Variables in Perl

Perl module P301

Variables in Perl

Exercises, examples and other material relating to training module P301. This topic is presented on public course Perl for Larger Projects

Perl variables come in seven types. You should be familiar with scalars, lists and hashes before you start this module, but you've probably still got more to learn. And how about code variables, file handles and typeglobs?

Articles and tips on this subject		updated
4608	Introspecion in Perl 6 Perl 6 provides introspection - that's the ability for its object to be able to report on methods, attributes and inheritances. And if you run Perl6 without an input file, it goes into a read - interpret - run cycle with each line you type in, rather like Python, Ruby and Tcl do. So we can experiment ...	2016-01-02
4398	Accessing variables across subroutine boundaries - Perl, Python, Java and Tcl In a perfect programming world, code is broken into named blocks (methods, functions, subroutines, classes, procedures, commands, modules, packages etc) and data is passed around between the blocks purely as parameters and return values. And variables are local to the block in which they're used. This ...	2015-01-18
3430	Sigils - the characters on the start of variable names in Perl, Ruby and Fortran A sigil (from Latin sigillum "seal") is a symbol created for a specific magical purpose. A sigil is usually made up of a complex combination of several specific symbols or geometric figures, each with a specific meaning or intent. In computer programming, a sigil is a special symbol attached to a variable ...	2011-09-10
3059	Object Orientation in an hour and other Perl Lectures I enjoy the occasional course that's different in its design and specification, and yesterday was one of those - more lectures that training, on intermediate and advanced Perl, for a group of eight delegates who were all well experienced at PHP, but Perl "dabblers" to this point. During the day, we ...	2010-12-04
2972	Some more advanced Perl examples from a recent course I ran an extra Perl for larger projects course, single company, at the tail end of last week and into the weekend (the only gap in my diary for a few weeks!) and - as is often the case on single-company courses - I wrote some new illustrative code to show specific subjects that came up in a different ...	2010-09-27
2877	Further more advanced Perl examples I've uploaded a further batch of new examples (that makes around 40 in total!) from the private Perl course that I ran from Wednesday through Saturday last week - many of them adding a new twist on to previous examples. If you read a comment below and thing "that's what I'm looking for an example of", ...	2010-07-30 (longer)
1946	Variable Types in Perl In Perl, you have "autovivification" where variables are created when they have a values set in them, without the need to declare them. Some authorities will tell you that they are also "autotyped" in that Perl knows what to store in them automatically too, and to some extent that's true ... but the ...	2010-06-23
2374	Lead characters on Perl variable names Perl variable names mostly start with a special character: $ for a scalar variable - that's a variable that can hold an integer, a float, a string, a reference, or a compiled regular expression (that last not being terribly common). @ for a list - that's an ordered collection of scalars, indexed from ...	2009-08-26 (longer)
2241	Perl references - $$var and \$var notations In Perl, if I write: $stuff = "Porridge"; then I'm setting up a variable to contain the value "Porridge". If I write: $stuffat = \$stuff; then I'm setting up a variable to contain the ADDRESS OF the variable $stuff. So if $stuff was in memory at (hex)fe80 ... then $stuffat will be assigned that value ...	2009-06-22
1581	What is an lvalue? (Perl, C) An lvalue is an expression that you can write on the left hand side of an assignment statement - in other words an expression that defines a specific memory address of a variable. The most common lvalues are simple variables or array / list / hash / dictionary members ... for example $hello = "Hello ...	2008-03-18
975	Answering ALL the delegate's Perl questions During courses, questions arise. "I'll get back to that" could make people feel that I'm brushing something off ... except that I explain, early on, that some questions require a great deal of background knowledge to be answered sensibly. And I keep a list of topics that I'll be getting back to ...	2006-12-09

Examples from our training material

danger	What variables have I used?
dele	delete, undef, defined and exists
fact	recursion in Perl
gawd	Typeglob - one each of file handle, scalar, hash and list
henry	Variable types
iiw	my, local and global variables
mkd2	Anonymous lists using [ and ]
mkpascal	Pascal's triangle; clever use of formatting
my2	scoping with "my"
myscope	Scoping of our and my variables
pers	persistent my variable
phash	data munging - unpack, splice, regular expressions etc
ref1	References
ref2	Modifying values passed in to a subroutine
ref3	handling a list of lists element by element, by row, and as a whole
scal_type	ref function - what is in a scalar
scope	variable scope illustration
sfact	Beware of variable scope in recursive code
sfact1	Use of strict to flag scoping dangers
sfact3	Using package names to supress strict warnings
splitter	select and typeglobs for file handles - alternative to array of file handles
st	Accessing Perl's symbol tables
st2	Dumping out all variables defined
tgd	typeglobs - a package deal (one of everything!)
ty	Setting up and exercising a typeglob
vartypedemo	6 variable types in Perl
vbn	Soft References

Background information

Some modules are available for download as a sample of our material or under an Open Training Notes License for free download from [here].

Topics covered in this module

Variable types.
Scalars.
Lists.
Hashes.
Code.
File Handles.
Typeglobs.
Symbol Tables.
Soft references.
undef and delete.
Variable scope.
local variables.
my variables.
Further examples using my variables.
strict.
References.
Using a reference within a subroutine.
Multidimensional lists.
Dynamic creation of structures.
Anonymous data.

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