Learning Perl, Second Edition

2.6. Scalar Operators and Functions

The most common operation on a scalar variable is assignment , which is the way to give a value to a variable. The Perl assignment operator is the equal sign (much like C or FORTRAN), which takes a variable name on the left side and gives it the value of the expression on the right, like so:

$a = 17;     # give $a the value of 17
$b = $a + 3; # give $b the current value of $a plus 3 (20)
$b = $b * 2; # give $b the value of $b multiplied by 2 (40)

Notice that last line uses the $b variable twice: once to get its value (on the right side of the =), and once to define where to put the computed expression (on the left side of the =). This is legal, safe, and in fact, rather common. In fact, it's so common that we'll see in a minute that we can write this using a convenient shorthand.

You may have noticed that scalar variables are always specified with the leading $. In shell programming, you use $ to get the value, but leave the $ off to assign a new value. In Java or C, you leave the $ off entirely. If you bounce back and forth a lot, you'll find yourself typing the wrong things occasionally. This is expected. (Our solution was to stop writing shell, awk, and C programs, but that may not work for you.)

A scalar assignment may be used as a value as well as an operation, as in C. In other words, $a=3 has a value, just as $a+3 has a value. The value is the value assigned, so the value of $a=3 is 3. Although this may seem odd at first glance, using an ...