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>Advanced Bash-Scripting Guide: An in-depth exploration of the art of shell scripting</TH
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><TR
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><A
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><TD
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>Chapter 37. Bash, versions 2, 3, and 4</TD
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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="BASHVER3"
></A
>37.2. Bash, version 3</H1
><P
><A
NAME="BASH3REF"
></A
></P
><P
>On July 27, 2004, Chet Ramey released version 3 of Bash.
        This update fixed quite a number of bugs and added new
        features.</P
><P
>Some of the more important added features:

      <UL
><LI
><P
><A
NAME="BRACEEXPREF3"
></A
></P
><P
>A new, more generalized <B
CLASS="COMMAND"
>{a..z}</B
> <A
HREF="special-chars.html#BRACEEXPREF"
>brace expansion</A
> operator.</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;
   3&nbsp;for i in {1..10}
   4&nbsp;#  Simpler and more straightforward than
   5&nbsp;#+ for i in $(seq 10)
   6&nbsp;do
   7&nbsp;  echo -n "$i "
   8&nbsp;done
   9&nbsp;
  10&nbsp;echo
  11&nbsp;
  12&nbsp;# 1 2 3 4 5 6 7 8 9 10
  13&nbsp;
  14&nbsp;
  15&nbsp;
  16&nbsp;# Or just . . .
  17&nbsp;
  18&nbsp;echo {a..z}    #  a b c d e f g h i j k l m n o p q r s t u v w x y z
  19&nbsp;echo {e..m}    #  e f g h i j k l m
  20&nbsp;echo {z..a}    #  z y x w v u t s r q p o n m l k j i h g f e d c b a
  21&nbsp;               #  Works backwards, too.
  22&nbsp;echo {25..30}  #  25 26 27 28 29 30
  23&nbsp;echo {3..-2}   #  3 2 1 0 -1 -2
  24&nbsp;echo {X..d}    #  X Y Z [  ] ^ _ ` a b c d
  25&nbsp;               #  Shows (some of) the ASCII characters between Z and a,
  26&nbsp;               #+ but don't rely on this type of behavior because . . .
  27&nbsp;echo {]..a}    #  {]..a}
  28&nbsp;               #  Why?
  29&nbsp;
  30&nbsp;
  31&nbsp;# You can tack on prefixes and suffixes.
  32&nbsp;echo "Number #"{1..4}, "..."
  33&nbsp;     # Number #1, Number #2, Number #3, Number #4, ...
  34&nbsp;
  35&nbsp;
  36&nbsp;# You can concatenate brace-expansion sets.
  37&nbsp;echo {1..3}{x..z}" +" "..."
  38&nbsp;     # 1x + 1y + 1z + 2x + 2y + 2z + 3x + 3y + 3z + ...
  39&nbsp;     # Generates an algebraic expression.
  40&nbsp;     # This could be used to find permutations.
  41&nbsp;
  42&nbsp;# You can nest brace-expansion sets.
  43&nbsp;echo {{a..c},{1..3}}
  44&nbsp;     # a b c 1 2 3
  45&nbsp;     # The "comma operator" splices together strings.
  46&nbsp;
  47&nbsp;# ########## ######### ############ ########### ######### ###############
  48&nbsp;# Unfortunately, brace expansion does not lend itself to parameterization.
  49&nbsp;var1=1
  50&nbsp;var2=5
  51&nbsp;echo {$var1..$var2}   # {1..5}
  52&nbsp;
  53&nbsp;
  54&nbsp;# Yet, as Emiliano G. points out, using "eval" overcomes this limitation.
  55&nbsp;
  56&nbsp;start=0
  57&nbsp;end=10
  58&nbsp;for index in $(eval echo {$start..$end})
  59&nbsp;do
  60&nbsp;  echo -n "$index "   # 0 1 2 3 4 5 6 7 8 9 10 
  61&nbsp;done
  62&nbsp;
  63&nbsp;echo</PRE
></TD
></TR
></TABLE
></P
></LI
><LI
><P
>The <B
CLASS="COMMAND"
>${!array[@]}</B
> operator, which
	    expands to all the indices of a given <A
HREF="arrays.html#ARRAYREF"
>array</A
>.</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;
   3&nbsp;Array=(element-zero element-one element-two element-three)
   4&nbsp;
   5&nbsp;echo ${Array[0]}   # element-zero
   6&nbsp;                   # First element of array.
