### 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.