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>Advanced Bash-Scripting Guide: An in-depth exploration of the art of shell scripting</TH
></TR
><TR
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><A
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><TD
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>Chapter 36. Miscellany</TD
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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="PORTABILITYISSUES"
></A
>36.9. Portability Issues</H1
><TABLE
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><TR
><TD
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>&nbsp;</TD
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ALIGN="LEFT"
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><I
><P
><I
>It is easier to port a shell than a shell script.</I
></P
><P
><I
>--Larry Wall</I
></P
></I
></TD
></TR
></TABLE
><P
>This book deals specifically with Bash scripting on
	  a GNU/Linux system. All the same, users of <B
CLASS="COMMAND"
>sh</B
>
	  and <B
CLASS="COMMAND"
>ksh</B
> will find much of value here.</P
><P
><A
NAME="POSIX3REF"
></A
>As it happens, many of the various
	  shells and scripting languages seem to be converging toward the
	  <A
HREF="sha-bang.html#POSIX2REF"
>POSIX</A
> 1003.2 standard. Invoking
	  Bash with the <TT
CLASS="OPTION"
>--posix</TT
> option or inserting
	  a <B
CLASS="COMMAND"
>set -o posix</B
> at the head of a script
	  causes Bash to conform very closely to this standard. Another
	  alternative is to use a <I
CLASS="FIRSTTERM"
>#!/bin/sh</I
> <A
HREF="sha-bang.html#SHABANGREF"
>sha-bang header</A
> in the script,
	  rather than <I
CLASS="FIRSTTERM"
>#!/bin/bash</I
>.

	    <A
NAME="AEN20799"
HREF="#FTN.AEN20799"
>[1]</A
>

	  Note that <TT
CLASS="FILENAME"
>/bin/sh</TT
> is a <A
HREF="external.html#LINKREF"
>link</A
> to <TT
CLASS="FILENAME"
>/bin/bash</TT
>
	  in Linux and certain other flavors of UNIX, and a script invoked
	  this way disables extended Bash functionality.</P
><P
>Most Bash scripts will run as-is under
	  <B
CLASS="COMMAND"
>ksh</B
>, and vice-versa, since Chet Ramey has
	  been busily porting <B
CLASS="COMMAND"
>ksh</B
> features to the
	  latest versions of Bash.</P
><P
>On a commercial UNIX machine, scripts using GNU-specific
	  features of standard commands may not work. This has become less
	  of a problem in the last few years, as the GNU utilities have
	  pretty much displaced their proprietary
	  counterparts even on <SPAN
CLASS="QUOTE"
>"big-iron"</SPAN
> UNIX.
	  <A
HREF="http://linux.oreillynet.com/pub/a/linux/2002/02/28/caldera.html"
TARGET="_top"
>Caldera's
	  release of the source</A
> to many of the original UNIX
	  utilities has accelerated the trend.</P
><P
><A
NAME="BASHCOMPAT"
></A
></P
><P
>Bash has certain features that the traditional <A
HREF="why-shell.html#BASHDEF"
>Bourne shell</A
> lacks. Among these are:

