does. Returns the packed address if it succeeded, false otherwise.
See the example in L<perlipc/"Sockets: Client/Server Communication">.
+On systems that support a close-on-exec flag on files, the flag will
+be set for the newly opened file descriptor, as determined by the
+value of $^F. See L<perlvar/$^F>.
+
=item alarm SECONDS
=item alarm
Returns the arctangent of Y/X in the range -PI to PI.
-For the tangent operation, you may use the C<POSIX::tan()>
+For the tangent operation, you may use the C<Math::Trig::tan>
function, or use the familiar relation:
sub tan { sin($_[0]) / cos($_[0]) }
to go back before the current one.
($package, $filename, $line, $subroutine, $hasargs,
- $wantarray, $evaltext, $is_require, $hints) = caller($i);
+ $wantarray, $evaltext, $is_require, $hints, $bitmask) = caller($i);
-Here $subroutine may be C<"(eval)"> if the frame is not a subroutine
+Here $subroutine may be C<(eval)> if the frame is not a subroutine
call, but an C<eval>. In such a case additional elements $evaltext and
C<$is_require> are set: C<$is_require> is true if the frame is created by a
C<require> or C<use> statement, $evaltext contains the text of the
C<eval EXPR> statement. In particular, for a C<eval BLOCK> statement,
-$filename is C<"(eval)">, but $evaltext is undefined. (Note also that
+$filename is C<(eval)>, but $evaltext is undefined. (Note also that
each C<use> statement creates a C<require> frame inside an C<eval EXPR>)
-frame. C<$hints> contains pragmatic hints that the caller was
-compiled with. It currently only reflects the hint corresponding to
-C<use utf8>.
+frame. C<$hints> and C<$bitmask> contain pragmatic hints that the caller
+was compiled with. The C<$hints> and C<$bitmask> values are subject to
+change between versions of Perl, and are not meant for external use.
Furthermore, when called from within the DB package, caller returns more
detailed information: it sets the list variable C<@DB::args> to be the
=item chdir EXPR
Changes the working directory to EXPR, if possible. If EXPR is omitted,
-changes to the user's home directory. Returns true upon success,
-false otherwise. See the example under C<die>.
+changes to the directory specified by C<$ENV{HOME}>, if set; if not,
+changes to the directory specified by C<$ENV{LOGDIR}>. If neither is
+set, C<chdir> does nothing. It returns true upon success, false
+otherwise. See the example under C<die>.
=item chmod LIST
$mode = '0644'; chmod oct($mode), 'foo'; # this is better
$mode = 0644; chmod $mode, 'foo'; # this is best
+You can also import the symbolic C<S_I*> constants from the Fcntl
+module:
+
+ use Fcntl ':mode';
+
+ chmod S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH, @executables;
+ # This is identical to the chmod 0755 of the above example.
+
=item chomp VARIABLE
=item chomp LIST
This function works like the system call by the same name: it makes the
named directory the new root directory for all further pathnames that
-begin with a C<"/"> by your process and all its children. (It doesn't
+begin with a C</> by your process and all its children. (It doesn't
change your current working directory, which is unaffected.) For security
reasons, this call is restricted to the superuser. If FILENAME is
omitted, does a C<chroot> to C<$_>.
Returns the cosine of EXPR (expressed in radians). If EXPR is omitted,
takes cosine of C<$_>.
-For the inverse cosine operation, you may use the C<POSIX::acos()>
+For the inverse cosine operation, you may use the C<Math::Trig::acos()>
function, or use this relation:
sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) }
=item delete EXPR
-Deletes the specified key(s) and their associated values from a hash.
-For each key, returns the deleted value associated with that key, or
-the undefined value if there was no such key. Deleting from C<$ENV{}>
-modifies the environment. Deleting from a hash tied to a DBM file
-deletes the entry from the DBM file. (But deleting from a C<tie>d hash
-doesn't necessarily return anything.)
+Given an expression that specifies a hash element, array element, hash slice,
+or array slice, deletes the specified element(s) from the hash or array.
+In the case of an array, if the array elements happen to be at the end,
+the size of the array will shrink to the highest element that tests
+true for exists() (or 0 if no such element exists).
-The following deletes all the values of a hash:
+Returns each element so deleted or the undefined value if there was no such
+element. Deleting from C<$ENV{}> modifies the environment. Deleting from
+a hash tied to a DBM file deletes the entry from the DBM file. Deleting
+from a C<tie>d hash or array may not necessarily return anything.
+
+Deleting an array element effectively returns that position of the array
+to its initial, uninitialized state. Subsequently testing for the same
+element with exists() will return false. Note that deleting array
+elements in the middle of an array will not shift the index of the ones
+after them down--use splice() for that. See L</exists>.
+
+The following (inefficiently) deletes all the values of %HASH and @ARRAY:
foreach $key (keys %HASH) {
delete $HASH{$key};
}
-And so does this:
+ foreach $index (0 .. $#ARRAY) {
+ delete $ARRAY[$index];
+ }
+
+And so do these:
- delete @HASH{keys %HASH}
+ delete @HASH{keys %HASH};
+
+ delete @ARRAY[0 .. $#ARRAY];
But both of these are slower than just assigning the empty list
-or undefining it:
+or undefining %HASH or @ARRAY:
+
+ %HASH = (); # completely empty %HASH
+ undef %HASH; # forget %HASH ever existed
- %hash = (); # completely empty %hash
- undef %hash; # forget %hash every existed
+ @ARRAY = (); # completely empty @ARRAY
+ undef @ARRAY; # forget @ARRAY ever existed
Note that the EXPR can be arbitrarily complicated as long as the final
-operation is a hash element lookup or hash slice:
+operation is a hash element, array element, hash slice, or array slice
+lookup:
delete $ref->[$x][$y]{$key};
delete @{$ref->[$x][$y]}{$key1, $key2, @morekeys};
+ delete $ref->[$x][$y][$index];
+ delete @{$ref->[$x][$y]}[$index1, $index2, @moreindices];
+
=item die LIST
Outside an C<eval>, prints the value of LIST to C<STDERR> and
When called in list context, returns a 2-element list consisting of the
key and value for the next element of a hash, so that you can iterate over
it. When called in scalar context, returns the key for only the "next"
-element in the hash. (Note: Keys may be C<"0"> or C<"">, which are logically
-false; you may wish to avoid constructs like C<while ($k = each %foo) {}>
-for this reason.)
+element in the hash.
Entries are returned in an apparently random order. The actual random
order is subject to change in future versions of perl, but it is guaranteed
C<eof(FILEHANDLE)> on it) after end-of-file is reached. File types such
as terminals may lose the end-of-file condition if you do.
-An C<eof> without an argument uses the last file read as argument.
-Using C<eof()> with empty parentheses is very different. It indicates
-the pseudo file formed of the files listed on the command line,
-i.e., C<eof()> is reasonable to use inside a C<while (E<lt>E<gt>)>
-loop to detect the end of only the last file. Use C<eof(ARGV)> or
-C<eof> without the parentheses to test I<each> file in a while
-(E<lt>E<gt>) loop. Examples:
+An C<eof> without an argument uses the last file read. Using C<eof()>
+with empty parentheses is very different. It refers to the pseudo file
+formed from the files listed on the command line and accessed via the
+C<E<lt>E<gt>> operator. Since C<E<lt>E<gt>> isn't explicitly opened,
+as a normal filehandle is, an C<eof()> before C<E<lt>E<gt>> has been
+used will cause C<@ARGV> to be examined to determine if input is
+available.
+
+In a C<while (E<lt>E<gt>)> loop, C<eof> or C<eof(ARGV)> can be used to
+detect the end of each file, C<eof()> will only detect the end of the
+last file. Examples:
# reset line numbering on each input file
while (<>) {
}
Practical hint: you almost never need to use C<eof> in Perl, because the
-input operators return false values when they run out of data, or if there
-was an error.
+input operators typically return C<undef> when they run out of data, or if
+there was an error.
=item eval EXPR
=item exists EXPR
-Returns true if the specified hash key exists in its hash, even
-if the corresponding value is undefined.
+Given an expression that specifies a hash element or array element,
+returns true if the specified element in the hash or array has ever
+been initialized, even if the corresponding value is undefined. The
+element is not autovivified if it doesn't exist.
