=item chdir EXPR
+=item chdir FILEHANDLE
+
+=item chdir DIRHANDLE
+
+=item chdir
+
Changes the working directory to EXPR, if possible. If EXPR is omitted,
changes to the directory specified by C<$ENV{HOME}>, if set; if not,
changes to the directory specified by C<$ENV{LOGDIR}>. (Under VMS, the
neither is set, C<chdir> does nothing. It returns true upon success,
false otherwise. See the example under C<die>.
+On systems that support fchdir, you might pass a file handle or
+directory handle as argument. On systems that don't support fchdir,
+passing handles produces a fatal error at run time.
+
=item chmod LIST
Changes the permissions of a list of files. The first element of the
list must be the numerical mode, which should probably be an octal
-number, and which definitely should I<not> a string of octal digits:
+number, and which definitely should I<not> be a string of octal digits:
C<0644> is okay, C<'0644'> is not. Returns the number of files
successfully changed. See also L</oct>, if all you have is a string.
$mode = '0644'; chmod oct($mode), 'foo'; # this is better
$mode = 0644; chmod $mode, 'foo'; # this is best
+On systems that support fchmod, you might pass file handles among the
+files. On systems that don't support fchmod, passing file handles
+produces a fatal error at run time.
+
+ open(my $fh, "<", "foo");
+ my $perm = (stat $fh)[2] & 07777;
+ chmod($perm | 0600, $fh);
+
You can also import the symbolic C<S_I*> constants from the Fcntl
module:
$cnt = chown $uid, $gid, 'foo', 'bar';
chown $uid, $gid, @filenames;
+On systems that support fchown, you might pass file handles among the
+files. On systems that don't support fchown, passing file handles
+produces a fatal error at run time.
+
Here's an example that looks up nonnumeric uids in the passwd file:
print "User: ";
to 255 (inclusive) are by default not encoded in UTF-8 Unicode for
backward compatibility reasons (but see L<encoding>).
+Negative values give the Unicode replacement character (chr(0xfffd)),
+except under the L</bytes> pragma, where low eight bits of the value
+(truncated to an integer) are used.
+
If NUMBER is omitted, uses C<$_>.
For the reverse, use L</ord>.
program exited non-zero, C<$!> will be set to C<0>.) Closing a pipe
also waits for the process executing on the pipe to complete, in case you
want to look at the output of the pipe afterwards, and
-implicitly puts the exit status value of that command into C<$?>.
+implicitly puts the exit status value of that command into C<$?> and
+C<${^CHILD_ERROR_NATIVE}>.
Prematurely closing the read end of a pipe (i.e. before the process
writing to it at the other end has closed it) will result in a
is sometimes preferable to matching particular string values of $@ using
regular expressions. Here's an example:
+ use Scalar::Util 'blessed';
+
eval { ... ; die Some::Module::Exception->new( FOO => "bar" ) };
if ($@) {
- if (ref($@) && UNIVERSAL::isa($@,"Some::Module::Exception")) {
+ if (blessed($@) && $@->isa("Some::Module::Exception")) {
# handle Some::Module::Exception
}
else {
=item do EXPR
Uses the value of EXPR as a filename and executes the contents of the
-file as a Perl script. Its primary use is to include subroutines
-from a Perl subroutine library.
+file as a Perl script.
do 'stat.pl';
eval `cat stat.pl`;
except that it's more efficient and concise, keeps track of the current
-filename for error messages, searches the @INC libraries, and updates
+filename for error messages, searches the @INC directories, and updates
C<%INC> if the file is found. See L<perlvar/Predefined Names> for these
variables. It also differs in that code evaluated with C<do FILENAME>
cannot see lexicals in the enclosing scope; C<eval STRING> does. It's the
=item eval BLOCK
+=item eval
+
In the first form, the return value of EXPR is parsed and executed as if it
were a little Perl program. The value of the expression (which is itself
determined within scalar context) is first parsed, and if there weren't any
=item exit EXPR
+=item exit
+
Evaluates EXPR and exits immediately with that value. Example:
$ans = <STDIN>;
Internet domain, each address is four bytes long and you can unpack it
by saying something like:
- ($a,$b,$c,$d) = unpack('C4',$addr[0]);
+ ($a,$b,$c,$d) = unpack('W4',$addr[0]);
The Socket library makes this slightly easier:
An example testing if Nagle's algorithm is turned on on a socket:
- use Socket;
+ use Socket qw(:all);
defined(my $tcp = getprotobyname("tcp"))
or die "Could not determine the protocol number for tcp";
- # my $tcp = Socket::IPPROTO_TCP; # Alternative
- my $packed = getsockopt($socket, $tcp, Socket::TCP_NODELAY)
- or die "Could not query TCP_NODELAY SOCKEt option: $!";
+ # my $tcp = IPPROTO_TCP; # Alternative
+ my $packed = getsockopt($socket, $tcp, TCP_NODELAY)
+ or die "Could not query TCP_NODELAY socket option: $!";
my $nodelay = unpack("I", $packed);
print "Nagle's algorithm is turned ", $nodelay ? "off\n" : "on\n";
=item gmtime EXPR
+=item gmtime
+
Converts a time as returned by the time function to an 8-element list
with the time localized for the standard Greenwich time zone.
