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>Advanced Bash-Scripting Guide: An in-depth exploration of the art of shell scripting</TH
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>4.2. Variable Assignment</H1
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><DT
><A
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><SPAN
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>=</SPAN
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><DD
><P
>the assignment operator (<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>no space before
	    and after</I
></SPAN
>)</P
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>Do not confuse this with <A
HREF="comparison-ops.html#EQUALSIGNREF"
>=</A
> and
	      <A
HREF="comparison-ops.html#EQUALREF"
>-eq</A
>, which
	      <A
HREF="tests.html#IFTHEN"
>test</A
>,
	      rather than assign!</P
><P
>Note that <SPAN
CLASS="TOKEN"
>=</SPAN
> can be either
	      an <I
CLASS="FIRSTTERM"
>assignment</I
> or a
	      <I
CLASS="FIRSTTERM"
>test</I
> operator, depending on
	      context.</P
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>Example 4-2. Plain Variable Assignment</B
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>   1&nbsp;#!/bin/bash
   2&nbsp;# Naked variables
   3&nbsp;
   4&nbsp;echo
   5&nbsp;
   6&nbsp;# When is a variable "naked", i.e., lacking the '$' in front?
   7&nbsp;# When it is being assigned, rather than referenced.
   8&nbsp;
   9&nbsp;# Assignment
  10&nbsp;a=879
  11&nbsp;echo "The value of \"a\" is $a."
  12&nbsp;
  13&nbsp;# Assignment using 'let'
  14&nbsp;let a=16+5
  15&nbsp;echo "The value of \"a\" is now $a."
  16&nbsp;
  17&nbsp;echo
  18&nbsp;
  19&nbsp;# In a 'for' loop (really, a type of disguised assignment):
  20&nbsp;echo -n "Values of \"a\" in the loop are: "
  21&nbsp;for a in 7 8 9 11
  22&nbsp;do
  23&nbsp;  echo -n "$a "
  24&nbsp;done
  25&nbsp;
  26&nbsp;echo
  27&nbsp;echo
  28&nbsp;
  29&nbsp;# In a 'read' statement (also a type of assignment):
  30&nbsp;echo -n "Enter \"a\" "
  31&nbsp;read a
  32&nbsp;echo "The value of \"a\" is now $a."
  33&nbsp;
  34&nbsp;echo
  35&nbsp;
  36&nbsp;exit 0</PRE
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><P
><B
>Example 4-3. Variable Assignment, plain and fancy</B
></P
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>   1&nbsp;#!/bin/bash
   2&nbsp;
   3&nbsp;a=23              # Simple case
   4&nbsp;echo $a
   5&nbsp;b=$a
   6&nbsp;echo $b
   7&nbsp;
   8&nbsp;# Now, getting a little bit fancier (command substitution).
   9&nbsp;
  10&nbsp;a=`echo Hello!`   # Assigns result of 'echo' command to 'a' ...
  11&nbsp;echo $a
  12&nbsp;#  Note that including an exclamation mark (!) within a
  13&nbsp;#+ command substitution construct will not work from the command-line,
  14&nbsp;#+ since this triggers the Bash "history mechanism."
  15&nbsp;#  Inside a script, however, the history functions are disabled by default.
  16&nbsp;
  17&nbsp;a=`ls -l`         # Assigns result of 'ls -l' command to 'a'
  18&nbsp;echo $a           # Unquoted, however, it removes tabs and newlines.
  19&nbsp;echo
  20&nbsp;echo "$a"         # The quoted variable preserves whitespace.
  21&nbsp;                  # (See the chapter on "Quoting.")
  22&nbsp;
  23&nbsp;exit 0</PRE
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><P
>Variable assignment using the <I
CLASS="FIRSTTERM"
>$(...)</I
>
	      mechanism (a newer method than <A
HREF="commandsub.html#BACKQUOTESREF"
>backquotes</A
>). This is
	      likewise a form of <A
HREF="commandsub.html#COMMANDSUBREF"
>command
	      substitution</A
>.</P
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>   1&nbsp;# From /etc/rc.d/rc.local
   2&nbsp;R=$(cat /etc/redhat-release)
   3&nbsp;arch=$(uname -m)</PRE
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