=head2 The Arrow Operator
-"C<-E<gt>>" is an infix dereference operator, just as it is in C
+"C<< -> >>" is an infix dereference operator, just as it is in C
and C++. If the right side is either a C<[...]>, C<{...}>, or a
C<(...)> subscript, then the left side must be either a hard or
symbolic reference to an array, a hash, or a subroutine respectively.
is returned. One effect of these rules is that C<-bareword> is equivalent
to C<"-bareword">.
-Unary "~" performs bitwise negation, i.e., 1's complement. For example,
-C<0666 &~ 027> is 0640. (See also L<Integer Arithmetic> and L<Bitwise
-String Operators>.)
+Unary "~" performs bitwise negation, i.e., 1's complement. For
+example, C<0666 & ~027> is 0640. (See also L<Integer Arithmetic> and
+L<Bitwise String Operators>.) Note that the width of the result is
+platform-dependent: ~0 is 32 bits wide on a 32-bit platform, but 64
+bits wide on a 64-bit platform, so if you are expecting a certain bit
+width, remember use the & operator to mask off the excess bits.
Unary "+" has no effect whatsoever, even on strings. It is useful
syntactically for separating a function name from a parenthesized expression
of operation work on some other string. The right argument is a search
pattern, substitution, or transliteration. The left argument is what is
supposed to be searched, substituted, or transliterated instead of the default
-$_. The return value indicates the success of the operation. (If the
-right argument is an expression rather than a search pattern,
+$_. When used in scalar context, the return value generally indicates the
+success of the operation. Behavior in list context depends on the particular
+operator. See L</"Regexp Quote-Like Operators"> for details.
+
+If the right argument is an expression rather than a search pattern,
substitution, or transliteration, it is interpreted as a search pattern at run
-time. This can be is less efficient than an explicit search, because the
-pattern must be compiled every time the expression is evaluated).
+time. This can be less efficient than an explicit search, because the
+pattern must be compiled every time the expression is evaluated.
Binary "!~" is just like "=~" except the return value is negated in
the logical sense.
=head2 Relational Operators
-Binary "E<lt>" returns true if the left argument is numerically less than
+Binary "<" returns true if the left argument is numerically less than
the right argument.
-Binary "E<gt>" returns true if the left argument is numerically greater
+Binary ">" returns true if the left argument is numerically greater
than the right argument.
-Binary "E<lt>=" returns true if the left argument is numerically less than
+Binary "<=" returns true if the left argument is numerically less than
or equal to the right argument.
-Binary "E<gt>=" returns true if the left argument is numerically greater
+Binary ">=" returns true if the left argument is numerically greater
than or equal to the right argument.
Binary "lt" returns true if the left argument is stringwise less than
Binary "!=" returns true if the left argument is numerically not equal
to the right argument.
-Binary "E<lt>=E<gt>" returns -1, 0, or 1 depending on whether the left
+Binary "<=>" returns -1, 0, or 1 depending on whether the left
argument is numerically less than, equal to, or greater than the right
argument.
unlink("alpha", "beta", "gamma")
|| (gripe(), next LINE);
-Use "or" for assignment is unlikely to do what you want; see below.
+Using "or" for assignment is unlikely to do what you want; see below.
=head2 Range Operators
In list context, it's just the list argument separator, and inserts
both its arguments into the list.
-The =E<gt> digraph is mostly just a synonym for the comma operator. It's useful for
+The => digraph is mostly just a synonym for the comma operator. It's useful for
documenting arguments that come in pairs. As of release 5.001, it also forces
any word to the left of it to be interpreted as a string.
that
q{foo{bar}baz}
-
+
is the same as
'foo{bar}baz'
and is useful when the value you are interpolating won't change over
the life of the script. However, mentioning C</o> constitutes a promise
that you won't change the variables in the pattern. If you change them,
-Perl won't even notice. See also L<qr//>.
+Perl won't even notice. See also L<"qr//">.
