For delays of finer granularity than one second, you may use Perl's
four-argument version of select() leaving the first three arguments
undefined, or you might be able to use the C<syscall> interface to
-access setitimer(2) if your system supports it. The Time::HiRes module
-from CPAN may also prove useful.
+access setitimer(2) if your system supports it. The Time::HiRes
+module (from CPAN, and starting from Perl 5.8 part of the standard
+distribution) may also prove useful.
It is usually a mistake to intermix C<alarm> and C<sleep> calls.
(C<sleep> may be internally implemented in your system with C<alarm>)
platforms the external representation of C<\n> is made up of more than
one character.
-Mac OS, all variants of Unix, and Stream_LF files on VMS use a single
-character to end each line in the external representation of text (even
+Mac OS, all variants of Unix, and Stream_LF files on VMS use a single
+character to end each line in the external representation of text (even
though that single character is CARRIAGE RETURN on Mac OS and LINE FEED
-on Unix and most VMS files). Consequently binmode() has no effect on
-these operating systems. In other systems like OS/2, DOS and the various
-flavors of MS-Windows your program sees a C<\n> as a simple C<\cJ>, but
-what's stored in text files are the two characters C<\cM\cJ>. That means
-that, if you don't use binmode() on these systems, C<\cM\cJ> sequences on
-disk will be converted to C<\n> on input, and any C<\n> in your program
+on Unix and most VMS files). Consequently binmode() has no effect on
+these operating systems. In other systems like OS/2, DOS and the various
+flavors of MS-Windows your program sees a C<\n> as a simple C<\cJ>, but
+what's stored in text files are the two characters C<\cM\cJ>. That means
+that, if you don't use binmode() on these systems, C<\cM\cJ> sequences on
+disk will be converted to C<\n> on input, and any C<\n> in your program
will be converted back to C<\cM\cJ> on output. This is what you want for
text files, but it can be disastrous for binary files.
automatically convert strings into numbers as needed, this automatic
conversion assumes base 10.)
-=item open FILEHANDLE,MODE,LIST
-
=item open FILEHANDLE,EXPR
+=item open FILEHANDLE,MODE,EXPR
+
+=item open FILEHANDLE,MODE,EXPR,LIST
+
=item open FILEHANDLE
Opens the file whose filename is given by EXPR, and associates it with
-FILEHANDLE. If FILEHANDLE is an expression, its value is used as the
-name of the real filehandle wanted. (This is considered a symbolic
+FILEHANDLE. If FILEHANDLE is an undefined lexical (C<my>) variable the variable is
+assigned a reference to a new anonymous filehandle, otherwise if FILEHANDLE is an expression,
+its value is used as the name of the real filehandle wanted. (This is considered a symbolic
reference, so C<use strict 'refs'> should I<not> be in effect.)
If EXPR is omitted, the scalar
to open.) See L<perlopentut> for a kinder, gentler explanation of opening
files.
-If MODE is C<< '<' >> or nothing, the file is opened for input.
+If three or more arguments are specified then the mode of opening and the file name
+are separate. If MODE is C<< '<' >> or nothing, the file is opened for input.
If MODE is C<< '>' >>, the file is truncated and opened for
output, being created if necessary. If MODE is C<<< '>>' >>>,
the file is opened for appending, again being created if necessary.
In the 2-arguments (and 1-argument) form of the call the mode and
filename should be concatenated (in this order), possibly separated by
-spaces. It is possible to omit the mode if the mode is C<< '<' >>.
+spaces. It is possible to omit the mode in these forms if the mode is
+C<< '<' >>.
If the filename begins with C<'|'>, the filename is interpreted as a
command to which output is to be piped, and if the filename ends with a
and L<perlipc/"Bidirectional Communication with Another Process">
for alternatives.)
-If MODE is C<'|-'>, the filename is interpreted as a
+For three or more arguments if MODE is C<'|-'>, the filename is interpreted as a
command to which output is to be piped, and if MODE is
C<'-|'>, the filename is interpreted as a command which pipes output to
us. In the 2-arguments (and 1-argument) form one should replace dash
(C<'-'>) with the command. See L<perlipc/"Using open() for IPC">
for more examples of this. (You are not allowed to C<open> to a command
that pipes both in I<and> out, but see L<IPC::Open2>, L<IPC::Open3>,
-and L<perlipc/"Bidirectional Communication"> for alternatives.)
+and L<perlipc/"Bidirectional Communication"> for alternatives.) In 3+ arg form of
+pipe opens then if LIST is specified (extra arguments after the command name) then
+LIST becomes arguments to the command invoked if the platform supports it.
+The meaning of C<open> with more than three arguments for non-pipe modes
+is not yet specified. Experimental "layers" may give extra LIST arguments meaning.
In the 2-arguments (and 1-argument) form opening C<'-'> opens STDIN
and opening C<< '>-' >> opens STDOUT.
Plan9, which delimit lines with a single character, and which encode that
character in C as C<"\n">, do not need C<binmode>. The rest need it.