- print "Exists\n" if exists $array{$key};
- print "Defined\n" if defined $array{$key};
- print "True\n" if $array{$key};
+ print "Exists\n" if exists $hash{$key};
+ print "Defined\n" if defined $hash{$key};
+ print "True\n" if $hash{$key};
-A hash element can be true only if it's defined, and defined if
+ print "Exists\n" if exists $array[$index];
+ print "Defined\n" if defined $array[$index];
+ print "True\n" if $array[$index];
+
+A hash or array element can be true only if it's defined, and defined if
it exists, but the reverse doesn't necessarily hold true.
+Given an expression that specifies the name of a subroutine,
+returns true if the specified subroutine has ever been declared, even
+if it is undefined. Mentioning a subroutine name for exists or defined
+does not count as declaring it.
+
+ print "Exists\n" if exists &subroutine;
+ print "Defined\n" if defined &subroutine;
+
Note that the EXPR can be arbitrarily complicated as long as the final
-operation is a hash key lookup:
+operation is a hash or array key lookup or subroutine name:
if (exists $ref->{A}->{B}->{$key}) { }
if (exists $hash{A}{B}{$key}) { }
-Although the last element will not spring into existence just because
-its existence was tested, intervening ones will. Thus C<$ref-E<gt>{"A"}>
-and C<$ref-E<gt>{"A"}-E<gt>{"B"}> will spring into existence due to the
-existence test for a $key element. This happens anywhere the arrow
-operator is used, including even
+ if (exists $ref->{A}->{B}->[$ix]) { }
+ if (exists $hash{A}{B}[$ix]) { }
+
+ if (exists &{$ref->{A}{B}{$key}}) { }
+
+Although the deepest nested array or hash will not spring into existence
+just because its existence was tested, any intervening ones will.
+Thus C<$ref-E<gt>{"A"}> and C<$ref-E<gt>{"A"}-E<gt>{"B"}> will spring
+into existence due to the existence test for the $key element above.
+This happens anywhere the arrow operator is used, including even:
undef $ref;
if (exists $ref->{"Some key"}) { }
second--glance appear to be an lvalue context may be fixed in a future
release.
+See L<perlref/"Pseudo-hashes"> for specifics on how exists() acts when
+used on a pseudo-hash.
+
+Use of a subroutine call, rather than a subroutine name, as an argument
+to exists() is an error.
+
+ exists ⊂ # OK
+ exists &sub(); # Error
+
=item exit EXPR
Evaluates EXPR and exits immediately with that value. Example:
or die "can't fcntl F_GETFL: $!";
You don't have to check for C<defined> on the return from C<fnctl>.
-Like C<ioctl>, it maps a C<0> return from the system call into C<"0
-but true"> in Perl. This string is true in boolean context and C<0>
+Like C<ioctl>, it maps a C<0> return from the system call into
+C<"0 but true"> in Perl. This string is true in boolean context and C<0>
in numeric context. It is also exempt from the normal B<-w> warnings
on improper numeric conversions.
OPERATION is one of LOCK_SH, LOCK_EX, or LOCK_UN, possibly combined with
LOCK_NB. These constants are traditionally valued 1, 2, 8 and 4, but
-you can use the symbolic names if import them from the Fcntl module,
+you can use the symbolic names if you import them from the Fcntl module,
either individually, or as a group using the ':flock' tag. LOCK_SH
requests a shared lock, LOCK_EX requests an exclusive lock, and LOCK_UN
-releases a previously requested lock. If LOCK_NB is added to LOCK_SH or
-LOCK_EX then C<flock> will return immediately rather than blocking
+releases a previously requested lock. If LOCK_NB is bitwise-or'ed with
+LOCK_SH or LOCK_EX then C<flock> will return immediately rather than blocking
waiting for the lock (check the return status to see if you got it).
To avoid the possibility of miscoordination, Perl now flushes FILEHANDLE
then you create non-Y2K-compliant programs--and you wouldn't want to do
that, would you?
+The proper way to get a complete 4-digit year is simply:
+
+ $year += 1900;
+
+And to get the last two digits of the year (e.g., '01' in 2001) do:
+
+ $year = sprintf("%02d", $year % 100);
+
If EXPR is omitted, does C<gmtime(time())>.
In scalar context, returns the ctime(3) value:
goto ("FOO", "BAR", "GLARCH")[$i];
-The C<goto-&NAME> form is highly magical, and substitutes a call to the
-named subroutine for the currently running subroutine. This is used by
-C<AUTOLOAD> subroutines that wish to load another subroutine and then
-pretend that the other subroutine had been called in the first place
-(except that any modifications to C<@_> in the current subroutine are
-propagated to the other subroutine.) After the C<goto>, not even C<caller>
-will be able to tell that this routine was called first.
+The C<goto-&NAME> form is quite different from the other forms of C<goto>.
+In fact, it isn't a goto in the normal sense at all, and doesn't have
+the stigma associated with other gotos. Instead, it
+substitutes a call to the named subroutine for the currently running
+subroutine. This is used by C<AUTOLOAD> subroutines that wish to load
+another subroutine and then pretend that the other subroutine had been
+called in the first place (except that any modifications to C<@_>
+in the current subroutine are propagated to the other subroutine.)
+After the C<goto>, not even C<caller> will be able to tell that this
+routine was called first.
+
+NAME needn't be the name of a subroutine; it can be a scalar variable
+containing a code reference, or a block which evaluates to a code
+reference.
=item grep BLOCK LIST
print hex 'aF'; # same
Hex strings may only represent integers. Strings that would cause
-integer overflow trigger a mandatory error message.
+integer overflow trigger a warning.
=item import
$rec = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell);
-See L</split>.
+Beware that unlike C<split>, C<join> doesn't take a pattern as its
+first argument. Compare L</split>.
=item keys HASH
See also C<each>, C<values> and C<sort>.
-=item kill LIST
+=item kill SIGNAL, LIST
-Sends a signal to a list of processes. The first element of
-the list must be the signal to send. Returns the number of
+Sends a signal to a list of processes. Returns the number of
processes successfully signaled (which is not necessarily the
same as the number actually killed).
$cnt = kill 1, $child1, $child2;
kill 9, @goners;
-Unlike in the shell, in Perl if the I<SIGNAL> is negative, it kills
+If SIGNAL is zero, no signal is sent to the process. This is a
+useful way to check that the process is alive and hasn't changed
+its UID. See L<perlport> for notes on the portability of this
+construct.
+
+Unlike in the shell, if SIGNAL is negative, it kills
process groups instead of processes. (On System V, a negative I<PROCESS>
number will also kill process groups, but that's not portable.) That
means you usually want to use positive not negative signals. You may also
C<eval {}>, C<sub {}> or C<do {}>, and should not be used to exit
a grep() or map() operation.
+Note that a block by itself is semantically identical to a loop
+that executes once. Thus C<last> can be used to effect an early
+exit out of such a block.
+
See also L</continue> for an illustration of how C<last>, C<next>, and
C<redo> work.
then you create non-Y2K-compliant programs--and you wouldn't want to do
that, would you?
+The proper way to get a complete 4-digit year is simply:
+
+ $year += 1900;
+
+And to get the last two digits of the year (e.g., '01' in 2001) do:
+
+ $year = sprintf("%02d", $year % 100);
+
If EXPR is omitted, uses the current time (C<localtime(time)>).
In scalar context, returns the ctime(3) value:
instead a Perl builtin. Also see the C<Time::Local> module
(to convert the second, minutes, hours, ... back to seconds since the
stroke of midnight the 1st of January 1970, the value returned by
-time()), and the strftime(3) and mktime(3) function available via the
+time()), and the strftime(3) and mktime(3) functions available via the
POSIX module. To get somewhat similar but locale dependent date
strings, set up your locale environment variables appropriately
(please see L<perllocale>) and try for example:
=item mkdir FILENAME,MASK
+=item mkdir FILENAME
+
Creates the directory specified by FILENAME, with permissions
specified by MASK (as modified by C<umask>). If it succeeds it
returns true, otherwise it returns false and sets C<$!> (errno).
+If omitted, MASK defaults to 0777.