If the PATTERN evaluates to the empty string, the last
I<successfully> matched regular expression is used instead.
my @compiled = map qr/$_/i, @$patterns;
grep {
my $success = 0;
- foreach my $pat @compiled {
+ foreach my $pat (@compiled) {
$success = 1, last if /$pat/;
}
$success;
qw(foo bar baz)
-is exactly equivalent to the list:
+is semantically equivalent to the list:
- ('foo', 'bar', 'baz')
+ 'foo', 'bar', 'baz'
Some frequently seen examples:
text is not evaluated as a command. If the
PATTERN is delimited by bracketing quotes, the REPLACEMENT has its own
pair of quotes, which may or may not be bracketing quotes, e.g.,
-C<s(foo)(bar)> or C<sE<lt>fooE<gt>/bar/>. A C</e> will cause the
+C<s(foo)(bar)> or C<< s<foo>/bar/ >>. A C</e> will cause the
replacement portion to be interpreted as a full-fledged Perl expression
and eval()ed right then and there. It is, however, syntax checked at
compile-time.
s/([^ ]*) *([^ ]*)/$2 $1/; # reverse 1st two fields
Note the use of $ instead of \ in the last example. Unlike
-B<sed>, we use the \E<lt>I<digit>E<gt> form in only the left hand side.
-Anywhere else it's $E<lt>I<digit>E<gt>.
+B<sed>, we use the \<I<digit>> form in only the left hand side.
+Anywhere else it's $<I<digit>>.
Occasionally, you can't use just a C</g> to get all the changes
to occur that you might want. Here are two common cases:
The first pass is finding the end of the quoted construct, whether
it be a multicharacter delimiter C<"\nEOF\n"> in the C<<<EOF>
construct, a C</> that terminates a C<qq//> construct, a C<]> which
-terminates C<qq[]> construct, or a C<E<gt>> which terminates a
-fileglob started with C<E<lt>>.
+terminates C<qq[]> construct, or a C<< > >> which terminates a
+fileglob started with C<< < >>.
When searching for single-character non-pairing delimiters, such
as C</>, combinations of C<\\> and C<\/> are skipped. However,
The only interpolation is removal of C<\> from pairs C<\\>.
-=item C<"">, C<``>, C<qq//>, C<qx//>, C<<file*globE<gt>>
+=item C<"">, C<``>, C<qq//>, C<qx//>, C<< <file*glob> >>
C<\Q>, C<\U>, C<\u>, C<\L>, C<\l> (possibly paired with C<\E>) are
converted to corresponding Perl constructs. Thus, C<"$foo\Qbaz$bar">
Note also that the interpolation code needs to make a decision on
where the interpolated scalar ends. For instance, whether
-C<"a $b -E<gt> {c}"> really means:
+C<< "a $b -> {c}" >> really means:
"a " . $b . " -> {c}";
while (($_ = <STDIN>) ne '0') { ... }
while (<STDIN>) { last unless $_; ... }
-In other boolean contexts, C<E<lt>I<filehandle>E<gt>> without an
+In other boolean contexts, C<< <I<filehandle>> >> without an
explicit C<defined> test or comparison elicit a warning if the B<-w>
command-line switch (the C<$^W> variable) is in effect.
the open() function, amongst others. See L<perlopentut> and
L<perlfunc/open> for details on this.
-If a E<lt>FILEHANDLEE<gt> is used in a context that is looking for
+If a <FILEHANDLE> is used in a context that is looking for
a list, a list comprising all input lines is returned, one line per
list element. It's easy to grow to a rather large data space this
way, so use with care.
-E<lt>FILEHANDLEE<gt> may also be spelled C<readline(*FILEHANDLE)>.
+<FILEHANDLE> may also be spelled C<readline(*FILEHANDLE)>.
See L<perlfunc/readline>.