   7&nbsp;
   8&nbsp;echo ${!Array[@]}  # 0 1 2 3
   9&nbsp;                   # All the indices of Array.
  10&nbsp;
  11&nbsp;for i in ${!Array[@]}
  12&nbsp;do
  13&nbsp;  echo ${Array[i]} # element-zero
  14&nbsp;                   # element-one
  15&nbsp;                   # element-two
  16&nbsp;                   # element-three
  17&nbsp;                   #
  18&nbsp;                   # All the elements in Array.
  19&nbsp;done</PRE
></TD
></TR
></TABLE
></P
></LI
><LI
><P
><A
NAME="REGEXMATCHREF"
></A
></P
><P
>The <B
CLASS="COMMAND"
>=~</B
> <A
HREF="regexp.html#REGEXREF"
>Regular
	    Expression</A
> matching operator within a <A
HREF="tests.html#DBLBRACKETS"
>double brackets</A
> test expression.
	    (Perl has a similar operator.)</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;
   3&nbsp;variable="This is a fine mess."
   4&nbsp;
   5&nbsp;echo "$variable"
   6&nbsp;
   7&nbsp;# Regex matching with =~ operator within [[ double brackets ]].
   8&nbsp;if [[ "$variable" =~ T.........fin*es* ]]
   9&nbsp;# NOTE: As of version 3.2 of Bash, expression to match no longer quoted.
  10&nbsp;then
  11&nbsp;  echo "match found"
  12&nbsp;      # match found
  13&nbsp;fi</PRE
></TD
></TR
></TABLE
></P
><P
>Or, more usefully:</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;
   3&nbsp;input=$1
   4&nbsp;
   5&nbsp;
   6&nbsp;if [[ "$input" =~ "[0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9][0-9][0-9]" ]]
   7&nbsp;#                 ^ NOTE: Quoting not necessary, as of version 3.2 of Bash.
   8&nbsp;# NNN-NN-NNNN (where each N is a digit).
   9&nbsp;then
  10&nbsp;  echo "Social Security number."
  11&nbsp;  # Process SSN.
  12&nbsp;else
  13&nbsp;  echo "Not a Social Security number!"
  14&nbsp;  # Or, ask for corrected input.
  15&nbsp;fi</PRE
></TD
></TR
></TABLE
></P
><P
>For additional examples of using the
                <B
CLASS="COMMAND"
>=~</B
> operator, see <A
HREF="contributed-scripts.html#WHX"
>Example A-29</A
>,
                <A
HREF="here-docs.html#MAILBOXGREP"
>Example 19-14</A
>, <A
HREF="contributed-scripts.html#FINDSPLIT"
>Example A-35</A
>, and <A
HREF="contributed-scripts.html#TOHTML"
>Example A-24</A
>.</P
></LI
><LI
><P
><A
NAME="PIPEFAILREF"
></A
></P
><P
>The new <TT
CLASS="OPTION"
>set -o pipefail</TT
> option is
	    useful for debugging <A
HREF="special-chars.html#PIPEREF"
>pipes</A
>. If
	    this option is set, then the <A
HREF="exit-status.html#EXITSTATUSREF"
>exit status</A
> of a pipe
	    is the exit status of the last command in the pipe to
	    <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>fail</I
></SPAN
> (return a non-zero value), rather
	    than the actual final command in the pipe.</P
><P
>See <A
HREF="communications.html#FC4UPD"
>Example 16-43</A
>.</P
></LI
></UL
>
      </P
><DIV
CLASS="CAUTION"
><TABLE
CLASS="CAUTION"
WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/caution.png"
HSPACE="5"
ALT="Caution"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>The update to version 3 of Bash breaks a few scripts
        that worked under earlier versions. <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>Test critical legacy
	scripts to make sure they still work!</I
></SPAN
></P
><P
>As it happens, a couple of the scripts in the
        <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>Advanced Bash Scripting Guide</I
></SPAN
> had to be
        fixed up (see <A
HREF="variables2.html#TOUT"
>Example 9-4</A
>, for instance).</P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN20956"
></A
>37.2.1. Bash, version 3.1</H2
><P
>The version 3.1 update of Bash introduces a number of bugfixes
	   and a few minor changes.</P
><UL
><LI
><P
>The <SPAN
CLASS="TOKEN"
>+=</SPAN
> operator is now permitted in
	        in places where previously only the <SPAN
CLASS="TOKEN"
>=</SPAN
>
		assignment operator was recognized.</P
><P
><A
NAME="PLUSEQSTR"
></A
></P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;a=1
   2&nbsp;echo $a        # 1
   3&nbsp;
   4&nbsp;a+=5           # Won't work under versions of Bash earlier than 3.1.
