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</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Insert the next character literally, such as \$ puts $</FONT>

</TABLE><P>In line 6, the script uses the back quotes (') to execute a command and then returns the results in the $date variable. The string in between the two back quotes is what you would type at the command line, with one exception: if you use Perl 
variables in the command line for the back quotes, Perl will evaluate these variables before passing it off to the shell for execution. For example, line 6 could be rewritten as

<BR>

<PRE>

<FONT COLOR="#000080">$parm = &quot;+%D&quot;;

$date = '$date $parm';</FONT></PRE>

<P>The returned value in $date is printed out in line 7. Note that there is an extra carriage return in the text for data. To remove it, use the chop command as shown in line 8.

<BR>

<P>Then in line 9, the $date output is shown to print correctly. Note how the period (.) is used to concatenate three strings together for the output.

<BR>

<P>It's easy to construct strings in Perl with the (.) operator. Given two strings $first and $last, you can construct the string $fullname like this to get &quot;Jim Smith&quot;:

<BR>

<PRE>

<FONT COLOR="#000080">$first = &quot;Jim&quot;;

$last = &quot;Smith&quot;;

$fullname = $first . &quot; &quot; . $last;</FONT></PRE>

<P>Numbers in Perl are stored as floating point numbers; even variables used as integers are really stored as floating point numbers. There are a set of operations you can do with numbers. These operations are listed in Table 29.2.

<BR>

<P>Table 29.2 also lists Boolean operators.

<BR>

<BR>

<P ALIGN=CENTER>

<CENTER>

<FONT COLOR="#000080"><B>Table 29.2. Numeric operations with Perl.</B></FONT></CENTER>

<BR>



<TABLE  BORDERCOLOR=#000040 BORDER=1 CELLSPACING=2 WIDTH="100%" CELLPADDING=2 >

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<I>Operations</I>

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<I>Comparisons</I></FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = $x + $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Add $x to $y and assign result to $r</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = $x - $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Subtract $y from $x and assign result to $r</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = $x * $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Multiply $y and $x and assign result to $r</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = $x / $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Divide $x by $y and assign result to $r</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = $x % $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Modulo. Divide $x by $y and assign remainder to $r</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = $x ** $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Raise $x to power of $y and assign result to $r</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = $x &lt;&lt; $n

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Shift bits in $x left $n times and assign to $r</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = $x &gt;&gt; $n

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Shift bits in $x right $n times and assign to $r</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = ++$x 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Increment $x, and assign $x to $r</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = $x++ 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Assign $x to $r, then increment $x</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r += $x;

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Add $x to $r, then assign to $r</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = &#151;$x 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Decrement $x, and assign $x to $r</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = $x&#151; 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Assign $x to $r, then decrement $x</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r -= $x;

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Subtract $x from $r, then assign to $r</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r /= $x;

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Divide $r by $x, then assign to $r</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r *= $x;

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Multiply $r by $x, then assign to $r</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = $x &lt;=&gt; $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r is 1 if $x &gt; $y; 0 if $x == $y; -1 if $x &lt; $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r =~ $x 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Bind $x to $r</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = $x || $y

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = $x logical or $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = $x &amp;&amp; $y

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = $x logical and $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = ! $x 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$r = logical not $x</FONT>

</TABLE><P>You can compare values of variables to check results of operations. Table 29.3 lists the comparison operators for numbers and strings.

<BR>

<BR>

<P ALIGN=CENTER>

<CENTER>

<FONT COLOR="#000080"><B>Table 29.3. Comparison operations with Perl.</B></FONT></CENTER>

<BR>



<TABLE  BORDERCOLOR=#000040 BORDER=1 CELLSPACING=2 WIDTH="100%" CELLPADDING=2 >

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<I>Operations</I>

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

<I>Comparisons</I></FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$x == $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

True if $x is equal to $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$x != $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

True if $x is not equal to $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$x &lt; $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

True if $x is less than $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$x &lt;= $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

True if $x is less than or equal to $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$x &gt; $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

True if $x is greater than $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$x &gt;= $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

True if $x is greater than or equal to $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$x eq $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

True if string $x is equal to string $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$x ne $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

True if string $x is not equal to string $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$x lt $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

True if string $x is less than string $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$x le $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

True if string $x is less than or equal to string $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$x gt $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

True if string $x is less than string $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$x ge $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

True if string $x is less than or equal to string $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$x x $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Repeat $x, $y times</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$x . $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Return the concatenated value of $x and $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$x cmp $y 

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Return 1 if $x gt $y, 0 if $x eq $y, -1 if $x lt $y</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

$w ? $x : $y

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Return $x if $w is true, $y if $w is false</FONT>

<TR>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

 ($x..$y)

</FONT>

<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Return a list of numbers from $x to $y</FONT>

</TABLE><BR>

<A NAME="E68E231"></A>

<H3 ALIGN=CENTER>

<CENTER>

<FONT SIZE=5 COLOR="#FF0000"><B>Arrays and Associative Arrays</B></FONT></CENTER></H3>

<BR>

<P>Perl has arrays to let you group items using a single variable number. Perl offers two types of arrays: those whose items are indexed by number (arrays) and those whose items are indexed by a string (associative arrays).

<BR>

<P>An index into an array is referred to as the subscript of the array.

<BR>

<BLOCKQUOTE>

<BLOCKQUOTE>

<HR ALIGN=CENTER>

<BR>

<NOTE>An associative array is referred to as &quot;hash&quot; because of the way it's stored internally in Perl.</NOTE>

<BR>

<HR ALIGN=CENTER>

</BLOCKQUOTE></BLOCKQUOTE>

<P>Arrays are referred to with the @ symbol. Individual items in an array are derived with a $ and the subscript. For example, the first item in an array @count would be $count[0], the second item would be $count[1], and so on. See Listing 29.2 for some 
usage of arrays.

<BR>

<P>

<FONT COLOR="#000080"><B>Listing 29.2. Using arrays.</B></FONT>
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