-The null filehandle E<lt>E<gt> is special: it can be used to emulate the
-behavior of B<sed> and B<awk>. Input from E<lt>E<gt> comes either from
+The null filehandle <> is special: it can be used to emulate the
+behavior of B<sed> and B<awk>. Input from <> comes either from
standard input, or from each file listed on the command line. Here's
-how it works: the first time E<lt>E<gt> is evaluated, the @ARGV array is
+how it works: the first time <> is evaluated, the @ARGV array is
checked, and if it is empty, C<$ARGV[0]> is set to "-", which when opened
gives you standard input. The @ARGV array is then processed as a list
of filenames. The loop
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 $ARGV variable. It also uses filehandle I<ARGV>
-internally--E<lt>E<gt> is just a synonym for E<lt>ARGVE<gt>, which
+internally--<> is just a synonym for <ARGV>, which
is magical. (The pseudo code above doesn't work because it treats
-E<lt>ARGVE<gt> as non-magical.)
+<ARGV> as non-magical.)
-You can modify @ARGV before the first E<lt>E<gt> as long as the array ends up
+You can modify @ARGV before the first <> as long as the array ends up
containing the list of filenames you really want. Line numbers (C<$.>)
continue as though the input were one big happy file. See the example
in L<perlfunc/eof> for how to reset line numbers on each file.
# ... # code for each line
}
-The E<lt>E<gt> symbol will return C<undef> for end-of-file only once.
+The <> symbol will return C<undef> for end-of-file only once.
If you call it again after this, it will assume you are processing another
@ARGV list, and if you haven't set @ARGV, will read input from STDIN.
If angle brackets contain is a simple scalar variable (e.g.,
-E<lt>$fooE<gt>), then that variable contains the name of the
+<$foo>), then that variable contains the name of the
filehandle to input from, or its typeglob, or a reference to the
same. For example:
reference, it is interpreted as a filename pattern to be globbed, and
either a list of filenames or the next filename in the list is returned,
depending on context. This distinction is determined on syntactic
-grounds alone. That means C<E<lt>$xE<gt>> is always a readline() from
-an indirect handle, but C<E<lt>$hash{key}E<gt>> is always a glob().
+grounds alone. That means C<< <$x> >> is always a readline() from
+an indirect handle, but C<< <$hash{key}> >> is always a glob().
That's because $x is a simple scalar variable, but C<$hash{key}> is
not--it's a hash element.
One level of double-quote interpretation is done first, but you can't
-say C<E<lt>$fooE<gt>> because that's an indirect filehandle as explained
+say C<< <$foo> >> because that's an indirect filehandle as explained
in the previous paragraph. (In older versions of Perl, programmers
would insert curly brackets to force interpretation as a filename glob:
-C<E<lt>${foo}E<gt>>. These days, it's considered cleaner to call the
+C<< <${foo}> >>. These days, it's considered cleaner to call the
internal function directly as C<glob($foo)>, which is probably the right
way to have done it in the first place.) For example:
chmod 0644, $_;
}
-is equivalent to
+is roughly equivalent to:
open(FOO, "echo *.c | tr -s ' \t\r\f' '\\012\\012\\012\\012'|");
while (<FOO>) {
chmod 0644, $_;
}
-In fact, it's currently implemented that way, but this is expected
-to be made completely internal in the near future. (Which means
-it will not work on filenames with spaces in them unless you have
-csh(1) on your machine.) Of course, the shortest way to do the
-above is:
+except that the globbing is actually done internally using the standard
+C<File::Glob> extension. Of course, the shortest way to do the above is:
chmod 0644, <*.c>;
-Because globbing currently invokes a shell, it's often faster to
-call readdir() yourself and do your own grep() on the filenames.
-Furthermore, due to its current implementation of using a shell,
-the glob() routine may get "Arg list too long" errors (unless you've
-installed tcsh(1L) as F</bin/csh> or hacked your F<config.sh>).
-
A (file)glob evaluates its (embedded) argument only when it is
starting a new list. All values must be read before it will start
over. In list context, this isn't important because you automatically
The non-standard modules SSLeay::BN and Math::Pari provide
equivalent functionality (and much more) with a substantial
performance savings.
+
+=cut
projects / p5sagit/p5-mst-13.2.git / blobdiff