In general, it is better to create directories with permissive MASK,
and let the user modify that with their C<umask>, than it is to supply
first to get the correct constant definitions. If CMD is C<IPC_STAT>,
then ARG must be a variable which will hold the returned C<msqid_ds>
-structure. Returns like C<ioctl>: the undefined value for error, C<"0 but
-true"> for zero, or the actual return value otherwise. See also
+structure. Returns like C<ioctl>: the undefined value for error,
+C<"0 but true"> for zero, or the actual return value otherwise. See also
C<IPC::SysV> and C<IPC::Semaphore> documentation.
=item msgget KEY,FLAGS
=item my EXPR
+=item my EXPR : ATTRIBUTES
+
A C<my> declares the listed variables to be local (lexically) to the
enclosing block, file, or C<eval>. If
more than one value is listed, the list must be placed in parentheses. See
C<eval {}>, C<sub {}> or C<do {}>, and should not be used to exit
a grep() or map() operation.
+Note that a block by itself is semantically identical to a loop
+that executes once. Thus C<next> will exit such a block early.
+
See also L</continue> for an illustration of how C<last>, C<next>, and
C<redo> work.
open(FILEHANDLE, "<&=$fd")
+Note that this feature depends on the fdopen() C library function.
+On many UNIX systems, fdopen() is known to fail when file descriptors
+exceed a certain value, typically 255. If you need more file
+descriptors than that, consider rebuilding Perl to use the C<sfio>
+library.
+
If you open a pipe on the command C<'-'>, i.e., either C<'|-'> or C<'-|'>
with 2-arguments (or 1-argument) form of open(), then
there is an implicit fork done, and the return value of open is the pid
EXPR is omitted, uses C<$_>. For the reverse, see L</chr>.
See L<utf8> for more about Unicode.
+=item our EXPR
+
+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
+variable. If more than one value is listed, the list must be placed
+in parentheses. The C<our> declaration has no semantic effect unless
+"use strict vars" is in effect, in which case it lets you use the
+declared global variable without qualifying it with a package name.
+(But only within the lexical scope of the C<our> declaration. In this
+it differs from "use vars", which is package scoped.)
+
+An C<our> declaration declares a global variable that will be visible
+across its entire lexical scope, even across package boundaries. The
+package in which the variable is entered is determined at the point
+of the declaration, not at the point of use. This means the following
+behavior holds:
+
+ package Foo;
+ our $bar; # declares $Foo::bar for rest of lexical scope
+ $bar = 20;
+
+ package Bar;
+ print $bar; # prints 20
+
+Multiple C<our> declarations in the same lexical scope are allowed
+if they are in different packages. If they happened to be in the same
+package, Perl will emit warnings if you have asked for them.
+
+ use warnings;
+ package Foo;
+ our $bar; # declares $Foo::bar for rest of lexical scope
+ $bar = 20;
+
+ package Bar;
+ our $bar = 30; # declares $Bar::bar for rest of lexical scope
+ print $bar; # prints 30
+
+ our $bar; # emits warning
+
=item pack TEMPLATE,LIST
-Takes a list of values and packs it into a binary structure,
-returning the string containing the structure. The TEMPLATE is a
+Takes a LIST of values and converts it into a string using the rules
+given by the TEMPLATE. The resulting string is the concatenation of
+the converted values. Typically, each converted value looks
+like its machine-level representation. For example, on 32-bit machines
+a converted integer may be represented by a sequence of 4 bytes.
+
+The TEMPLATE is a
sequence of characters that give the order and type of values, as
follows:
A An ascii string, will be space padded.
Z A null terminated (asciz) string, will be null padded.
- b A bit string (ascending bit order, like vec()).
- B A bit string (descending bit order).
+ b A bit string (ascending bit order inside each byte, like vec()).
+ B A bit string (descending bit order inside each byte).
h A hex string (low nybble first).
H A hex string (high nybble first).
what a local C compiler calls 'long'. If you want
native-length longs, use the '!' suffix.)
- n A short in "network" (big-endian) order.
- N A long in "network" (big-endian) order.
- v A short in "VAX" (little-endian) order.
- V A long in "VAX" (little-endian) order.
+ n An unsigned short in "network" (big-endian) order.
+ N An unsigned long in "network" (big-endian) order.
+ v An unsigned short in "VAX" (little-endian) order.
+ V An unsigned long in "VAX" (little-endian) order.
(These 'shorts' and 'longs' are _exactly_ 16 bits and
_exactly_ 32 bits, respectively.)
=item *
Each letter may optionally be followed by a number giving a repeat
-count. With all types except C<"a">, C<"A">, C<"Z">, C<"b">, C<"B">, C<"h">,
-C<"H">, and C<"P"> the pack function will gobble up that many values from
+count. With all types except C<a>, C<A>, C<Z>, C<b>, C<B>, C<h>,
+C<H>, and C<P> the pack function will gobble up that many values from
the LIST. A C<*> for the repeat count means to use however many items are
-left.
+left, except for C<@>, C<x>, C<X>, where it is equivalent
+to C<0>, and C<u>, where it is equivalent to 1 (or 45, what is the
+same).
+
+When used with C<Z>, C<*> results in the addition of a trailing null
+byte (so the packed result will be one longer than the byte C<length>
+of the item).
+
+The repeat count for C<u> is interpreted as the maximal number of bytes
+to encode per line of output, with 0 and 1 replaced by 45.
=item *
-The C<"a">, C<"A">, and C<"Z"> types gobble just one value, but pack it as a
+The C<a>, C<A>, and C<Z> types gobble just one value, but pack it as a
string of length count, padding with nulls or spaces as necessary. When
-unpacking, C<"A"> strips trailing spaces and nulls, C<"Z"> strips everything
-after the first null, and C<"a"> returns data verbatim.
+unpacking, C<A> strips trailing spaces and nulls, C<Z> strips everything
+after the first null, and C<a> returns data verbatim. When packing,
+C<a>, and C<Z> are equivalent.
+
+If the value-to-pack is too long, it is truncated. If too long and an
+explicit count is provided, C<Z> packs only C<$count-1> bytes, followed
+by a null byte. Thus C<Z> always packs a trailing null byte under
+all circumstances.
=item *
-Likewise, the C<"b"> and C<"B"> fields pack a string that many bits long.
+Likewise, the C<b> and C<B> fields pack a string that many bits long.
+Each byte of the input field of pack() generates 1 bit of the result.
+Each result bit is based on the least-significant bit of the corresponding
+input byte, i.e., on C<ord($byte)%2>. In particular, bytes C<"0"> and
+C<"1"> generate bits 0 and 1, as do bytes C<"\0"> and C<"\1">.
+
+Starting from the beginning of the input string of pack(), each 8-tuple
+of bytes is converted to 1 byte of output. With format C<b>
+the first byte of the 8-tuple determines the least-significant bit of a
+byte, and with format C<B> it determines the most-significant bit of
+a byte.
+
+If the length of the input string is not exactly divisible by 8, the
+remainder is packed as if the input string were padded by null bytes
+at the end. Similarly, during unpack()ing the "extra" bits are ignored.
+
+If the input string of pack() is longer than needed, extra bytes are ignored.
+A C<*> for the repeat count of pack() means to use all the bytes of
+the input field. On unpack()ing the bits are converted to a string
+of C<"0">s and C<"1">s.
=item *
-The C<"h"> and C<"H"> fields pack a string that many nybbles (4-bit groups,
+The C<h> and C<H> fields pack a string that many nybbles (4-bit groups,
representable as hexadecimal digits, 0-9a-f) long.
+Each byte of the input field of pack() generates 4 bits of the result.
+For non-alphabetical bytes the result is based on the 4 least-significant
+bits of the input byte, i.e., on C<ord($byte)%16>. In particular,
+bytes C<"0"> and C<"1"> generate nybbles 0 and 1, as do bytes
+C<"\0"> and C<"\1">. For bytes C<"a".."f"> and C<"A".."F"> the result
+is compatible with the usual hexadecimal digits, so that C<"a"> and
+C<"A"> both generate the nybble C<0xa==10>. The result for bytes
+C<"g".."z"> and C<"G".."Z"> is not well-defined.