Typically used as follows:
instead a Perl builtin. To get somewhat similar but locale dependent date
strings, see the example in L</localtime>.
+See L<perlport/gmtime> for portability concerns.
+
=item goto LABEL
=item goto EXPR
=item hex
Interprets EXPR as a hex string and returns the corresponding value.
-(To convert strings that might start with either 0, 0x, or 0b, see
+(To convert strings that might start with either C<0>, C<0x>, or C<0b>, see
L</oct>.) If EXPR is omitted, uses C<$_>.
print hex '0xAf'; # prints '175'
Hex strings may only represent integers. Strings that would cause
integer overflow trigger a warning. Leading whitespace is not stripped,
-unlike oct().
+unlike oct(). To present something as hex, look into L</printf>,
+L</sprintf>, or L</unpack>.
-=item import
+=item import LIST
There is no builtin C<import> function. It is just an ordinary
method (subroutine) defined (or inherited) by modules that wish to export
Implements the ioctl(2) function. You'll probably first have to say
- require "ioctl.ph"; # probably in /usr/local/lib/perl/ioctl.ph
+ require "sys/ioctl.ph"; # probably in $Config{archlib}/ioctl.ph
-to get the correct function definitions. If F<ioctl.ph> doesn't
+to get the correct function definitions. If F<sys/ioctl.ph> doesn't
exist or doesn't have the correct definitions you'll have to roll your
own, based on your C header files such as F<< <sys/ioctl.h> >>.
(There is a Perl script called B<h2ph> that comes with the Perl kit that
=item localtime EXPR
+=item localtime
+
Converts a time as returned by the time function to a 9-element list
with the time analyzed for the local time zone. Typically used as
follows:
# 0 1 2 3 4 5 6 7 8
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
- localtime(time);
+ localtime(time);
All list elements are numeric, and come straight out of the C `struct
-tm'. $sec, $min, and $hour are the seconds, minutes, and hours of the
-specified time. $mday is the day of the month, and $mon is the month
-itself, in the range C<0..11> with 0 indicating January and 11
-indicating December. $year is the number of years since 1900. That
-is, $year is C<123> in year 2023. $wday is the day of the week, with
-0 indicating Sunday and 3 indicating Wednesday. $yday is the day of
-the year, in the range C<0..364> (or C<0..365> in leap years.) $isdst
-is true if the specified time occurs during daylight savings time,
-false otherwise.
+tm'. C<$sec>, C<$min>, and C<$hour> are the seconds, minutes, and hours
+of the specified time.
-Note that the $year element is I<not> simply the last two digits of
-the year. If you assume it is, then you create non-Y2K-compliant
-programs--and you wouldn't want to do that, would you?
+C<$mday> is the day of the month, and C<$mon> is the month itself, in
+the range C<0..11> with 0 indicating January and 11 indicating December.
+This makes it easy to get a month name from a list:
-The proper way to get a complete 4-digit year is simply:
+ my @abbr = qw( Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec );
+ print "$abbr[$mon] $mday";
+ # $mon=9, $mday=18 gives "Oct 18"
- $year += 1900;
+C<$year> is the number of years since 1900, not just the last two digits
+of the year. That is, C<$year> is C<123> in year 2023. The proper way
+to get a complete 4-digit year is simply:
-And to get the last two digits of the year (e.g., '01' in 2001) do:
+ $year += 1900;
- $year = sprintf("%02d", $year % 100);
+To get the last two digits of the year (e.g., '01' in 2001) do:
+
+ $year = sprintf("%02d", $year % 100);
+
+C<$wday> is the day of the week, with 0 indicating Sunday and 3 indicating
+Wednesday. C<$yday> is the day of the year, in the range C<0..364>
+(or C<0..365> in leap years.)
