Question

I’m reading Beginning Perl by Simon Cozens and in Chapter 8 – Subroutines he states that “subroutines” are user functions, while print, open, split, etc. are built-in operators or functions.

What are they? Are they really built-in, language-intrinsic features (like C’s sizeof operator) or are they, actually, subroutines/functions of the main module?

If they’re subroutines, are while, for, unless, etc. also subroutines? What about the operators like +, -, eq, etc.?

Answer 1

print, open, split are not subroutines. They do not result in sub calls. They are not even present in the symbol table (in main:: or otherwise, although you can refer to them as CORE::split, etc), and one cannot get a reference to their code (although work is being done to create proxy subs for them in CORE:: for when you want to treat them as subroutines). They are operators just like +.

$ perl -MO=Concise,-exec -e'sub f {} f()'
1  <0> enter 
2  <;> nextstate(main 2 -e:1) v:{
3  <0> pushmark s
4  <#> gv[*f] s
5  <1> entersub[t3] vKS/TARG,1      <--- sub call
6  <@> leave[1 ref] vKP/REFC
-e syntax OK

$ perl -MO=Concise,-exec -e'split /;/'
1  <0> enter 
2  <;> nextstate(main 1 -e:1) v:{
3  </> pushre(/";"/) s/64
4  <#> gvsv[*_] s
5  <$> const[IV 0] s
6  <@> split[t2] vK                 <--- not a sub call
7  <@> leave[1 ref] vKP/REFC
-e syntax OK

$ perl -MO=Concise,-exec -e'$x + $y'
1  <0> enter 
2  <;> nextstate(main 1 -e:1) v:{
3  <#> gvsv[*x] s
4  <#> gvsv[*y] s
5  <2> add[t3] vK/2                 <--- Just like this
6  <@> leave[1 ref] vKP/REFC
-e syntax OK

They are known by a variety of names:

• builtin functions
• functions
• builtins
• named operators

And most are considered to be one of the following:

• list operator
• named unary operator

Subroutines are often called functions (as they are in C and C++), so “function” is an ambiguous word. This ambiguity appears to be the basis of your question.

---

As for while, for, unless, etc, they are keywords used by flow control statements

while (f()) { g() }

and statement modifiers

g() while f();