CODEWITHSUNDEEP
perl
leesuh
leesuh

Reputation: 29

What is the difference between subroutines and scripts in Perl?

I am in the midst of learning Perl, and I have encountered a question. What, exactly is the difference between subroutines and scripts?

Upvotes: 2

Views: 436

Answers (2)

DVK
DVK

Reputation: 129433

A script is just a name for a (usually short) program usually contained in a single file. It's not really a scientific/technical term and therefore is pretty vague - people can refer to a "script" when discussing a 3-line quick program, or a 10000 lines of code program.

Some people refer to ANY Perl program as a "script" - see below for the historical reason. Some people, when they say "a Perl script" as opposed to a Perl "program", mean a relatively simple, relatively short program, frequently structured without using any subroutines/classes/other methods of code organization. Again, there's no standard definition.

As an aside, the reason why Perl programs are frequently called "scripts" is that Perl originally was used for writing scripts that perform work in Unix shell, the way shell scripting languages were used. The term "scripting language" means a language used to control an application, in this case Unix shell.

Of course, since then Perl has grown to become a full fledged programming language, but the word/term remained, sometimes used by inertia, sometimes derogatorily.

A subroutine (also known as a procedure, function, routine, method, or subprogram) is a portion of code within a larger program that performs a specific task and is relatively independent of the remaining code. It is frequently meant to contain code that performs the task which needs to be done several times in your program, or even by multiple programs.

A subroutine is NOT a Perl specific concept, though calling it "subroutine" is done in very few languages (most use the term function, method or procedure).

As a special side note, a "method" - in Perl as well as other languages - is a special type of subroutine which is associated with an object oriented class or an object of that class. The fact that it's merely a special case of a subroutine is, of course, highlighted by the fact that - despite deepest wishes by "Modern Perl" author chromatic - methods in Perl 5 are declared with "sub" keyword, same as regular subroutines.

As noted above, some people, when referring to a Perl program as a "script", imply that it does not contain subroutines (e.g. anything complicated enough to have a subroutine is no longer a "script" but a "program"). But that is not an accepted or formal definition - as stated, there is no definition of what a script is, everyone uses the term any which way they want.

Upvotes: 7

Greg Hewgill
Greg Hewgill

Reputation: 993451

A script is usually a file, which can contain statements and subroutines. A subroutine is something you find within a script.

Subroutines are described in detail in the perlsub manual page.

Upvotes: 1

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