+
+Starting from the beginning of the input string of pack(), each pair
+of bytes is converted to 1 byte of output. With format C<h> the
+first byte of the pair determines the least-significant nybble of the
+output byte, and with format C<H> it determines the most-significant
+nybble.
+
+If the length of the input string is not even, it behaves as if padded
+by a null byte at the end. Similarly, during unpack()ing the "extra"
+nybbles are ignored.
+
+If the input string of pack() is longer than needed, extra bytes are ignored.
+A C<*> for the repeat count of pack() means to use all the bytes of
+the input field. On unpack()ing the bits are converted to a string
+of hexadecimal digits.
+
=item *
-The C<"p"> type packs a pointer to a null-terminated string. You are
+The C<p> type packs a pointer to a null-terminated string. You are
responsible for ensuring the string is not a temporary value (which can
potentially get deallocated before you get around to using the packed result).
-The C<"P"> type packs a pointer to a structure of the size indicated by the
-length. A NULL pointer is created if the corresponding value for C<"p"> or
-C<"P"> is C<undef>.
+The C<P> type packs a pointer to a structure of the size indicated by the
+length. A NULL pointer is created if the corresponding value for C<p> or
+C<P> is C<undef>, similarly for unpack().
=item *
-The C<"#"> character allows packing and unpacking of strings where the
-packed structure contains a byte count followed by the string itself.
-You write I<length-item>C<#>I<string-item>.
+The C</> template character allows packing and unpacking of strings where
+the packed structure contains a byte count followed by the string itself.
+You write I<length-item>C</>I<string-item>.
The I<length-item> can be any C<pack> template letter,
and describes how the length value is packed.
The ones likely to be of most use are integer-packing ones like
-C<"n"> (for Java strings), C<"w"> (for ASN.1 or SNMP)
-and C<"N"> (for Sun XDR).
+C<n> (for Java strings), C<w> (for ASN.1 or SNMP)
+and C<N> (for Sun XDR).
The I<string-item> must, at present, be C<"A*">, C<"a*"> or C<"Z*">.
For C<unpack> the length of the string is obtained from the I<length-item>,
but if you put in the '*' it will be ignored.
- unpack 'C#a', "\04Gurusamy"; gives 'Guru'
- unpack 'a3#A* A*', '007 Bond J '; gives (' Bond','J')
- pack 'n#a* w#a*','hello,','world'; gives "\000\006hello,\005world"
+ unpack 'C/a', "\04Gurusamy"; gives 'Guru'
+ unpack 'a3/A* A*', '007 Bond J '; gives (' Bond','J')
+ pack 'n/a* w/a*','hello,','world'; gives "\000\006hello,\005world"
The I<length-item> is not returned explicitly from C<unpack>.
-Adding a count to the I<length-item> letter
-is unlikely to do anything useful,
-unless that letter is C<"A">, C<"a"> or C<"Z">.
-Packing with a I<length-item> of C<"a"> or C<"Z">
-may introduce C<"\000"> characters,
+Adding a count to the I<length-item> letter is unlikely to do anything
+useful, unless that letter is C<A>, C<a> or C<Z>. Packing with a
+I<length-item> of C<a> or C<Z> may introduce C<"\000"> characters,
which Perl does not regard as legal in numeric strings.
=item *
-The integer types C<"s">, C<"S">, C<"l">, and C<"L"> may be
-immediately followed by a C<"!"> suffix to signify native shorts or
-longs--as you can see from above for example a bare C<"l"> does mean
+The integer types C<s>, C<S>, C<l>, and C<L> may be
+immediately followed by a C<!> suffix to signify native shorts or
+longs--as you can see from above for example a bare C<l> does mean
exactly 32 bits, the native C<long> (as seen by the local C compiler)
may be larger. This is an issue mainly in 64-bit platforms. You can
-see whether using C<"!"> makes any difference by
+see whether using C<!> makes any difference by
print length(pack("s")), " ", length(pack("s!")), "\n";
print length(pack("l")), " ", length(pack("l!")), "\n";
-C<"i!"> and C<"I!"> also work but only because of completeness;
-they are identical to C<"i"> and C<"I">.
+C<i!> and C<I!> also work but only because of completeness;
+they are identical to C<i> and C<I>.
The actual sizes (in bytes) of native shorts, ints, longs, and long
longs on the platform where Perl was built are also available via
print $Config{longsize}, "\n";
print $Config{longlongsize}, "\n";
-(The C<$Config{longlongsize}> will be empty if your system does
+(The C<$Config{longlongsize}> will be undefine if your system does
not support long longs.)
=item *
-The integer formats C<"s">, C<"S">, C<"i">, C<"I">, C<"l">, and C<"L">
+The integer formats C<s>, C<S>, C<i>, C<I>, C<l>, and C<L>
are inherently non-portable between processors and operating systems
because they obey the native byteorder and endianness. For example a
-4-byte integer 0x87654321 (2271560481 decimal) be ordered natively
+4-byte integer 0x12345678 (305419896 decimal) be ordered natively
(arranged in and handled by the CPU registers) into bytes as
0x12 0x34 0x56 0x78 # little-endian
0x78 0x56 0x34 0x12 # big-endian
-Basically, the Intel, Alpha, and VAX CPUs and little-endian, while
+Basically, the Intel, Alpha, and VAX CPUs are little-endian, while
everybody else, for example Motorola m68k/88k, PPC, Sparc, HP PA,
Power, and Cray are big-endian. MIPS can be either: Digital used it
in little-endian mode; SGI uses it in big-endian mode.
Plea for Peace" by Danny Cohen, USC/ISI IEN 137, April 1, 1980) and
the egg-eating habits of the Lilliputians.
-Some systems may even have weird byte orders such as
+Some systems may have even weirder byte orders such as
0x56 0x78 0x12 0x34
0x34 0x12 0x78 0x56
Byteorders C<'1234'> and C<'12345678'> are little-endian, C<'4321'>
and C<'87654321'> are big-endian.
-If you want portable packed integers use the formats C<"n">, C<"N">,
-C<"v">, and C<"V">, their byte endianness and size is known.
+If you want portable packed integers use the formats C<n>, C<N>,
+C<v>, and C<V>, their byte endianness and size is known.
See also L<perlport>.
=item *
C<pack> (and C<unpack>) handle their output and input as flat
sequences of bytes.
+=item *
+
+A comment in a TEMPLATE starts with C<#> and goes to the end of line.
+
+=item *
+
+If TEMPLATE requires more arguments to pack() than actually given, pack()
+assumes additional C<""> arguments. If TEMPLATE requires less arguments
+to pack() than actually given, extra arguments are ignored.
+
=back
Examples:
=item recv SOCKET,SCALAR,LENGTH,FLAGS
Receives a message on a socket. Attempts to receive LENGTH bytes of
-data into variable SCALAR from the specified SOCKET filehandle.
-Actually does a C C<recvfrom>, so that it can return the address of the
-sender. Returns the undefined value if there's an error. SCALAR will
-be grown or shrunk to the length actually read. Takes the same flags
-as the system call of the same name.
-See L<perlipc/"UDP: Message Passing"> for examples.
+data into variable SCALAR from the specified SOCKET filehandle. SCALAR
+will be grown or shrunk to the length actually read. Takes the same
+flags as the system call of the same name. Returns the address of the
+sender if SOCKET's protocol supports this; returns an empty string
+otherwise. If there's an error, returns the undefined value. This call
+is actually implemented in terms of recvfrom(2) system call. See
+L<perlipc/"UDP: Message Passing"> for examples.
=item redo LABEL
C<eval {}>, C<sub {}> or C<do {}>, and should not be used to exit
a grep() or map() operation.
+Note that a block by itself is semantically identical to a loop
+that executes once. Thus C<redo> inside such a block will effectively
+turn it into a looping construct.
+
See also L</continue> for an illustration of how C<last>, C<next>, and
C<redo> work.
open files, or pre-existing files. Check L<perlport> and either the
rename(2) manpage or equivalent system documentation for details.
+=item require VERSION
+
=item require EXPR
=item require
Demands some semantics specified by EXPR, or by C<$_> if EXPR is not
-supplied. If EXPR is numeric, demands that the current version of Perl
-(C<$]> or $PERL_VERSION) be equal or greater than EXPR.
