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Perl Language Reference Manual
by Larry Wall and others
Paperback (6"x9"), 724 pages
ISBN 9781906966027
RRP £29.95 ($39.95)

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29.15 O

object
An instance of a class. Something that "knows" what user-defined type (class) it is, and what it can do because of what class it is. Your program can request an object to do things, but the object gets to decide whether it wants to do them or not. Some objects are more accommodating than others.
octal
A number in base 8. Only the digits 0 through 7 are allowed. Octal constants in Perl start with 0, as in 013. See also the oct ( ) function.
offset
How many things you have to skip over when moving from the beginning of a string or array to a specific position within it. Thus, the minimum offset is zero, not one, because you don't skip anything to get to the first item.
one-liner
An entire computer program crammed into one line of text.
open source software
Programs for which the source code is freely available and freely redistributable, with no commercial strings attached. For a more detailed definition, see http://www.opensource.org/osd.html.
operand
An expression that yields a value that an operator operates on. See also precedence.
operating system
A special program that runs on the bare machine and hides the gory details of managing processes and devices. Usually used in a looser sense to indicate a particular culture of programming. The loose sense can be used at varying levels of specificity. At one extreme, you might say that all versions of Unix and Unix-lookalikes are the same operating system (upsetting many people, especially lawyers and other advocates). At the other extreme, you could say this particular version of this particular vendor's operating system is different from any other version of this or any other vendor's operating system. Perl is much more portable across operating systems than many other languages. See also architecture and platform.
operator
A gizmo that transforms some number of input values to some number of output values, often built into a language with a special syntax or symbol. A given operator may have specific expectations about what types of data you give as its arguments (operands) and what type of data you want back from it.
operator overloading
A kind of overloading that you can do on built-in operators to make them work on objects as if the objects were ordinary scalar values, but with the actual semantics supplied by the object class. This is set up with the "Package for overloading Perl operations" (overload) in the Perl Library Reference Manual (Volume 1) pragma.
options
See either switches or regular expression modifier.
overloading
Giving additional meanings to a symbol or construct. Actually, all languages do overloading to one extent or another, since people are good at figuring out things from context.
overriding
Hiding or invalidating some other definition of the same name. (Not to be confused with overloading, which adds definitions that must be disambiguated some other way.) To confuse the issue further, we use the word with two overloaded definitions: to describe how you can define your own subroutine to hide a built-in function of the same name (see 8.10) and to describe how you can define a replacement method in a derived class to hide a base class's method of the same name (see 16).
owner
The one user (apart from the superuser) who has absolute control over a file. A file may also have a group of users who may exercise joint ownership if the real owner permits it. See permission bits.
ISBN 9781906966027Perl Language Reference ManualSee the print edition