal.html#LETREF"
>let</A
></DT
><DD
><P
>The use of <I
CLASS="FIRSTTERM"
>backticks</I
>
	      (<I
CLASS="FIRSTTERM"
>backquotes</I
>) in arithmetic
	      expansion has been superseded by <I
CLASS="FIRSTTERM"
>double
	      parentheses</I
> --
	      <TT
CLASS="USERINPUT"
><B
>((...))</B
></TT
> and
	      <TT
CLASS="USERINPUT"
><B
>$((...))</B
></TT
> -- and also by the very
	      convenient <A
HREF="internal.html#LETREF"
>let</A
> construction.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;z=$(($z+3))
   2&nbsp;z=$((z+3))                                  #  Also correct.
   3&nbsp;                                            #  Within double parentheses,
   4&nbsp;                                            #+ parameter dereferencing
   5&nbsp;                                            #+ is optional.
   6&nbsp;
   7&nbsp;# $((EXPRESSION)) is arithmetic expansion.  #  Not to be confused with
   8&nbsp;                                            #+ command substitution.
   9&nbsp;
  10&nbsp;
  11&nbsp;
  12&nbsp;# You may also use operations within double parentheses without assignment.
  13&nbsp;
  14&nbsp;  n=0
  15&nbsp;  echo "n = $n"                             # n = 0
  16&nbsp;
  17&nbsp;  (( n += 1 ))                              # Increment.
  18&nbsp;# (( $n += 1 )) is incorrect!
  19&nbsp;  echo "n = $n"                             # n = 1
  20&nbsp;
  21&nbsp;
  22&nbsp;let z=z+3
  23&nbsp;let "z += 3"  #  Quotes permit the use of spaces in variable assignment.
  24&nbsp;              #  The 'let' operator actually performs arithmetic evaluation,
  25&nbsp;              #+ rather than expansion.</PRE
></TD
></TR
></TABLE
>
	    </P
><P
>Examples of arithmetic expansion in scripts:
       <OL
TYPE="1"
><LI
><P
><A
HREF="moreadv.html#EX45"
>Example 16-9</A
></P
></LI
><LI
><P
><A
HREF="loops.html#EX25"
>Example 11-15</A
></P
></LI
><LI
><P
><A
HREF="arrays.html#EX66"
>Example 27-1</A
></P
></LI
><LI
><P
><A
HREF="arrays.html#BUBBLE"
>Example 27-11</A
></P
></LI
><LI
><P
><A
HREF="contributed-scripts.html#TREE"
>Example A-16</A
></P
></LI
></OL
>
     </P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="commandsub.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="recess-time.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Command Substitution</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="part3.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Recess Time</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>