DESCRIPTION
The functions in this section can serve as terms in an expression.
They fall into two major categories: list operators and named unary
operators. These differ in their precedence relationship with a
following comma. (See the precedence table in perlop.) List
operators take more than one argument, while unary operators can never
take more than one argument. Thus, a comma terminates the argument of
a unary operator, but merely separates the arguments of a list
operator. A unary operator generally provides a scalar context to its
argument, while a list operator may provide either scalar and list
contexts for its arguments. If it does both, the scalar arguments will
be first, and the list argument will follow. (Note that there can only
ever be one list argument.) For instance, splice() has three scalar
arguments followed by a list.
In the syntax descriptions that follow, list operators that expect a
list (and provide list context for the elements of the list) are shown
with LIST as an argument. Such a list may consist of any combination
of scalar arguments or list values; the list values will be included
in the list as if each individual element were interpolated at that
point in the list, forming a longer single™dimensional list value.
Elements of the LIST should be separated by commas.
Any function in the list below may be used either with or without
parentheses around its arguments. (The syntax descriptions omit the
parens.) If you use the parens, the simple (but occasionally
surprising) rule is this: It LOOKS like a function, therefore it IS a
function, and precedence doesn't matter. Otherwise it's a list
operator or unary operator, and precedence does matter. And whitespace
between the function and left parenthesis doesn't count™™so you need to
be careful sometimes:
print 1+2+3; # Prints 6.
print(1+2) + 3; # Prints 3.
print (1+2)+3; # Also prints 3!
print +(1+2)+3; # Prints 6.
print ((1+2)+3); # Prints 6.
If you run Perl with the ™w switch it can warn you about this. For
example, the third line above produces:
print (...) interpreted as function at ™ line 1.
Useless use of integer addition in void context at ™ line 1.
For functions that can be used in either a scalar or list context,
non™abortive failure is generally indicated in a scalar context by
returning the undefined value, and in a list context by returning the
null list.
Remember the following rule:
·
THERE IS NO GENERAL RULE FOR CONVERTING A LIST INTO A SCALAR!
Each operator and function decides which sort of value it would be most
appropriate to return in a scalar context. Some operators return the
length of the list that would have been returned in a list context. Some
operators return the first value in the list. Some operators return the
last value in the list. Some operators return a count of successful
operations. In general, they do what you want, unless you want
consistency.
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