Programming Perl, 4th Edition

What Is a Reference?

In our example, $vitals[0] has the value “john”. That is, it contains a string that happens to be the name of another (global) variable. We say that the first variable refers to the second, and this sort of reference is called a symbolic reference, since Perl has to look up @john in a symbol table to find it. (You might think of symbolic references as analogous to symbolic links in the filesystem.) We’ll talk about symbolic references later in this chapter.

The other kind of reference is a hard reference, and this is what most Perl programmers use to accomplish their indirections (if not their indiscretions). We call them hard references not because they’re difficult, but because they’re real and solid. If you like, think of hard references as real references and symbolic references as fake references. It’s like the difference between true friendship and mere name-dropping. When we don’t specify which type of reference we mean, it’s a hard reference. Figure 8-1 depicts a variable named $bar referring to the contents of a scalar named $foo, which has the value “bot”.

Figure 8-1. A hard reference and a symbolic reference

Unlike a symbolic reference, a real reference refers not to the name of another variable (which is just a container for a value) but to an actual value itself, some internal glob of data. There’s no good word for that thing, but when we have to, we’ll ...