A perl script consists of a sequence of declarations and
commands. The only things that need to be declared in perl are
report formats and subroutines. See the sections below for more
information on those declarations. All uninitialized user-created
objects are assumed to start with a null or 0 value until they are
defined by some explicit operation such as assignment. The sequence of
commands is executed just once, unlike in sed and awk
scripts, where the sequence of commands is executed for each input line.
While this means that you must explicitly loop over the lines of your
input file (or files), it also means you have much more control over
which files and which lines you look at. (Actually, I'm lying--it is
possible to do an implicit loop with either the `-n' or `-p'
switch.)
A declaration can be put anywhere a command can, but has no effect on the execution of the primary sequence of commands--declarations all take effect at compile time. Typically all the declarations are put at the beginning or the end of the script.
Perl is, for the most part, a free-form language. (The only exception to this is format declarations, for fairly obvious reasons.) Comments are indicated by the `#' character, and extend to the end of the line. If you attempt to use `/* */' C comments, it will be interpreted either as division or pattern matching, depending on the context. So don't do that.