If LAYER is omitted or specified as C<:raw> the filehandle is made
suitable for passing binary data. This includes turning off possible CRLF
translation and marking it as bytes (as opposed to Unicode characters).
-Note that as despite what may be implied in I<"Programming Perl">
-(the Camel) or elsewhere C<:raw> is I<not> the simply inverse of C<:crlf>
+Note that, despite what may be implied in I<"Programming Perl"> (the
+Camel) or elsewhere, C<:raw> is I<not> the simply inverse of C<:crlf>
-- other layers which would affect binary nature of the stream are
I<also> disabled. See L<PerlIO>, L<perlrun> and the discussion about the
PERLIO environment variable.
Returns the character represented by that NUMBER in the character set.
For example, C<chr(65)> is C<"A"> in either ASCII or Unicode, and
-chr(0x263a) is a Unicode smiley face. Note that characters from 127
-to 255 (inclusive) are by default not encoded in Unicode for backward
-compatibility reasons (but see L<encoding>).
+chr(0x263a) is a Unicode smiley face. Note that characters from 128
+to 255 (inclusive) are by default not encoded in UTF-8 Unicode for
+backward compatibility reasons (but see L<encoding>).
If NUMBER is omitted, uses C<$_>.
doesn't implement fcntl(2). See the Fcntl module or your fcntl(2)
manpage to learn what functions are available on your system.
+Here's an example of setting a filehandle named C<REMOTE> to be
+non-blocking at the system level. You'll have to negotiate C<$|>
+on your own, though.
+
+ use Fcntl qw(F_GETFL F_SETFL O_NONBLOCK);
+
+ $flags = fcntl(REMOTE, F_GETFL, 0)
+ or die "Can't get flags for the socket: $!\n";
+
+ $flags = fcntl(REMOTE, F_SETFL, $flags | O_NONBLOCK)
+ or die "Can't set flags for the socket: $!\n";
+
=item fileno FILEHANDLE
Returns the file descriptor for a filehandle, or undefined if the
$retval = ioctl(...) || -1;
printf "System returned %d\n", $retval;
-The special string "C<0> but true" is exempt from B<-w> complaints
+The special string C<"0 but true"> is exempt from B<-w> complaints
about improper numeric conversions.
-Here's an example of setting a filehandle named C<REMOTE> to be
-non-blocking at the system level. You'll have to negotiate C<$|>
-on your own, though.
-
- use Fcntl qw(F_GETFL F_SETFL O_NONBLOCK);
-
- $flags = fcntl(REMOTE, F_GETFL, 0)
- or die "Can't get flags for the socket: $!\n";
-
- $flags = fcntl(REMOTE, F_SETFL, $flags | O_NONBLOCK)
- or die "Can't set flags for the socket: $!\n";
-
=item join EXPR,LIST
Joins the separate strings of LIST into a single string with fields
Attacks">).
As a side effect, calling keys() resets the HASH's internal iterator,
-see L</each>.
+see L</each>. (In particular, calling keys() in void context resets
+the iterator with no other overhead.)
Here is yet another way to print your environment:
=item *
-If the pattern begins with a C<U>, the resulting string will be treated
-as Unicode-encoded. You can force UTF8 encoding on in a string with an
-initial C<U0>, and the bytes that follow will be interpreted as Unicode
-characters. If you don't want this to happen, you can begin your pattern
-with C<C0> (or anything else) to force Perl not to UTF8 encode your
-string, and then follow this with a C<U*> somewhere in your pattern.
+If the pattern begins with a C<U>, the resulting string will be
+treated as UTF-8-encoded Unicode. You can force UTF-8 encoding on in a
+string with an initial C<U0>, and the bytes that follow will be
+interpreted as Unicode characters. If you don't want this to happen,
+you can begin your pattern with C<C0> (or anything else) to force Perl
+not to UTF-8 encode your string, and then follow this with a C<U*>
+somewhere in your pattern.
=item *
=item ref
-Returns a true value if EXPR is a reference, false otherwise. If EXPR
+Returns a non-empty string if EXPR is a reference, the empty
+string otherwise. If EXPR
is not specified, C<$_> will be used. The value returned depends on the
type of thing the reference is a reference to.