+supplied.
+
+If a VERSION is specified as a literal of the form v5.6.1,
+demands that the current version of Perl (C<$^V> or $PERL_VERSION) be
+at least as recent as that version, at run time. (For compatibility
+with older versions of Perl, a numeric argument will also be interpreted
+as VERSION.) Compare with L</use>, which can do a similar check at
+compile time.
+
+ require v5.6.1; # run time version check
+ require 5.6.1; # ditto
+ require 5.005_03; # float version allowed for compatibility
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
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;
- $INC{$filename} = $realfilename;
return $result;
}
POSITION, C<1> to set it to the current position plus POSITION, and
C<2> to set it to EOF plus POSITION (typically negative). For WHENCE
you may use the constants C<SEEK_SET>, C<SEEK_CUR>, and C<SEEK_END>
-(start of the file, current position, end of the file) from any of the
-modules Fcntl, C<IO::Seekable>, or POSIX. Returns C<1> upon success,
-C<0> otherwise.
+(start of the file, current position, end of the file) from the Fcntl
+module. Returns C<1> upon success, C<0> otherwise.
If you want to position file for C<sysread> or C<syswrite>, don't use
C<seek>--buffering makes its effect on the file's system position
Sets the current process group for the specified PID, C<0> for the current
process. Will produce a fatal error if used on a machine that doesn't
-implement setpgrp(2). If the arguments are omitted, it defaults to
-C<0,0>. Note that the POSIX version of C<setpgrp> does not accept any
-arguments, so only C<setpgrp(0,0)> is portable. See also C<POSIX::setsid()>.
+implement POSIX setpgid(2) or BSD setpgrp(2). If the arguments are omitted,
+it defaults to C<0,0>. Note that the BSD 4.2 version of C<setpgrp> does not
+accept any arguments, so only C<setpgrp(0,0)> is portable. See also
+C<POSIX::setsid()>.
=item setpriority WHICH,WHO,PRIORITY
array, returns the undefined value. If ARRAY is omitted, shifts the
C<@_> array within the lexical scope of subroutines and formats, and the
C<@ARGV> array at file scopes or within the lexical scopes established by
-the C<eval ''>, C<BEGIN {}>, C<END {}>, and C<INIT {}> constructs.
+the C<eval ''>, C<BEGIN {}>, C<INIT {}>, C<CHECK {}>, and C<END {}>
+constructs.
+
See also C<unshift>, C<push>, and C<pop>. C<Shift()> and C<unshift> do the
same thing to the left end of an array that C<pop> and C<push> do to the
right end.
Returns the sine of EXPR (expressed in radians). If EXPR is omitted,
returns sine of C<$_>.
-For the inverse sine operation, you may use the C<POSIX::asin>
+For the inverse sine operation, you may use the C<Math::Trig::asin>
function, or use this relation:
sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) }
to get the proper definitions imported. See the examples in
L<perlipc/"Sockets: Client/Server Communication">.
+On systems that support a close-on-exec flag on files, the flag will
+be set for the newly opened file descriptor, as determined by the
+value of $^F. See L<perlvar/$^F>.
+
=item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
Creates an unnamed pair of sockets in the specified domain, of the
for the system call of the same name. If unimplemented, yields a fatal
error. Returns true if successful.
+On systems that support a close-on-exec flag on files, the flag will
+be set for the newly opened file descriptors, as determined by the value
+of $^F. See L<perlvar/$^F>.
+
Some systems defined C<pipe> in terms of C<socketpair>, in which a call
to C<pipe(Rdr, Wtr)> is essentially:
of a SUBNAME, you can provide a BLOCK as an anonymous, in-line sort
subroutine.
-In the interests of efficiency the normal calling code for subroutines is
-bypassed, with the following effects: the subroutine may not be a
-recursive subroutine, and the two elements to be compared are passed into
-the subroutine not via C<@_> but as the package global variables $a and
-$b (see example below). They are passed by reference, so don't
-modify $a and $b. And don't try to declare them as lexicals either.
+If the subroutine's prototype is C<($$)>, the elements to be compared
+are passed by reference in C<@_>, as for a normal subroutine. If not,
+the normal calling code for subroutines is bypassed in the interests of
+efficiency, and the elements to be compared are passed into the subroutine
+as the package global variables $a and $b (see example below). Note that
+in the latter case, it is usually counter-productive to declare $a and
+$b as lexicals.
+
+In either case, the subroutine may not be recursive. The values to be
+compared are always passed by reference, so don't modify them.
You also cannot exit out of the sort block or subroutine using any of the
loop control operators described in L<perlsyn> or with C<goto>.
||
$a->[2] cmp $b->[2]
} map { [$_, /=(\d+)/, uc($_)] } @old;
+
+ # using a prototype allows you to use any comparison subroutine
+ # as a sort subroutine (including other package's subroutines)
+ package other;
+ sub backwards ($$) { $_[1] cmp $_[0]; } # $a and $b are not set here
+
+ package main;
+ @new = sort other::backwards @old;
If you're using strict, you I<must not> declare $a
and $b as lexicals. They are package globals. That means
=item splice ARRAY,OFFSET
+=item splice ARRAY
+
Removes the elements designated by OFFSET and LENGTH from an array, and
replaces them with the elements of LIST, if any. In list context,
returns the elements removed from the array. In scalar context,
removed. The array grows or shrinks as necessary.
If OFFSET is negative then it starts that far from the end of the array.
If LENGTH is omitted, removes everything from OFFSET onward.
-If LENGTH is negative, leave that many elements off the end of the array.
+If LENGTH is negative, leaves that many elements off the end of the array.
+If both OFFSET and LENGTH are omitted, removes everything.
+
The following equivalences hold (assuming C<$[ == 0>):
push(@a,$x,$y) splice(@a,@a,0,$x,$y)
for integer
l interpret integer as C type "long" or "unsigned long"
h interpret integer as C type "short" or "unsigned short"
+ If no flags, interpret integer as C type "int" or "unsigned"
-There is also one Perl-specific flag:
+There are also two Perl-specific flags:
V interpret integer as Perl's standard integer type
+ v interpret string as a vector of integers, output as
+ numbers separated either by dots, or by an arbitrary
+ string received from the argument list when the flag
+ is preceded by C<*>
Where a number would appear in the flags, an asterisk (C<*>) may be
used instead, in which case Perl uses the next item in the parameter
If a field width obtained through C<*> is negative, it has the same
effect as the C<-> flag: left-justification.
+The C<v> flag is useful for displaying ordinal values of characters
+in arbitrary strings:
+
+ printf "version is v%vd\n", $^V; # Perl's version
+ printf "address is %*vX\n", ":", $addr; # IPv6 address
+ printf "bits are %*vb\n", " ", $bits; # random bitstring
+
If C<use locale> is in effect, the character used for the decimal
point in formatted real numbers is affected by the LC_NUMERIC locale.
See L<perllocale>.
If Perl understands "quads" (64-bit integers) (this requires
-either that the platform natively supports quads or that Perl
-has been specifically compiled to support quads), the flags
+either that the platform natively support quads or that Perl
+be specifically compiled to support quads), the characters
d u o x X b i D U O
print "quads\n";
If Perl understands "long doubles" (this requires that the platform
-supports long doubles), the flags
+support long doubles), the flags
e f g E F G
5 gid numeric group ID of file's owner
6 rdev the device identifier (special files only)
7 size total size of file, in bytes
- 8 atime last access time since the epoch
- 9 mtime last modify time since the epoch
- 10 ctime inode change time (NOT creation time!) since the epoch
+ 8 atime last access time in seconds since the epoch
+ 9 mtime last modify time in seconds since the epoch
+ 10 ctime inode change time (NOT creation time!) in seconds since the epoch
11 blksize preferred block size for file system I/O
12 blocks actual number of blocks allocated
print "$file is executable NFS file\n";
}
-(This works on machines only for which the device number is negative under NFS.)
+(This works on machines only for which the device number is negative
+under NFS.)