+In the three argument form MODE may also contain a list of IO "layers" (see L<open> and
+L<PerlIO> for more details) to be applied to the handle. This can be used to achieve the
+effect of C<binmode> as well as more complex behaviours.
+
When opening a file, it's usually a bad idea to continue normal execution
if the request failed, so C<open> is frequently used in connection with
C<die>. Even if C<die> won't do what you want (say, in a CGI script,
opens a filehandle to an anonymous temporary file.
+
Examples:
$ARTICLE = 100;
or
open(FILEHANDLE, "<&=", $fd)
-Note that if perl is using the standard C libaries fdopen() then on many UNIX systems,
+Note that if perl is using the standard C libraries fdopen() then on many UNIX systems,
fdopen() is known to fail when file descriptors
exceed a certain value, typically 255. If you need more file
descriptors than that, consider rebuilding Perl to use the C<PerlIO>.
=item our EXPR
+=item our EXPR : ATTRIBUTES
+
An C<our> declares the listed variables to be valid globals within
the enclosing block, file, or C<eval>. That is, it has the same
scoping rules as a "my" declaration, but does not create a local
our $bar; # emits warning
+An C<our> declaration may also have a list of attributes associated
+with it. B<WARNING>: This is an experimental feature that may be
+changed or removed in future releases of Perl. It should not be
+relied upon.
+
+The only currently recognized attribute is C<shared> which indicates
+that a single copy of the global is to be used by all interpreters
+should the program happen to be running in a multi-interpreter
+environment. (The default behaviour would be for each interpreter to
+have its own copy of the global.) In such an environment, this
+attribute also has the effect of making the global readonly.
+Examples:
+
+ our @EXPORT : shared = qw(foo);
+ our %EXPORT_TAGS : shared = (bar => [qw(aa bb cc)]);
+ our $VERSION : shared = "1.00";
+
+Multi-interpreter environments can come to being either through the
+fork() emulation on Windows platforms, or by embedding perl in a
+multi-threaded application. The C<shared> attribute does nothing in
+all other environments.
+
=item pack TEMPLATE,LIST
Takes a LIST of values and converts it into a string using the rules
Returns a random fractional number greater than or equal to C<0> and less
than the value of EXPR. (EXPR should be positive.) If EXPR is
-omitted, the value C<1> is used. Automatically calls C<srand> unless
-C<srand> has already been called. See also C<srand>.
+omitted, or a C<0>, the value C<1> is used. Automatically calls C<srand>
+unless C<srand> has already been called. See also C<srand>.
Apply C<int()> to the value returned by C<rand()> if you want random
integers instead of random fractional numbers. For example,
For delays of finer granularity than one second, you may use Perl's
C<syscall> interface to access setitimer(2) if your system supports
-it, or else see L</select> above. The Time::HiRes module from CPAN
-may also help.
+it, or else see L</select> above. The Time::HiRes module (from CPAN,
+and starting from Perl 5.8 part of the standard distribution) may also
+help.
See also the POSIX module's C<pause> function.
When C<use locale> is in effect, C<sort LIST> sorts LIST according to the
current collation locale. See L<perllocale>.
+Perl does B<not> guarantee that sort is stable. (A I<stable> sort
+preserves the input order of elements that compare equal.) 5.7 and
+5.8 happen to use a stable mergesort, but 5.6 and earlier used quicksort,
+which is not stable. Do not assume that future perls will continue to
+use a stable sort.
+
Examples:
# sort lexically
matching PATTERN is taken to be a delimiter separating the fields. (Note
that the delimiter may be longer than one character.)
-If LIMIT is specified and positive, splits into no more than that
-many fields (though it may split into fewer). If LIMIT is unspecified
-or zero, trailing null fields are stripped (which potential users
-of C<pop> would do well to remember). If LIMIT is negative, it is
-treated as if an arbitrarily large LIMIT had been specified.
+If LIMIT is specified and positive, it represents the maximum number
+of fields the EXPR will be split into, though the actual number of
+fields returned depends on the number of times PATTERN matches within
+EXPR. If LIMIT is unspecified or zero, trailing null fields are
+stripped (which potential users of C<pop> would do well to remember).
+If LIMIT is negative, it is treated as if an arbitrarily large LIMIT
+had been specified. Note that splitting an EXPR that evaluates to the
+empty string always returns the empty list, regardless of the LIMIT
+specified.
A pattern matching the null string (not to be confused with
a null pattern C<//>, which is just one member of the set of patterns
depending on how you look at it. Prepends list to the front of the
array, and returns the new number of elements in the array.
- unshift(ARGV, '-e') unless $ARGV[0] =~ /^-/;
+ unshift(@ARGV, '-e') unless $ARGV[0] =~ /^-/;
Note the LIST is prepended whole, not one element at a time, so the
prepended elements stay in the same order. Use C<reverse> to do the
$now = time;
utime $now, $now, @ARGV;
+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 argument.
+On most systems, this will set the file's access and modification
+times to the current time. (i.e. equivalent to the example above.)
+
+ utime undef, undef, @ARGV;
+
=item values HASH
Returns a list consisting of all the values of the named hash. (In a
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