   5&nbsp;echo $a        # 15
   6&nbsp;
   7&nbsp;a+=Hello
   8&nbsp;echo $a        # 15Hello</PRE
></TD
></TR
></TABLE
>
	      </P
><P
>Here, <SPAN
CLASS="TOKEN"
>+=</SPAN
> functions as a <I
CLASS="FIRSTTERM"
>string
		concatenation</I
> operator. Note that its behavior
		in this particular context is different than within a
		<A
HREF="internal.html#LETREF"
>let</A
> construct.</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;a=1
   2&nbsp;echo $a        # 1
   3&nbsp;
   4&nbsp;let a+=5       # Integer arithmetic, rather than string concatenation.
   5&nbsp;echo $a        # 6
   6&nbsp;
   7&nbsp;let a+=Hello   # Doesn't "add" anything to a.
   8&nbsp;echo $a        # 6</PRE
></TD
></TR
></TABLE
>
	      </P
><P
><A
NAME="PATHAPPEND"
></A
>Jeffrey Haemer points out
		that this concatenation operator can be quite
		useful. In this instance, we append a directory to the
		<TT
CLASS="VARNAME"
>$PATH</TT
>.</P
><P
>&#13;      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>echo $PATH</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>/usr/bin:/bin:/usr/local/bin:/usr/X11R6/bin/:/usr/games</TT
>
 
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>PATH+=:/opt/bin</B
></TT
>
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>echo $PATH</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>/usr/bin:/bin:/usr/local/bin:/usr/X11R6/bin/:/usr/games:/opt/bin</TT
>
       </PRE
></TD
></TR
></TABLE
>

	      </P
></LI
></UL
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN20987"
></A
>37.2.2. Bash, version 3.2</H2
><P
>This is pretty much a bugfix update.</P
><UL
><LI
><P
>In <A
HREF="parameter-substitution.html#PSGLOB"
><I
CLASS="FIRSTTERM"
>global</I
>
	        parameter substitutions</A
>, the pattern no longer anchors
		at the start of the string.</P
></LI
><LI
><P
>The <TT
CLASS="OPTION"
>--wordexp</TT
> option disables
	        <A
HREF="process-sub.html#PROCESSSUBREF"
>process substitution</A
>.</P
></LI
><LI
><P
>The <B
CLASS="COMMAND"
>=~</B
> <A
HREF="bashver3.html#REGEXMATCHREF"
>Regular Expression
                match operator</A
> no longer requires
                <A
HREF="quoting.html#QUOTINGREF"
>quoting</A
> of the
                <I
CLASS="FIRSTTERM"
>pattern</I
> within <A
HREF="tests.html#DBLBRACKETS"
>[[ ... ]]</A
>.</P
><DIV
CLASS="CAUTION"
><TABLE
CLASS="CAUTION"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/caution.png"
HSPACE="5"
ALT="Caution"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>In fact, quoting in this context is
		<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> advisable as it may
		cause <I
CLASS="FIRSTTERM"
>regex</I
> evaluation to fail.
		Chet Ramey states in the <A
HREF="biblio.html#BASHFAQ"
>Bash
		FAQ</A
> that quoting explicitly disables regex evaluation.
		See also the <A
HREF="https://bugs.launchpad.net/ubuntu-website/+bug/109931"
TARGET="_top"
>		Ubuntu Bug List</A
> and <A
HREF="http://en.wikinerds.org/index.php/Bash_syntax_and_semantics"
TARGET="_top"
>		Wikinerds on Bash syntax</A
>.</P
><P
>Setting <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>shopt -s compat31</I
></SPAN
>
                  in a script causes reversion to the original
                  behavior.</P
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