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A
TERM has the highest precedence in Perl. They includes variables, quote and quote-like operators, any expression in parentheses, and any function whose arguments are parenthesized. Actually, there aren't really functions in this sense, just list operators and unary operators behaving as functions because you put parentheses around the arguments. These are all documented in
the perlfunc manpage.
If any list operator (print(), etc.) or any unary operator (chdir(), etc.)
is followed by a left parenthesis as the next token, the operator and
arguments within parentheses are taken to be of highest precedence, just
like a normal function call.
In the absence of parentheses, the precedence of list operators such as
print, sort, or chmod is either very high or very low depending on whether you are looking at the
left side or the right side of the operator. For example, in
@ary = (1, 3, sort 4, 2);
print @ary; # prints 1324
the commas on the right of the sort are evaluated before the sort, but the commas on the left are evaluated after. In other words, list operators tend to gobble up all the arguments that follow them, and then act like a simple
TERM with regard to the preceding expression. Note that you have to be careful with parentheses:
# These evaluate exit before doing the print:
print($foo, exit); # Obviously not what you want.
print $foo, exit; # Nor is this.
# These do the print before evaluating exit:
(print $foo), exit; # This is what you want.
print($foo), exit; # Or this.
print ($foo), exit; # Or even this.
Also note that
print ($foo & 255) + 1, "\n";
probably doesn't do what you expect at first glance. See
Named Unary Operators for more discussion of this.
Also parsed as terms are the do {} and eval {} constructs, as well as subroutine and method calls, and the anonymous
constructors [] and {} .
See also Quote and Quote-like Operators toward the end of this section, as well as I/O Operators.
Source: Perl operators and precedence Copyright: Larry Wall, et al. |
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