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Statements and whitespace
- Whitespace does not matter; usually either one or no spaces are
required to separate syntactic elements (enough to make them
unambiguous). Tabs and multiple spaces count as a single whitespace.
In most cases, new lines may be started any time. Indentation
can help to keep your code neat, but is not required.
- Comments start with a pound sign, #, and go to the end
of the line.
- There are numerous reserved words for built-in functions,
variable types, etc.
- User-defined functions are allowed, and may be prototyped.
- Additional functionality is gained at interpret/run time
through use or require statements, which operate
similarly to #include statements or run-time libraries
in languages like C and Java.
Variables and Operators
Variables take a symbol telling what sort of variable they are:
- $ for scalar variables (may be text or numeric)
- @ for arrays (use $ to refer to one element)
- % for associative arrays, aka hashes
Operators are typical, although the lack of variable typing
can yield some unexpected results.
- Arithmetic operators are + - * / with %
for modulus
- && and || are Boolean AND and OR
- man perlop for the complete list; most are used
very consistently with other programming languages.
Functions
- There are many built-in functions. man perlfunc for
a listing (but more functions may be added through added-in modules)
- Functions may have required or optional arguments; generally,
variables passed to functions are made local to that function
(i.e., "pass by value"). But you can also pass references, and
return values.
- Perl is not a strongly typed language. When needed, the type
of a variable is infered by context (for example, adding 1 to a
variable indicates it's a number).
- The programmer may define functions. You can also
provide for overloaded functions, classes (including both
functions & data), and other object-oriented techniques.
More on this later in the course.
Flow of Control
- Perl is a fairly linear language. Processing for a Perl
program starts at the top, though function calls can take
the flow of control anywhere.
- Advanced flow of control, such as threads or forked/child
processes, are supported.
- Loops include while, for/foreach,
and until.
- if/else/elseif is available for conditional
execution.
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