# code
}
-The range operator also works on strings, using the magical auto-increment,
-see below.
+The range operator also works on strings, using the magical
+auto-increment, see below.
In scalar context, ".." returns a boolean value. The operator is
-bistable, like a flip-flop, and emulates the line-range (comma) operator
-of B<sed>, B<awk>, and various editors. Each ".." operator maintains its
-own boolean state. It is false as long as its left operand is false.
+bistable, like a flip-flop, and emulates the line-range (comma)
+operator of B<sed>, B<awk>, and various editors. Each ".." operator
+maintains its own boolean state, even across calls to a subroutine
+that contains it. It is false as long as its left operand is false.
Once the left operand is true, the range operator stays true until the
right operand is true, I<AFTER> which the range operator becomes false
-again. It doesn't become false till the next time the range operator is
-evaluated. It can test the right operand and become false on the same
-evaluation it became true (as in B<awk>), but it still returns true once.
-If you don't want it to test the right operand until the next
-evaluation, as in B<sed>, just use three dots ("...") instead of
+again. It doesn't become false till the next time the range operator
+is evaluated. It can test the right operand and become false on the
+same evaluation it became true (as in B<awk>), but it still returns
+true once. If you don't want it to test the right operand until the
+next evaluation, as in B<sed>, just use three dots ("...") instead of
two. In all other regards, "..." behaves just like ".." does.
The right operand is not evaluated while the operator is in the
"false" state, and the left operand is not evaluated while the
operator is in the "true" state. The precedence is a little lower
than || and &&. The value returned is either the empty string for
-false, or a sequence number (beginning with 1) for true. The
-sequence number is reset for each range encountered. The final
-sequence number in a range has the string "E0" appended to it, which
-doesn't affect its numeric value, but gives you something to search
-for if you want to exclude the endpoint. You can exclude the
-beginning point by waiting for the sequence number to be greater
-than 1.
+false, or a sequence number (beginning with 1) for true. The sequence
+number is reset for each range encountered. The final sequence number
+in a range has the string "E0" appended to it, which doesn't affect
+its numeric value, but gives you something to search for if you want
+to exclude the endpoint. You can exclude the beginning point by
+waiting for the sequence number to be greater than 1.
If either operand of scalar ".." is a constant expression,
that operand is considered true if it is equal (C<==>) to the current
=head2 Yada Yada Operator
X<...> X<... operator> X<yada yada operator>
-The yada yada operator (noted C<...>) is a placeholder for code.
-It parses without error, but when executed it throws an exception
-with the text C<Unimplemented>:
-
- sub foo { ... }
- foo();
-
- Unimplemented at <file> line <line number>.
-
-It takes no argument.
+The yada yada operator (noted C<...>) is a placeholder for code. Perl
+parses it without error, but when you try to execute a yada yada, it
+throws an exception with the text C<Unimplemented>:
+
+ sub unimplemented { ... }
+
+ eval { unimplemented() };
+ if( $@ eq 'Unimplemented' ) {
+ print "I found the yada yada!\n";
+ }
+
+You can only use the yada yada to stand in for a complete statement.
+These examples of the yada yada work:
+
+ { ... }
+
+ sub foo { ... }
+
+ ...;
+
+ eval { ... };
+
+ sub foo {
+ my( $self ) = shift;
+
+ ...;
+ }
+
+ do { my $n; ...; print 'Hurrah!' };
+
+The yada yada cannot stand in for an expression that is part of a
+larger statement since the C<...> is also the three-dot version of the
+range operator (see L<Range Operators>). These examples of the yada
+yada are still syntax errors:
+
+ print ...;
+
+ open my($fh), '>', '/dev/passwd' or ...;
+
+ if( $condition && ... ) { print "Hello\n" };
+
+There are some cases where Perl can't immediately tell the difference
+between an expression and a statement. For instance, the syntax for a
+block and an anonymous hash reference constructor look the same unless
+there's something in the braces that give Perl a hint. The yada yada
+is a syntax error if Perl doesn't guess that the C<{ ... }> is a
+block. In that case, it doesn't think the C<...> is the yada yada
+because it's expecting an expression instead of a statement:
+
+ my @transformed = map { ... } @input; # syntax error
+
+You can use a C<;> inside your block to denote that the C<{ ... }> is
+a block and not a hash reference constructor. Now the yada yada works:
+
+ my @transformed = map {; ... } @input; # ; disambiguates
+
+ my @transformed = map { ...; } @input; # ; disambiguates
=head2 List Operators (Rightward)
X<operator, list, rightward> X<list operator>
\x{263a} wide hex char (example: SMILEY)
\c[ control char (example: ESC)
\N{name} named Unicode character
+ \N{U+263D} Unicode character (example: FIRST QUARTER MOON)
The character following C<\c> is mapped to some other character by
converting letters to upper case and then (on ASCII systems) by inverting
'@', the letters, '[', '\', ']', '^', '_' and '?' will work, resulting
in 0x00 through 0x1F and 0x7F.
