Perl Scalars
The most basic kind of variable in Perl is the scalar variable.
Scalar variables hold both strings and numbers, and are remarkable in
that strings and numbers are completely interchangable. For example,
the statement
$priority =10;
sets the scalar variable $priority to 10, but you can also assign a string
to exactly the same variable:
$priority = ‘high’;
Perl also accepts numbers as strings, like this:
$priority = ’10’;
$default = ‘0010’;
and can still cope with arithmetic and other operations quite happily.
In general variable names consists of numbers, letters and underscores, but
they should not start with a number and the variable $_ is
special, as we’ll see later. Also, Perl is case sensitive, so
$a and $A are different.
Operations and Assignment
Perl uses all the usual C arithmetic operators:
| $a = 1 + 2; | # Add 1 and 2 and store in $a |
| $a = 3 – 4; | # Subtract 4 from 3 and store in $a |
| $a = 5 * 6; | # Multiply 5 and 6 |
| $a = 7 / 8; | # Divide 7 by 8 to give 0.875 |
| $a = 9 ** 10; | # Nine to the power of 10 |
| $a = 5 % 2; | # Remainder of 5 divided by 2 |
| ++$a; | # Increment $a and then return it |
| $a++; | # Return $a and then increment it |
| –$a; | # Decrement $a and then return it |
| $a–; | # Return $a and then decrement it |
and for strings Perl has the following among others:
| $a = $b . $c; | # Concatenate $b and $c |
| $a = $b x $c; | # $b repeated $c times |
To assign values Perl includes
| $a = $b; | # Assign $b to $a |
| $a += $b; | # Add $b to $a |
| $a -= $b; | # Subtract $b from $a |
| $a .= $b; | # Append $b onto $a |
Note that when Perl assigns a value with $a = $b it makes
a copy of $b and then assigns that to $a. Therefore the next time you change
$b it will not alter $a.
Interpolation
The following code prints apples and pears using concatenation:
$a = ‘apples’;
$b = ‘pears’;
print $a.’ and ‘.$b;
It would be nicer to include only one string in the final print statement,
but the line
print ‘$a and $b’;
prints literally $a and $b which isn’t very helpful. Instead we
can use the double quotes in place of the single quotes:
print “$a and $b”;
The double quotes force interpolation of any codes, including
interpreting variables. This is a much nicer than our original statement.
Other codes that are interpolated include special characters such as
newline and tab. The code n is a newline and
t is a tab.