+
+C<$isdst> is true if the specified time occurs during Daylight Saving
+Time, false otherwise.
If EXPR is omitted, C<localtime()> uses the current time (C<localtime(time)>).
Note that the C<%a> and C<%b>, the short forms of the day of the week
and the month of the year, may not necessarily be three characters wide.
+See L<perlport/localtime> for portability concerns.
+
=item lock THING
This function places an advisory lock on a shared variable, or referenced
=item mkdir FILENAME
+=item mkdir
+
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<$!> (errno).
-If omitted, MASK defaults to 0777.
+If omitted, MASK defaults to 0777. If omitted, FILENAME defaults
+to C<$_>.
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
}
}
-See L<perliol/> for detailed info on PerlIO.
+See L<perliol> for detailed info on PerlIO.
You may also, in the Bourne shell tradition, specify an EXPR beginning
with C<< '>&' >>, in which case the rest of the string is interpreted
of $^F. See L<perlvar/$^F>.
Closing any piped filehandle causes the parent process to wait for the
-child to finish, and returns the status value in C<$?>.
+child to finish, and returns the status value in C<$?> and
+C<${^CHILD_ERROR_NATIVE}>.
The filename passed to 2-argument (or 1-argument) form of open() will
have leading and trailing whitespace deleted, and the normal
=item our TYPE EXPR : ATTRS
-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.)
+C<our> associates a simple name with a package variable in the current
+package for the remander of the lexical scope. The listed variables
+are declared 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. When C<use strict
+'vars'> is in effect, the C<our> declaration 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.)
+
+If more than one value is listed, the list must be placed in
+parentheses.
+
+ our $foo;
+ our($bar, $baz);
An C<our> declaration declares a global variable that will be visible
across its entire lexical scope, even across package boundaries. The
$bar = 20;
package Bar;
- print $bar; # prints 20
+ print $bar; # prints 20 as it refers to $Foo::bar
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
+if they are in different packages. If they happen to be in the same
package, Perl will emit warnings if you have asked for them.
use warnings;
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.
+an integer may be represented by a sequence of 4 bytes which will be
+converted to a sequence of 4 characters.
The TEMPLATE is a sequence of characters that give the order and type
of values, as follows:
H A hex string (high nybble first).
c A signed char (8-bit) value.
- C An unsigned char value. Only does bytes. See U for Unicode.
+ C An unsigned C char (octet) even under Unicode. Should normally not
+ be used. See U and W instead.
+ W An unsigned char value (can be greater than 255).
s A signed short (16-bit) value.
S An unsigned short value.
U A Unicode character number. Encodes to UTF-8 internally
(or UTF-EBCDIC in EBCDIC platforms).
- w A BER compressed integer. Its bytes represent an unsigned
- integer in base 128, most significant digit first, with as
- few digits as possible. Bit eight (the high bit) is set
- on each byte except the last.
+ w A BER compressed integer (not an ASN.1 BER, see perlpacktut for
+ details). Its bytes represent an unsigned integer in base 128,
+ most significant digit first, with as few digits as possible. Bit
+ eight (the high bit) is set on each byte except the last.
x A null byte.
X Back up a byte.
- @ Null fill to absolute position, counted from the start of
- the innermost ()-group.
+ @ Null fill or truncate to absolute position, counted from the
+ start of the innermost ()-group.
+ . Null fill or truncate to absolute position specified by value.
( Start of a ()-group.
Some letters in the TEMPLATE may optionally be followed by one or
nNvV Treat integers as signed instead of unsigned.
+ @. Specify position as byte offset in the internal
+ representation of the packed string. Efficient but
+ dangerous.
+
> sSiIlLqQ Force big-endian byte-order on the type.
jJfFdDpP (The "big end" touches the construct.)
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>, C<@>, C<x>, C<X> 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, 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). A numeric repeat count may optionally be enclosed in
-brackets, as in C<pack 'C[80]', @arr>.
+C<H>, C<@>, C<.>, C<x>, C<X> 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, except for C<@>, C<x>, C<X>, where it
+is equivalent to C<0>, for <.> where it means relative to string start
+and C<u>, where it is equivalent to 1 (or 45, which is the same).
+A numeric repeat count may optionally be enclosed in brackets, as in
+C<pack 'C[80]', @arr>.
