If you want to test the equality of numbers rather than strings, use the == operator.

        % perl -e ‘ if (6 == 6)   { print “true\n”; } ’
RESULT: true

        % perl -e ‘ if (6 == 5.2) { print “true\n”; } ’

ne is the opposite of eq, and!= is the opposite of ==.

        % perl -e ‘ if (“yes” ne “no”)   { print “true\n”; } ’
RESULT: true

        % perl -e ‘ if (6 != 5.2)        { print “true\n”; } ’
RESULT: true

        % perl -e ‘ $x = 8; if ($x == 8) { print “true\n”; } ’
RESULT: true

One common error (possibly the most common) among both novice and seasoned Perl programmers is using == when = is called for and vice versa. Don’t do it! Remember:

---

== vs =
== tests two numeric values; = assigns a value to a variable.

---

---

== vs eq>
== tests numbers; eq tests strings.

---

You can also compare one quantity to another. The arithmetic comparators, shown in Table 1-2, should all be familiar.

There are analogous string operators, as shown in Table 1-3.

Question: Is Hello less than or greater than hello? Or are they equal? The answer might surprise you: Hello comes before hello because the string comparators don’t use dictionary order. They use ASCII order, in which uppercase letters precede lowercase letters. (There’s a table of ASCII characters in Appendix B.)

Backslashed Characters

You’ve learned that double quotes interpolate scalars and that scalars can be identified by their dollar sign. Sometimes you’ll just want to print a plain dollar sign, using a backslash to prevent Perl from trying to interpolate variables.

print “That’ll be \$8.50, please.\n”;

See that backslash in front of the dollar sign? It’s there to keep Perl from thinking that $8 is a variable. If Perl sees “$8.50”, it interpolates $8, which is undefined, yielding

That’ll be .50, please.

Because you want to print the dollar sign, you need to let Perl know by backslashing it. There’s a simple rule about when to backslash characters inside double-quoted strings: Backslash weird characters (@, $, etc.) to get their literal meanings and backslash normal characters (n, r, t, etc.) to get their weird meanings (linefeed, carriage return, and tab, respectively).

if...else Statements

Now let’s make the if statement a bit more complex by adding an else clause, as shown in Listing 1-9.

Listing 1-9 tickets2: An if...else statement

#!/usr/bin/perl -w
print ‘Would you like to see the 11:00am showing of Cape Fear? ’;
$answer = <>;
chomp $answer;
if ($answer eq ‘yes’) {
       print “That’ll be \$8.50, please.\n”;
} else {
       print “Okay- but you’re missing a great movie. Have a nice day!\n”;
}

The if statement in tickets2 contains an else clause. As before, if ($answer eq ‘yes’), the program asks for money. But if that condition isn’t satisfied, the other print() statement executes. The statements following an else clause must be enclosed within curly braces, just like the statements following if.

% tickets2
Would you like to see the 11:00am showing of Cape Fear? no
Okay- but you’re missing a great movie.  Have a nice day!

tickets2 assumes that the user typed no if he or she didn’t type yes. What if you want your program to complain if the user said neither yes nor no? In other words

•  if (the user types yes) { ask for money }

•  otherwise if (the user types no) { say okay }

•  otherwise { say huh? }

Then you need an if...elsif...else statement, shown in Listing 1-10.

Listing 1-10 tickets3: An if...elsif...else statement

#!/usr/bin/perl
print ‘Would you like to see the 11:00am showing of Cape Fear? ’;
$answer = <>;
chomp $answer;
if  ($answer eq ‘yes’) {               # If ‘yes’ was typed...
    print “That’ll be \$8.50, please.\n”;
} elsif ($answer eq ‘no’) {            # Otherwise, if ‘no’ was typed...
    print “Okay- but you’re missing a great movie.  Have a nice day!\n”;
} else {                               # Otherwise...
    print “I’m sorry, I didn’t understand that.\n”;
}

You can have as many elsifs as you want. tickets3 just needs one because there are three possible outcomes (yes, no, and everything else), and two of those are caught by the if clause and the else clause.

        % tickets3
RESULT: Would you like to see the 11:00am showing of Cape Fear? maybe
        I’m sorry, I didn’t understand that.