-B<NOTE>: Unlike C and other languages, Perl has no \v escape sequence for
-the vertical tab (VT - ASCII 11), but you may use C<\ck> or C<\x0b>.
+C<\N{U+I<wide hex char>}> means the Unicode character whose Unicode ordinal
+number is I<wide hex char>.
+For documentation of C<\N{name}>, see L<charnames>.
-The following escape sequences are available in constructs that interpolate
+B<NOTE>: Unlike C and other languages, Perl has no C<\v> escape sequence for
+the vertical tab (VT - ASCII 11), but you may use C<\ck> or C<\x0b>. (C<\v>
+does have meaning in regular expression patterns in Perl, see L<perlre>.)
+
+The following escape sequences are available in constructs that interpolate,
but not in transliterations.
X<\l> X<\u> X<\L> X<\U> X<\E> X<\Q>
C<\u> and C<\U> is taken from the current locale. See L<perllocale>.
If Unicode (for example, C<\N{}> or wide hex characters of 0x100 or
beyond) is being used, the case map used by C<\l>, C<\L>, C<\u> and
-C<\U> is as defined by Unicode. For documentation of C<\N{name}>,
-see L<charnames>.
+C<\U> is as defined by Unicode.
All systems use the virtual C<"\n"> to represent a line terminator,
called a "newline". There is no such thing as an unvarying, physical
Notice that the final match matched C<q> instead of C<p>, which a match
without the C<\G> anchor would have done. Also note that the final match
-did not update C<pos> -- C<pos> is only updated on a C</g> match. If the
+did not update C<pos>. C<pos> is only updated on a C</g> match. If the
final match did indeed match C<p>, it's a good bet that you're running an
older (pre-5.6.0) Perl.
warning B<Can't find string terminator "END" anywhere before EOF...>.
Additionally, the quoting rules for the end of string identifier are not
-related to Perl's quoting rules -- C<q()>, C<qq()>, and the like are not
+related to Perl's quoting rules. C<q()>, C<qq()>, and the like are not
supported in place of C<''> and C<"">, and the only interpolation is for
backslashing the quoting character:
Processing of C<\Q>, C<\U>, C<\u>, C<\L>, C<\l>, C<\E>,
and interpolation happens (almost) as with C<qq//> constructs.
+Processing of C<\N{...}> is also done here, and compiled into an intermediate
+form for the regex compiler. (This is because, as mentioned below, the regex
+compilation may be done at execution time, and C<\N{...}> is a compile-time
+construct.)
+
However any other combinations of C<\> followed by a character
are not substituted but only skipped, in order to parse them
as regular expressions at the following step.
X<regexp, parse>
Previous steps were performed during the compilation of Perl code,
-but this one happens at run time--although it may be optimized to
+but this one happens at run time, although it may be optimized to
be calculated at compile time if appropriate. After preprocessing
described above, and possibly after evaluation if concatenation,
joining, casing translation, or metaquoting are involved, the
except that it isn't so cumbersome to say, and will actually work.
It really does shift the @ARGV array and put the current filename
into the $ARGV variable. It also uses filehandle I<ARGV>
-internally--<> is just a synonym for <ARGV>, which
+internally. <> is just a synonym for <ARGV>, which
is magical. (The pseudo code above doesn't work because it treats
<ARGV> as non-magical.)
printf "%.20g\n", 123456789123456789;
# produces 123456789123456784
-Testing for exact equality of floating-point equality or inequality is
-not a good idea. Here's a (relatively expensive) work-around to compare
+Testing for exact floating-point equality or inequality is not a
+good idea. Here's a (relatively expensive) work-around to compare
whether two floating-point numbers are equal to a particular number of
decimal places. See Knuth, volume II, for a more robust treatment of
this topic.
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