Because the mode contains both the file type and its permissions, you
should mask off the file type portion and (s)printf using a C<"%o">
$filename, $sb->size, $sb->mode & 07777,
scalar localtime $sb->mtime;
+You can import symbolic mode constants (C<S_IF*>) and functions
+(C<S_IS*>) from the Fcntl module:
+
+ use Fcntl ':mode';
+
+ $mode = (stat($filename))[2];
+
+ $user_rwx = ($mode & S_IRWXU) >> 6;
+ $group_read = ($mode & S_IRGRP) >> 3;
+ $other_execute = $mode & S_IXOTH;
+
+ printf "Permissions are %04o\n", S_ISMODE($mode), "\n";
+
+ $is_setuid = $mode & S_ISUID;
+ $is_setgid = S_ISDIR($mode);
+
+You could write the last two using the C<-u> and C<-d> operators.
+The commonly available S_IF* constants are
+
+ # Permissions: read, write, execute, for user, group, others.
+
+ S_IRWXU S_IRUSR S_IWUSR S_IXUSR
+ S_IRWXG S_IRGRP S_IWGRP S_IXGRP
+ S_IRWXO S_IROTH S_IWOTH S_IXOTH
+
+ # Setuid/Setgid/Stickiness.
+
+ S_ISUID S_ISGID S_ISVTX S_ISTXT
+
+ # File types. Not necessarily all are available on your system.
+
+ S_IFREG S_IFDIR S_IFLNK S_IFBLK S_ISCHR S_IFIFO S_IFSOCK S_IFWHT S_ENFMT
+
+ # The following are compatibility aliases for S_IRUSR, S_IWUSR, S_IXUSR.
+
+ S_IREAD S_IWRITE S_IEXEC
+
+and the S_IF* functions are
+
+ S_IFMODE($mode) the part of $mode containg the permission bits
+ and the setuid/setgid/sticky bits
+
+ S_IFMT($mode) the part of $mode containing the file type
+ which can be bit-anded with e.g. S_IFREG
+ or with the following functions
+
+ # The operators -f, -d, -l, -b, -c, -p, and -s.
+
+ S_ISREG($mode) S_ISDIR($mode) S_ISLNK($mode)
+ S_ISBLK($mode) S_ISCHR($mode) S_ISFIFO($mode) S_ISSOCK($mode)
+
+ # No direct -X operator counterpart, but for the first one
+ # the -g operator is often equivalent. The ENFMT stands for
+ # record flocking enforcement, a platform-dependent feature.
+
+ S_ISENFMT($mode) S_ISWHT($mode)
+
+See your native chmod(2) and stat(2) documentation for more details
+about the S_* constants.
+
=item study SCALAR
=item study
print;
}
-In searching for C</\bfoo\b/>, only those locations in C<$_> that contain C<"f">
-will be looked at, because C<"f"> is rarer than C<"o">. In general, this is
+In searching for C</\bfoo\b/>, only those locations in C<$_> that contain C<f>
+will be looked at, because C<f> is rarer than C<o>. In general, this is
a big win except in pathological cases. The only question is whether
it saves you more time than it took to build the linked list in the
first place.
=item sub NAME BLOCK
This is subroutine definition, not a real function I<per se>. With just a
-NAME (and possibly prototypes), it's just a forward declaration. Without
-a NAME, it's an anonymous function declaration, and does actually return a
-value: the CODE ref of the closure you just created. See L<perlsub> and
-L<perlref> for details.
+NAME (and possibly prototypes or attributes), it's just a forward declaration.
+Without a NAME, it's an anonymous function declaration, and does actually
+return a value: the CODE ref of the closure you just created. See L<perlsub>
+and L<perlref> for details.
=item substr EXPR,OFFSET,LENGTH,REPLACEMENT
supported by perl: zero means read-only, one means write-only, and two
means read/write. We know that these values do I<not> work under
OS/390 & VM/ESA Unix and on the Macintosh; you probably don't want to
-se them in new code, use thhe constants discussed in the preceding
-paragraph.
+use them in new code.
If the file named by FILENAME does not exist and the C<open> call creates
it (typically because MODE includes the C<O_CREAT> flag), then the value of
Better to omit it. See the perlfunc(1) entry on C<umask> for more
on this.
+Note that C<sysopen> depends on the fdopen() C library function.
+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<sfio>
+library, or perhaps using the POSIX::open() function.
+
See L<perlopentut> for a kinder, gentler explanation of opening files.
=item sysread FILEHANDLE,SCALAR,LENGTH,OFFSET
and C<2> to set it to EOF plus POSITION (typically negative). For
WHENCE, you may also use the constants C<SEEK_SET>, C<SEEK_CUR>, and
C<SEEK_END> (start of the file, current position, end of the file)
-from any of the modules Fcntl, C<IO::Seekable>, or POSIX.
+from the Fcntl module.
Returns the new position, or the undefined value on failure. A position
of zero is returned as the string C<"0 but true">; thus C<sysseek> returns
=item unpack TEMPLATE,EXPR
C<unpack> does the reverse of C<pack>: it takes a string
-representing a structure and expands it out into a list of values.
+and expands it out into a list of values.
(In scalar context, it returns merely the first value produced.)
+
+The string is broken into chunks described by the TEMPLATE. Each chunk
+is converted separately to a value. Typically, either the string is a result
+of C<pack>, or the bytes of the string represent a C structure of some
+kind.
+
The TEMPLATE has the same format as in the C<pack> function.
Here's a subroutine that does substring:
sub ordinal { unpack("c",$_[0]); } # same as ord()
-In addition, you may prefix a field with a %E<lt>numberE<gt> to indicate that
+In addition to fields allowed in pack(), you may prefix a field with
+a %E<lt>numberE<gt> to indicate that
you want a E<lt>numberE<gt>-bit checksum of the items instead of the items
-themselves. Default is a 16-bit checksum. For example, the following
+themselves. Default is a 16-bit checksum. Checksum is calculated by
+summing numeric values of expanded values (for string fields the sum of
+C<ord($char)> is taken, for bit fields the sum of zeroes and ones).
+
+For example, the following
computes the same number as the System V sum program:
$checksum = do {
$setbits = unpack("%32b*", $selectmask);
-The C<"p"> and C<"P"> formats should be used with care. Since Perl
+The C<p> and C<P> formats should be used with care. Since Perl
has no way of checking whether the value passed to C<unpack()>
corresponds to a valid memory location, passing a pointer value that's
not known to be valid is likely to have disastrous consequences.
+If the repeat count of a field is larger than what the remainder of
+the input string allows, repeat count is decreased. If the input string
+is longer than one described by the TEMPLATE, the rest is ignored.
+
See L</pack> for more examples and notes.
=item untie VARIABLE
prepended elements stay in the same order. Use C<reverse> to do the
reverse.
+=item use Module VERSION LIST
+
+=item use Module VERSION
+
=item use Module LIST
=item use Module
-=item use Module VERSION LIST
-
=item use VERSION
Imports some semantics into the current package from the named module,
except that Module I<must> be a bareword.
-If the first argument to C<use> is a number, it is treated as a version
-number instead of a module name. If the version of the Perl interpreter
-is less than VERSION, then an error message is printed and Perl exits
-immediately. This is often useful if you need to check the current
-Perl version before C<use>ing library modules that have changed in
-incompatible ways from older versions of Perl. (We try not to do
-this more than we have to.)
+VERSION, which can be specified as a literal of the form v5.6.1, demands
+that the current version of Perl (C<$^V> or $PERL_VERSION) be at least
+as recent as that version. (For compatibility with older versions of Perl,
+a numeric literal will also be interpreted as VERSION.) If the version
+of the running Perl interpreter is less than VERSION, then an error
+message is printed and Perl exits immediately without attempting to
+parse the rest of the file. Compare with L</require>, which can do a
+similar check at run time.
+
+ use v5.6.1; # compile time version check
+ use 5.6.1; # ditto
+ use 5.005_03; # float version allowed for compatibility
+
+This is often useful if you need to check the current Perl version before
+C<use>ing library modules that have changed in incompatible ways from
+older versions of Perl. (We try not to do this more than we have to.)
The C<BEGIN> forces the C<require> and C<import> to happen at compile time. The
C<require> makes sure the module is loaded into memory if it hasn't been
C<import> method any way it likes, though most modules just choose to
derive their C<import> method via inheritance from the C<Exporter> class that
is defined in the C<Exporter> module. See L<Exporter>. If no C<import>
-method can be found then the error is currently silently ignored. This
-may change to a fatal error in a future version.