One can replace the numeric repeat count by a template enclosed in brackets;
then the packed length of this template in bytes is used as a count.
byte (so the packed result will be one longer than the byte C<length>
of the item).
+When used with C<@>, the repeat count represents an offset from the start
+of the innermost () group.
+
+When used with C<.>, the repeat count is used to determine the starting
+position from where the value offset is calculated. If the repeat count
+is 0, it's relative to the current position. If the repeat count is C<*>,
+the offset is relative to the start of the packed string. And if its an
+integer C<n> the offset is relative to the start of the n-th innermost
+() group (or the start of the string if C<n> is bigger then the group
+level).
+
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.
+to encode per line of output, with 0, 1 and 2 replaced by 45. The repeat
+count should not be more than 65.
=item *
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. When packing,
-C<a>, and C<Z> are equivalent.
+unpacking, C<A> strips trailing whitespace and nulls, C<Z> strips everything
+after the first null, and C<a> returns data verbatim.
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.
+by a null byte. Thus C<Z> always packs a trailing null (except when the
+count is 0).
=item *
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 character 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($byte)%2>. In particular, bytes C<"0"> and
-C<"1"> generate bits 0 and 1, as do bytes C<"\0"> and C<"\1">.
+input character, i.e., on C<ord($char)%2>. In particular, characters C<"0">
+and C<"1"> generate bits 0 and 1, as do characters 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.
+of characters is converted to 1 character of output. With format C<b>
+the first character of the 8-tuple determines the least-significant bit of a
+character, and with format C<B> it determines the most-significant bit of
+a character.
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
+remainder is packed as if the input string were padded by null characters
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.
+If the input string of pack() is longer than needed, extra characters are
+ignored. A C<*> for the repeat count of pack() means to use all the
+characters 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,
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($byte)%16>. In particular,
-bytes C<"0"> and C<"1"> generate nybbles 0 and 1, as do bytes
-C<"\0"> and C<"\1">. For bytes C<"a".."f"> and C<"A".."F"> the result
+Each character of the input field of pack() generates 4 bits of the result.
+For non-alphabetical characters the result is based on the 4 least-significant
+bits of the input character, i.e., on C<ord($char)%16>. In particular,
+characters C<"0"> and C<"1"> generate nybbles 0 and 1, as do bytes
+C<"\0"> and C<"\1">. For characters 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<"A"> both generate the nybble C<0xa==10>. The result for characters
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
+of characters is converted to 1 character of output. With format C<h> the
+first character of the pair determines the least-significant nybble of the
+output character, 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"
+by a null character 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
+If the input string of pack() is longer than needed, extra characters are
+ignored.
+A C<*> for the repeat count of pack() means to use all the characters of
+the input field. On unpack()ing the nybbles are converted to a string
of hexadecimal digits.
=item *
=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 C</> template character allows packing and unpacking of a sequence of
+items where the packed structure contains a packed item count followed by
+the packed items themselves.
+You write I<length-item>C</>I<sequence-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).
-For C<pack>, 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. For all other
-codes, C<unpack> applies the length value to the next item, which must not
-have a repeat count.
+For C<pack>, the I<sequence-item> may have a repeat count, in which case
+the minimum of that and the number of available items is used as argument
+for the I<length-item>. If it has no repeat count or uses a '*', the number
+of available items is used. For C<unpack> the repeat count is always obtained
+by decoding the packed item count, and the I<sequence-item> must not have a
+repeat count.
+
+If the I<sequence-item> refers to a string type (C<"A">, C<"a"> or C<"Z">),
+the I<length-item> is a string length, not a number of strings. If there is
+an explicit repeat count for pack, the packed string will be adjusted to that
+given length.
- 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 'W/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"
+ pack 'a/W2', ord('a') .. ord('z'); gives '2ab'
The I<length-item> is not returned explicitly from C<unpack>.
You can see your system's preference with
print join(" ", map { sprintf "%#02x", $_ }
- unpack("C*",pack("L",0x12345678))), "\n";
+ unpack("W*",pack("L",0x12345678))), "\n";
The byteorder on the platform where Perl was built is also available
via L<Config>:
If you want portable packed integers you can either use the formats
C<n>, C<N>, C<v>, and C<V>, or you can use the C<E<gt>> and C<E<lt>>
-modifiers. These modifiers are only available as of perl 5.8.5.
+modifiers. These modifiers are only available as of perl 5.9.2.
