This chapter gives a brief description of Perl’s built-in functions. Each description gives the syntax of the function, with the types and order of its arguments .

Required arguments are shown in italics, separated by commas. If an argument must be a specific variable type, that variable’s identifier will be used (e.g., a percent sign for a hash, % hash). Optional arguments are placed in brackets. Do not use the brackets in function calls unless you really want to use an anonymous hash reference.

There are different ways to use a built-in function. For starters, any argument that requires a scalar value can be made up of any expression that returns one. For example, you can obtain the square root of the first value in an array:

$root = sqrt (shift @numbers);

shift removes the first element of @numbers and returns it to be used by sqrt.

Many functions take a list of scalars for arguments. Any array variable or other expression that returns a list can be used for all or part of the arguments. For example:

chmod (split /,/ FILELIST>); # An expression returns a list
chmod 0755, @executables;    # Array used for part of arguments

In the first line, the split expression reads a string from a filehandle and splits it into a list. The list provides proper arguments for chmod. The second line uses an array that contains a list of filenames for chmod to act upon.

Parentheses are not required around a function’s arguments. However, without parentheses, functions are viewed as operators in an expression (the same is true of predeclared subroutines). If you use a function in a complex expression, you may want to use parentheses for clarity. See Chapter 4 for more about precedence in Perl expressions.