+method can be found then the call is skipped.
If you don't want your namespace altered, explicitly supply an empty list:
If the VERSION argument is present between Module and LIST, then the
C<use> will call the VERSION method in class Module with the given
version as an argument. The default VERSION method, inherited from
-the Universal class, croaks if the given version is larger than the
-value of the variable C<$Module::VERSION>. (Note that there is not a
-comma after VERSION!)
+the UNIVERSAL class, croaks if the given version is larger than the
+value of the variable C<$Module::VERSION>.
+
+Again, there is a distinction between omitting LIST (C<import> called
+with no arguments) and an explicit empty LIST C<()> (C<import> not
+called). Note that there is no comma after VERSION!
Because this is a wide-open interface, pragmas (compiler directives)
are also implemented this way. Currently implemented pragmas are:
use integer;
use diagnostics;
- use sigtrap qw(SEGV BUS);
- use strict qw(subs vars refs);
- use subs qw(afunc blurfl);
- use warning qw(all);
+ use sigtrap qw(SEGV BUS);
+ use strict qw(subs vars refs);
+ use subs qw(afunc blurfl);
+ use warnings qw(all);
Some of these pseudo-modules import semantics into the current
block scope (like C<strict> or C<integer>, unlike ordinary modules,
no integer;
no strict 'refs';
- no warning;
+ no warnings;
If no C<unimport> method can be found the call fails with a fatal error.
=item vec EXPR,OFFSET,BITS
-Treats the string in EXPR as a vector of unsigned integers, and
-returns the value of the bit field specified by OFFSET. BITS
-specifies the number of bits that are reserved for each entry in the
-bit vector. This must be a power of two from 1 to 32 (or 64, if your
-platform supports that).
+Treats the string in EXPR as a bit vector made up of elements of
+width BITS, and returns the value of the element specified by OFFSET
+as an unsigned integer. BITS therefore specifies the number of bits
+that are reserved for each element in the bit vector. This must
+be a power of two from 1 to 32 (or 64, if your platform supports
+that).
+
+If BITS is 8, "elements" coincide with bytes of the input string.
+
+If BITS is 16 or more, bytes of the input string are grouped into chunks
+of size BITS/8, and each group is converted to a number as with
+pack()/unpack() with big-endian formats C<n>/C<N> (and analoguously
+for BITS==64). See L<"pack"> for details.
+
+If bits is 4 or less, the string is broken into bytes, then the bits
+of each byte are broken into 8/BITS groups. Bits of a byte are
+numbered in a little-endian-ish way, as in C<0x01>, C<0x02>,
+C<0x04>, C<0x08>, C<0x10>, C<0x20>, C<0x40>, C<0x80>. For example,
+breaking the single input byte C<chr(0x36)> into two groups gives a list
+C<(0x6, 0x3)>; breaking it into 4 groups gives C<(0x2, 0x1, 0x3, 0x0)>.
C<vec> may also be assigned to, in which case parentheses are needed
to give the expression the correct precedence as in
vec($image, $max_x * $x + $y, 8) = 3;
-Vectors created with C<vec> can also be manipulated with the logical
-operators C<|>, C<&>, and C<^>, which will assume a bit vector
-operation is desired when both operands are strings.
+If the selected element is off the end of the string, the value 0 is
+returned. If an element off the end of the string is written to,
+Perl will first extend the string with sufficiently many zero bytes.
+
+Strings created with C<vec> can also be manipulated with the logical
+operators C<|>, C<&>, C<^>, and C<~>. These operators will assume a bit
+vector operation is desired when both operands are strings.
See L<perlop/"Bitwise String Operators">.
The following code will build up an ASCII string saying C<'PerlPerlPerl'>.
my $foo = '';
vec($foo, 0, 32) = 0x5065726C; # 'Perl'
+
+ # $foo eq "Perl" eq "\x50\x65\x72\x6C", 32 bits
+ print vec($foo, 0, 8); # prints 80 == 0x50 == ord('P')
+
vec($foo, 2, 16) = 0x5065; # 'PerlPe'
vec($foo, 3, 16) = 0x726C; # 'PerlPerl'
vec($foo, 8, 8) = 0x50; # 'PerlPerlP'
If you know the exact length in bits, it can be used in place of the C<*>.
+Here is an example to illustrate how the bits actually fall in place:
+
+ #!/usr/bin/perl -wl
+
+ print <<'EOT';
+ 0 1 2 3
+ unpack("V",$_) 01234567890123456789012345678901
+ ------------------------------------------------------------------
+ EOT
+
+ for $w (0..3) {
+ $width = 2**$w;
+ for ($shift=0; $shift < $width; ++$shift) {
+ for ($off=0; $off < 32/$width; ++$off) {
+ $str = pack("B*", "0"x32);
+ $bits = (1<<$shift);
+ vec($str, $off, $width) = $bits;
+ $res = unpack("b*",$str);
+ $val = unpack("V", $str);
+ write;
+ }
+ }
+ }
+
+ format STDOUT =
+ vec($_,@#,@#) = @<< == @######### @>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
+ $off, $width, $bits, $val, $res
+ .
+ __END__
+
+Regardless of the machine architecture on which it is run, the above
+example should print the following table:
+
+ 0 1 2 3
+ unpack("V",$_) 01234567890123456789012345678901
+ ------------------------------------------------------------------
+ vec($_, 0, 1) = 1 == 1 10000000000000000000000000000000
+ vec($_, 1, 1) = 1 == 2 01000000000000000000000000000000
+ vec($_, 2, 1) = 1 == 4 00100000000000000000000000000000
+ vec($_, 3, 1) = 1 == 8 00010000000000000000000000000000
+ vec($_, 4, 1) = 1 == 16 00001000000000000000000000000000
+ vec($_, 5, 1) = 1 == 32 00000100000000000000000000000000
+ vec($_, 6, 1) = 1 == 64 00000010000000000000000000000000
+ vec($_, 7, 1) = 1 == 128 00000001000000000000000000000000
+ vec($_, 8, 1) = 1 == 256 00000000100000000000000000000000
+ vec($_, 9, 1) = 1 == 512 00000000010000000000000000000000
+ vec($_,10, 1) = 1 == 1024 00000000001000000000000000000000
+ vec($_,11, 1) = 1 == 2048 00000000000100000000000000000000
+ vec($_,12, 1) = 1 == 4096 00000000000010000000000000000000
+ vec($_,13, 1) = 1 == 8192 00000000000001000000000000000000
+ vec($_,14, 1) = 1 == 16384 00000000000000100000000000000000
+ vec($_,15, 1) = 1 == 32768 00000000000000010000000000000000
+ vec($_,16, 1) = 1 == 65536 00000000000000001000000000000000
+ vec($_,17, 1) = 1 == 131072 00000000000000000100000000000000
+ vec($_,18, 1) = 1 == 262144 00000000000000000010000000000000
+ vec($_,19, 1) = 1 == 524288 00000000000000000001000000000000
+ vec($_,20, 1) = 1 == 1048576 00000000000000000000100000000000
+ vec($_,21, 1) = 1 == 2097152 00000000000000000000010000000000
+ vec($_,22, 1) = 1 == 4194304 00000000000000000000001000000000
+ vec($_,23, 1) = 1 == 8388608 00000000000000000000000100000000
+ vec($_,24, 1) = 1 == 16777216 00000000000000000000000010000000