	<UL
><LI
><P
>Certain extended <A
HREF="options.html#INVOCATIONOPTIONSREF"
>invocation options</A
></P
></LI
><LI
><P
><A
HREF="commandsub.html#COMMANDSUBREF"
>Command substitution</A
> using
	  <B
CLASS="COMMAND"
>$(    )</B
> notation</P
></LI
><LI
><P
><A
HREF="bashver3.html#BRACEEXPREF3"
>Brace expansion</A
></P
></LI
><LI
><P
>Certain <A
HREF="arrays.html#ARRAYREF"
>array</A
> operations,
          and <A
HREF="bashver4.html#ASSOCARR"
>associative arrays</A
></P
></LI
><LI
><P
>The <A
HREF="tests.html#DBLBRACKETS"
>double brackets</A
>
	  extended test construct</P
></LI
><LI
><P
>The <A
HREF="dblparens.html#DBLPARENSREF"
>double-parentheses</A
>
	  arithmetic-evaluation construct</P
></LI
><LI
><P
>Certain <A
HREF="manipulatingvars.html#STRINGMANIP"
>string manipulation</A
>
	  operations</P
></LI
><LI
><P
><A
HREF="process-sub.html#PROCESSSUBREF"
>Process substitution</A
></P
></LI
><LI
><P
>A Regular Expression <A
HREF="bashver3.html#REGEXMATCHREF"
>matching
	  operator</A
></P
></LI
><LI
><P
>Bash-specific <A
HREF="internal.html#BUILTINREF"
>builtins</A
></P
></LI
><LI
><P
><A
HREF="bashver4.html#COPROCREF"
>Coprocesses</A
></P
></LI
></UL
>
	</P
><P
>See the <A
HREF="ftp://ftp.cwru.edu/pub/bash/FAQ"
TARGET="_top"
>Bash
	   F.A.Q.</A
> for a complete listing.</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN20853"
></A
>36.9.1. A Test Suite</H2
><P
><A
NAME="TESTSUITE0"
></A
>Let us illustrate some of the
	   incompatibilities between Bash and the classic
	   Bourne shell. Download and install the <A
HREF="http://freshmeat.net/projects/bournesh"
TARGET="_top"
><SPAN
CLASS="QUOTE"
>"Heirloom
	   Bourne Shell"</SPAN
></A
> and run the following
	   script, first using Bash, then the classic
	   <I
CLASS="FIRSTTERM"
>sh</I
>.</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="TESTSUITE"
></A
><P
><B
>Example 36-23. Test Suite</B
></P
><TABLE
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><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# test-suite.sh
   3&nbsp;# A partial Bash compatibility test suite.
   4&nbsp;# Run this on your version of Bash, or some other shell.
   5&nbsp;
   6&nbsp;default_option=FAIL         # Tests below will fail unless . . .
   7&nbsp;
   8&nbsp;echo
   9&nbsp;echo -n "Testing "
  10&nbsp;sleep 1; echo -n ". "
  11&nbsp;sleep 1; echo -n ". "
  12&nbsp;sleep 1; echo ". "
  13&nbsp;echo
  14&nbsp;
  15&nbsp;# Double brackets
  16&nbsp;String="Double brackets supported?"
  17&nbsp;echo -n "Double brackets test: "
  18&nbsp;if [[ "$String" = "Double brackets supported?" ]]
  19&nbsp;then
  20&nbsp;  echo "PASS"
  21&nbsp;else
  22&nbsp;  echo "FAIL"
  23&nbsp;fi
  24&nbsp;
  25&nbsp;
  26&nbsp;# Double brackets and regex matching
  27&nbsp;String="Regex matching supported?"
  28&nbsp;echo -n "Regex matching: "
  29&nbsp;if [[ "$String" =~ R.....matching* ]]
  30&nbsp;then
  31&nbsp;  echo "PASS"
  32&nbsp;else
  33&nbsp;  echo "FAIL"
  34&nbsp;fi
  35&nbsp;
  36&nbsp;
  37&nbsp;# Arrays
  38&nbsp;test_arr=$default_option     # FAIL
  39&nbsp;Array=( If supports arrays will print PASS )
  40&nbsp;test_arr=${Array[5]}
  41&nbsp;echo "Array test: $test_arr"
  42&nbsp;
  43&nbsp;
  44&nbsp;# Command Substitution
  45&nbsp;csub_test ()
  46&nbsp;{
  47&nbsp;  echo "PASS"
  48&nbsp;}
  49&nbsp;
  50&nbsp;test_csub=$default_option    # FAIL
  51&nbsp;test_csub=$(csub_test)
  52&nbsp;echo "Command substitution test: $test_csub"
  53&nbsp;
  54&nbsp;echo
  55&nbsp;
  56&nbsp;#  Completing this script is an exercise for the reader.
  57&nbsp;#  Add to the above similar tests for double parentheses,
  58&nbsp;#+ brace expansion, process substitution, etc.
  59&nbsp;
  60&nbsp;exit $?</PRE
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><H3
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>Notes</H3
><TABLE
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><TR
><TD
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><A
NAME="FTN.AEN20799"
HREF="portabilityissues.html#AEN20799"
>[1]</A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>Or, better yet, <A
HREF="system.html#ENVV2REF"
>#!/bin/env sh</A
>.</P
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