Builtin types include:
Otherwise, demands that a library file be included if it hasn't already
been included. The file is included via the do-FILE mechanism, which is
-essentially just a variety of C<eval>. Has semantics similar to the following
-subroutine:
+essentially just a variety of C<eval>. Has semantics similar to the
+following subroutine:
sub require {
- my($filename) = @_;
- return 1 if $INC{$filename};
- my($realfilename,$result);
- ITER: {
- foreach $prefix (@INC) {
- $realfilename = "$prefix/$filename";
- if (-f $realfilename) {
- $INC{$filename} = $realfilename;
- $result = do $realfilename;
- last ITER;
- }
- }
- die "Can't find $filename in \@INC";
- }
- delete $INC{$filename} if $@ || !$result;
- die $@ if $@;
- die "$filename did not return true value" unless $result;
- return $result;
+ my ($filename) = @_;
+ if (exists $INC{$filename}) {
+ return 1 if $INC{$filename};
+ die "Compilation failed in require";
+ }
+ my ($realfilename,$result);
+ ITER: {
+ foreach $prefix (@INC) {
+ $realfilename = "$prefix/$filename";
+ if (-f $realfilename) {
+ $INC{$filename} = $realfilename;
+ $result = do $realfilename;
+ last ITER;
+ }
+ }
+ die "Can't find $filename in \@INC";
+ }
+ if ($@) {
+ $INC{$filename} = undef;
+ die $@;
+ } elsif (!$result) {
+ delete $INC{$filename};
+ die "$filename did not return true value";
+ } else {
+ return $result;
+ }
}
Note that the file will not be included twice under the same specified
-name. The file must return true as the last statement to indicate
+name.
+
+The file must return true as the last statement to indicate
successful execution of any initialization code, so it's customary to
end such a file with C<1;> unless you're sure it'll return true
otherwise. But it's better just to put the C<1;>, in case you add more
You can check all the failure possibilities by inspecting
C<$?> like this:
- $exit_value = $? >> 8;
- $signal_num = $? & 127;
- $dumped_core = $? & 128;
+ if ($? == -1) {
+ print "failed to execute: $!\n";
+ }
+ elsif ($? & 127) {
+ printf "child died with signal %d, %s coredump\n",
+ ($? & 127), ($? & 128) ? 'with' : 'without';
+ }
+ else {
+ printf "child exited with value %d\n", $? >> 8;
+ }
+
or more portably by using the W*() calls of the POSIX extension;
see L<perlport> for more information.
EXISTS this, key
FIRSTKEY this
NEXTKEY this, lastkey
+ SCALAR this
DESTROY this
UNTIE this
Unix touch(1) command when the files I<already exist>.
#!/usr/bin/perl
- $now = time;
- utime $now, $now, @ARGV;
-
-B<Note:> Under NFS, touch(1) uses the time of the NFS server, not
-the time of the local machine. If there is a time synchronization
-problem, the NFS server and local machine will have different times.
+ $atime = $mtime = time;
+ utime $atime, $mtime, @ARGV;
Since perl 5.7.2, if the first two elements of the list are C<undef>, then
the utime(2) function in the C library will be called with a null second
utime undef, undef, @ARGV;
+Under NFS this will use the time of the NFS server, not the time of
+the local machine. If there is a time synchronization problem, the
+NFS server and local machine will have different times. The Unix
+touch(1) command will in fact normally use this form instead of the
+one shown in the first example.
+
+Note that only passing one of the first two elements as C<undef> will
+be equivalent of passing it as 0 and will not have the same effect as
+described when they are both C<undef>. This case will also trigger an
+uninitialized warning.
+
=item values HASH
Returns a list consisting of all the values of the named hash.
for security reasons (see L<perlsec/"Algorithmic Complexity Attacks">).
As a side effect, calling values() resets the HASH's internal iterator,
-see L</each>.
+see L</each>. (In particular, calling values() in void context resets
+the iterator with no other overhead.)
Note that the values are not copied, which means modifying them will
modify the contents of the hash:
to try to write off the beginning of the string (i.e. negative OFFSET).
The string should not contain any character with the value > 255 (which
-can only happen if you're using UTF8 encoding). If it does, it will be
-treated as something which is not UTF8 encoded. When the C<vec> was
+can only happen if you're using UTF-8 encoding). If it does, it will be
+treated as something which is not UTF-8 encoded. When the C<vec> was
assigned to, other parts of your program will also no longer consider the
-string to be UTF8 encoded. In other words, if you do have such characters
+string to be UTF-8 encoded. In other words, if you do have such characters
in your string, vec() will operate on the actual byte string, and not the
conceptual character string.
projects / p5sagit/p5-mst-13.2.git / blobdiff