+ vec($_,25, 1) = 1 == 33554432 00000000000000000000000001000000
+ vec($_,26, 1) = 1 == 67108864 00000000000000000000000000100000
+ vec($_,27, 1) = 1 == 134217728 00000000000000000000000000010000
+ vec($_,28, 1) = 1 == 268435456 00000000000000000000000000001000
+ vec($_,29, 1) = 1 == 536870912 00000000000000000000000000000100
+ vec($_,30, 1) = 1 == 1073741824 00000000000000000000000000000010
+ vec($_,31, 1) = 1 == 2147483648 00000000000000000000000000000001
+ vec($_, 0, 2) = 1 == 1 10000000000000000000000000000000
+ vec($_, 1, 2) = 1 == 4 00100000000000000000000000000000
+ vec($_, 2, 2) = 1 == 16 00001000000000000000000000000000
+ vec($_, 3, 2) = 1 == 64 00000010000000000000000000000000
+ vec($_, 4, 2) = 1 == 256 00000000100000000000000000000000
+ vec($_, 5, 2) = 1 == 1024 00000000001000000000000000000000
+ vec($_, 6, 2) = 1 == 4096 00000000000010000000000000000000
+ vec($_, 7, 2) = 1 == 16384 00000000000000100000000000000000
+ vec($_, 8, 2) = 1 == 65536 00000000000000001000000000000000
+ vec($_, 9, 2) = 1 == 262144 00000000000000000010000000000000
+ vec($_,10, 2) = 1 == 1048576 00000000000000000000100000000000
+ vec($_,11, 2) = 1 == 4194304 00000000000000000000001000000000
+ vec($_,12, 2) = 1 == 16777216 00000000000000000000000010000000
+ vec($_,13, 2) = 1 == 67108864 00000000000000000000000000100000
+ vec($_,14, 2) = 1 == 268435456 00000000000000000000000000001000
+ vec($_,15, 2) = 1 == 1073741824 00000000000000000000000000000010
+ vec($_, 0, 2) = 2 == 2 01000000000000000000000000000000
+ vec($_, 1, 2) = 2 == 8 00010000000000000000000000000000
+ vec($_, 2, 2) = 2 == 32 00000100000000000000000000000000
+ vec($_, 3, 2) = 2 == 128 00000001000000000000000000000000
+ vec($_, 4, 2) = 2 == 512 00000000010000000000000000000000
+ vec($_, 5, 2) = 2 == 2048 00000000000100000000000000000000
+ vec($_, 6, 2) = 2 == 8192 00000000000001000000000000000000
+ vec($_, 7, 2) = 2 == 32768 00000000000000010000000000000000
+ vec($_, 8, 2) = 2 == 131072 00000000000000000100000000000000
+ vec($_, 9, 2) = 2 == 524288 00000000000000000001000000000000
+ vec($_,10, 2) = 2 == 2097152 00000000000000000000010000000000
+ vec($_,11, 2) = 2 == 8388608 00000000000000000000000100000000
+ vec($_,12, 2) = 2 == 33554432 00000000000000000000000001000000
+ vec($_,13, 2) = 2 == 134217728 00000000000000000000000000010000
+ vec($_,14, 2) = 2 == 536870912 00000000000000000000000000000100
+ vec($_,15, 2) = 2 == 2147483648 00000000000000000000000000000001
+ vec($_, 0, 4) = 1 == 1 10000000000000000000000000000000
+ vec($_, 1, 4) = 1 == 16 00001000000000000000000000000000
+ vec($_, 2, 4) = 1 == 256 00000000100000000000000000000000
+ vec($_, 3, 4) = 1 == 4096 00000000000010000000000000000000
+ vec($_, 4, 4) = 1 == 65536 00000000000000001000000000000000
+ vec($_, 5, 4) = 1 == 1048576 00000000000000000000100000000000
+ vec($_, 6, 4) = 1 == 16777216 00000000000000000000000010000000
+ vec($_, 7, 4) = 1 == 268435456 00000000000000000000000000001000
+ vec($_, 0, 4) = 2 == 2 01000000000000000000000000000000
+ vec($_, 1, 4) = 2 == 32 00000100000000000000000000000000
+ vec($_, 2, 4) = 2 == 512 00000000010000000000000000000000
+ vec($_, 3, 4) = 2 == 8192 00000000000001000000000000000000
+ vec($_, 4, 4) = 2 == 131072 00000000000000000100000000000000
+ vec($_, 5, 4) = 2 == 2097152 00000000000000000000010000000000
+ vec($_, 6, 4) = 2 == 33554432 00000000000000000000000001000000
+ vec($_, 7, 4) = 2 == 536870912 00000000000000000000000000000100
+ vec($_, 0, 4) = 4 == 4 00100000000000000000000000000000
+ vec($_, 1, 4) = 4 == 64 00000010000000000000000000000000
+ vec($_, 2, 4) = 4 == 1024 00000000001000000000000000000000
+ vec($_, 3, 4) = 4 == 16384 00000000000000100000000000000000
+ vec($_, 4, 4) = 4 == 262144 00000000000000000010000000000000
+ vec($_, 5, 4) = 4 == 4194304 00000000000000000000001000000000
+ vec($_, 6, 4) = 4 == 67108864 00000000000000000000000000100000
+ vec($_, 7, 4) = 4 == 1073741824 00000000000000000000000000000010
+ vec($_, 0, 4) = 8 == 8 00010000000000000000000000000000
+ vec($_, 1, 4) = 8 == 128 00000001000000000000000000000000
+ vec($_, 2, 4) = 8 == 2048 00000000000100000000000000000000
+ vec($_, 3, 4) = 8 == 32768 00000000000000010000000000000000
+ vec($_, 4, 4) = 8 == 524288 00000000000000000001000000000000
+ vec($_, 5, 4) = 8 == 8388608 00000000000000000000000100000000
+ vec($_, 6, 4) = 8 == 134217728 00000000000000000000000000010000
+ vec($_, 7, 4) = 8 == 2147483648 00000000000000000000000000000001
+ vec($_, 0, 8) = 1 == 1 10000000000000000000000000000000
+ vec($_, 1, 8) = 1 == 256 00000000100000000000000000000000
+ vec($_, 2, 8) = 1 == 65536 00000000000000001000000000000000
+ vec($_, 3, 8) = 1 == 16777216 00000000000000000000000010000000
+ vec($_, 0, 8) = 2 == 2 01000000000000000000000000000000
+ vec($_, 1, 8) = 2 == 512 00000000010000000000000000000000
+ vec($_, 2, 8) = 2 == 131072 00000000000000000100000000000000
+ vec($_, 3, 8) = 2 == 33554432 00000000000000000000000001000000
+ vec($_, 0, 8) = 4 == 4 00100000000000000000000000000000
+ vec($_, 1, 8) = 4 == 1024 00000000001000000000000000000000
+ vec($_, 2, 8) = 4 == 262144 00000000000000000010000000000000
+ vec($_, 3, 8) = 4 == 67108864 00000000000000000000000000100000
+ vec($_, 0, 8) = 8 == 8 00010000000000000000000000000000
+ vec($_, 1, 8) = 8 == 2048 00000000000100000000000000000000
+ vec($_, 2, 8) = 8 == 524288 00000000000000000001000000000000
+ vec($_, 3, 8) = 8 == 134217728 00000000000000000000000000010000
+ vec($_, 0, 8) = 16 == 16 00001000000000000000000000000000
+ vec($_, 1, 8) = 16 == 4096 00000000000010000000000000000000
+ vec($_, 2, 8) = 16 == 1048576 00000000000000000000100000000000
+ vec($_, 3, 8) = 16 == 268435456 00000000000000000000000000001000
+ vec($_, 0, 8) = 32 == 32 00000100000000000000000000000000
+ vec($_, 1, 8) = 32 == 8192 00000000000001000000000000000000
+ vec($_, 2, 8) = 32 == 2097152 00000000000000000000010000000000
+ vec($_, 3, 8) = 32 == 536870912 00000000000000000000000000000100
+ vec($_, 0, 8) = 64 == 64 00000010000000000000000000000000
+ vec($_, 1, 8) = 64 == 16384 00000000000000100000000000000000
+ vec($_, 2, 8) = 64 == 4194304 00000000000000000000001000000000
+ vec($_, 3, 8) = 64 == 1073741824 00000000000000000000000000000010
+ vec($_, 0, 8) = 128 == 128 00000001000000000000000000000000
+ vec($_, 1, 8) = 128 == 32768 00000000000000010000000000000000
+ vec($_, 2, 8) = 128 == 8388608 00000000000000000000000100000000
+ vec($_, 3, 8) = 128 == 2147483648 00000000000000000000000000000001
+
=item wait
Behaves like the wait(2) system call on your system: it waits for a child
projects / p5sagit/p5-mst-13.2.git / blobdiff