See also L<perlport>.
=item *
=item *
-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.
+Pack and unpack can operate in two modes, character mode (C<C0> mode) where
+the packed string is processed per character and UTF-8 mode (C<U0> mode)
+where the packed string is processed in its UTF-8-encoded Unicode form on
+a byte by byte basis. Character mode is the default unless the format string
+starts with an C<U>. You can switch mode at any moment with an explicit
+C<C0> or C<U0> in the format. A mode is in effect until the next mode switch
+or until the end of the ()-group in which it was entered.
=item *
You must yourself do any alignment or padding by inserting for example
enough C<'x'>es while packing. There is no way to pack() and unpack()
-could know where the bytes are going to or coming from. Therefore
+could know where the characters are going to or coming from. Therefore
C<pack> (and C<unpack>) handle their output and input as flat
-sequences of bytes.
+sequences of characters.
=item *
is the string "\0a\0\0bc".
-
=item *
C<x> and C<X> accept C<!> modifier. In this case they act as
alignment commands: they jump forward/back to the closest position
-aligned at a multiple of C<count> bytes. For example, to pack() or
+aligned at a multiple of C<count> characters. For example, to pack() or
unpack() C's C<struct {char c; double d; char cc[2]}> one may need to
-use the template C<C x![d] d C[2]>; this assumes that doubles must be
+use the template C<W x![d] d W[2]>; this assumes that doubles must be
aligned on the double's size.
For alignment commands C<count> of 0 is equivalent to C<count> of 1;
Examples:
- $foo = pack("CCCC",65,66,67,68);
+ $foo = pack("WWWW",65,66,67,68);
# foo eq "ABCD"
- $foo = pack("C4",65,66,67,68);
+ $foo = pack("W4",65,66,67,68);
# same thing
+ $foo = pack("W4",0x24b6,0x24b7,0x24b8,0x24b9);
+ # same thing with Unicode circled letters.
$foo = pack("U4",0x24b6,0x24b7,0x24b8,0x24b9);
- # same thing with Unicode circled letters
+ # same thing with Unicode circled letters. You don't get the UTF-8
+ # bytes because the U at the start of the format caused a switch to
+ # U0-mode, so the UTF-8 bytes get joined into characters
+ $foo = pack("C0U4",0x24b6,0x24b7,0x24b8,0x24b9);
+ # foo eq "\xe2\x92\xb6\xe2\x92\xb7\xe2\x92\xb8\xe2\x92\xb9"
+ # This is the UTF-8 encoding of the string in the previous example
$foo = pack("ccxxcc",65,66,67,68);
# foo eq "AB\0\0CD"
- # note: the above examples featuring "C" and "c" are true
+ # note: the above examples featuring "W" and "c" are true
# only on ASCII and ASCII-derived systems such as ISO Latin 1
# and UTF-8. In EBCDIC the first example would be
- # $foo = pack("CCCC",193,194,195,196);
+ # $foo = pack("WWWW",193,194,195,196);
$foo = pack("s2",1,2);
# "\1\0\2\0" on little-endian
$bar = pack('s@4l', 12, 34);
# short 12, zero fill to position 4, long 34
# $foo eq $bar
+ $baz = pack('s.l', 12, 4, 34);
+ # short 12, zero fill to position 4, long 34
$foo = pack('nN', 42, 4711);
# pack big-endian 16- and 32-bit unsigned integers
=item pos
Returns the offset of where the last C<m//g> search left off for the variable
-in question (C<$_> is used when the variable is not specified). May be
-modified to change that offset. Such modification will also influence
-the C<\G> zero-width assertion in regular expressions. See L<perlre> and
+in question (C<$_> is used when the variable is not specified). Note that
+0 is a valid match offset, while C<undef> indicates that the search position
+is reset (usually due to match failure, but can also be because no match has
+yet been performed on the scalar). C<pos> directly accesses the location used
+by the regexp engine to store the offset, so assigning to C<pos> will change
+that offset, and so will also influence the C<\G> zero-width assertion in
+regular expressions. Because a failed C<m//gc> match doesn't reset the offset,
+the return from C<pos> won't change either in this case. See L<perlre> and
L<perlop>.
=item print FILEHANDLE LIST
the print--interpose a C<+> or put parentheses around all the
arguments.
