What makes you think that we have both functions and subroutines in Perl? Actually we only have subroutines.

Generally in computer science a function is a special type of subroutine that returns a values (as opposed to being called just for its side-effects). But in Perl (as the cookbook says) we don't make that distinction.

As an aside, could you please refrain from posting links to copyright-infringing web sites. O'Reilly's authors worked hard to produce those books - it would be nice if they were compensated for their effort.

Some programming languages, like Pascal and FORTRAN, distinguish between functions, which return values, and subroutines or procedures, which do not. Other languages, like C and LISP, do not make this distinction, and treat those terms as synonymous. The name method is commonly used in connection with object-oriented programming, specifically for subroutines that are part of objects.

function and subroutine are subprograms used in fortran.

function subprograms are used to compute a single value,while subroutine subprogram are used to compute several values or to perform task.

main difference between a subroutine and a function as follows:

1. No value is associated with the name of a subroutine,while the name of a function subprogram must have a value, numerical or logical.
2. A subroutine may be invoked only by a special calling statement-the call statement. The name of a function subprogram may be used in the same way as library functions,,i.e.,in arithmetic statements,etc.
3. A FUNCTION subprogram must have at least one argument, while a subroutine need not have any.
4. Since a function subprogram computes atleast one value, it must contain a return statement. A SUBROUTINE subprogram need not contain return statement.

Traditionally, outside of Perl,

• Functions:

  returned values that were used as a part of the calling expression.

  Preferably they do not have side-effects.

• procedures:

  Returned only status. True/false, an error code or an exception.

  Usually side-effectful.

• subroutine:

  A generic term covering both and more.

I'm not sure if there is any language that actually enforced these rules. Didn't Pascal complain if you tried to return a value from a procedure?

The way I always explain it: CODE objects are declared as subroutines, but used either as functions or methods. Or even both, if you want to confuse people (CGI.pm does, apparantly):

sub foo { print @_ }

foo "Hello "; # function - prints "Hello "

main->foo("!"); # method - prints "main!"
[download]

You cannot call a subroutine except as a function or a method.

Nor can you write a function or method, except as a subroutine.

The two words mean the same thing. They're synonyms.

Nitpick--ITYM "synonym".

http://en.wikipedia.org/wiki/Homonym
http://en.wikipedia.org/wiki/Synonym

A function is not necessarily a computing term -- in the English language it could mean anything from something your body does to a social event. A subroutine, however, is pretty much limited to a computing term, although i'm sure someone has used it outside of that scope. (UPDATE: touché, ysth!) In Perl, i tend to refer to the built-in functions such as print and sort as functions, but i refer to my own functions as subroutines. Of interest is perldoc -f, which is used to pull up documentation for Perl's built-in subroutines [sic]. ;) Notice it is -f and not -s.

As diotalevi said, they are homonyms in terms of computing.

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

My day has gone no better than usual, but at least it wasn't subroutine.

Then why we are having subroutine,function in perl.