Is & a command?

Hi Folks,

In UNIX there is a command named “test” which is used like this:

             test expression

Upon encountering that, a UNIX-aware application (e.g., a UNIX shell) will call the test command to evaluate expression.

Interestingly, these two forms are equivalent:

             test expression

             [ expression ]

The book [1] that I am reading says this about the second form:

The [ is actually the name of the command
             (who said anything about command names
             having to be alphanumeric characters?). It
             still initiates execution of the same test
             command, only in this format, test expects
             to see a closing ] at the end of the expression.

Okay, now to XML ….

An XML document may contain this:

             <

Upon encountering that, an XML-aware application (e.g., an XML parser) will call a routine to convert the entity. One might say this:

The & is actually the name of the command.
             It initiates execution of the & command and
             expects to see a closing ; at the end.

So, …………….

Is & a command?

Likewise, ……………..

Is < a command?

Is " a command?

If the answers are no, then what are they? What is the difference between a command and whatever those things are?

/Roger

[1] UNIX Shell Programming by Kochan and Wood, p. 155.