-Note that if you're storing FILEHANDLES in an array or other expression,
-you will have to use a block returning its value instead:
+Note that if you're storing FILEHANDLEs in an array, or if you're using
+any other expression more complex than a scalar variable to retrieve it,
+you will have to use a block returning the filehandle value instead:
print { $files[$i] } "stuff\n";
print { $OK ? STDOUT : STDERR } "stuff\n";
unless (ref($r)) {
print "r is not a reference at all.\n";
}
- if (UNIVERSAL::isa($r, "HASH")) { # for subclassing
- print "r is a reference to something that isa hash.\n";
- }
See also L<perlref>.
behind the scenes. Before C<require> looks for a "F<.pm>" extension,
it will first look for a filename with a "F<.pmc>" extension. A file
with this extension is assumed to be Perl bytecode generated by
-L<B::Bytecode|B::Bytecode>. If this file is found, and it's modification
+L<B::Bytecode|B::Bytecode>. If this file is found, and its modification
time is newer than a coinciding "F<.pm>" non-compiled file, it will be
loaded in place of that non-compiled file ending in a "F<.pm>" extension.
is implementation-dependent. See also L<perlport> for notes on the
portability of C<select>.
+On error, C<select> returns C<undef> and sets C<$!>.
+
+Note: on some Unixes, the select(2) system call may report a socket file
+descriptor as "ready for reading", when actually no data is available,
+thus a subsequent read blocks. It can be avoided using always the
+O_NONBLOCK flag on the socket. See select(2) and fcntl(2) for further
+details.
+
B<WARNING>: One should not attempt to mix buffered I/O (like C<read>
or <FH>) with C<select>, except as permitted by POSIX, and even
then only on POSIX systems. You have to use C<sysread> instead.
Splits the string EXPR into a list of strings and returns that list. By
default, empty leading fields are preserved, and empty trailing ones are
-deleted.
+deleted. (If all fields are empty, they are considered to be trailing.)
In scalar context, returns the number of fields found and splits into
the C<@_> array. Use of split in scalar context is deprecated, however,
produces the output 'h:i:t:h:e:r:e'.
-Using the empty pattern C<//> specifically matches the null string, and is
-not be confused with the use of C<//> to mean "the last successful pattern
-match".
+As a special case for C<split>, using the empty pattern C<//> specifically
+matches only the null string, and is not be confused with the regular use
+of C<//> to mean "the last successful pattern match". So, for C<split>,
+the following:
-Empty leading (or trailing) fields are produced when there are positive width
-matches at the beginning (or end) of the string; a zero-width match at the
-beginning (or end) of the string does not produce an empty field. For
-example:
+ print join(':', split(//, 'hi there'));
+
+produces the output 'h:i: :t:h:e:r:e'.
+
+Empty leading (or trailing) fields are produced when there are positive
+width matches at the beginning (or end) of the string; a zero-width match
+at the beginning (or end) of the string does not produce an empty field.
+For example:
print join(':', split(/(?=\w)/, 'hi there!'));
(The epoch was at 00:00 January 1, 1970 GMT.)
-(*) The ctime field is non-portable. In particular, you cannot expect
-it to be a "creation time", see L<perlport/"Files and Filesystems">
-for details.
+(*) Not all fields are supported on all filesystem types. Notably, the
+ctime field is non-portable. In particular, you cannot expect it to be a
+"creation time", see L<perlport/"Files and Filesystems"> for details.
If C<stat> is passed the special filehandle consisting of an underline, no
stat is done, but the current contents of the stat structure from the
Some of the most common values are C<O_RDONLY> for opening the file in
read-only mode, C<O_WRONLY> for opening the file in write-only mode,
-and C<O_RDWR> for opening the file in read-write mode, and.
+and C<O_RDWR> for opening the file in read-write mode.
For historical reasons, some values work on almost every system
supported by perl: zero means read-only, one means write-only, and two
In many systems the C<O_EXCL> flag is available for opening files in
exclusive mode. This is B<not> locking: exclusiveness means here that
-if the file already exists, sysopen() fails. The C<O_EXCL> wins
-C<O_TRUNC>.
+if the file already exists, sysopen() fails. C<O_EXCL> may not work
+on network filesystems, and has no effect unless the C<O_CREAT> flag
+is set as well. Setting C<O_CREAT|O_EXCL> prevents the file from
+being opened if it is a symbolic link. It does not protect against
+symbolic links in the file's path.
-Sometimes you may want to truncate an already-existing file: C<O_TRUNC>.
+Sometimes you may want to truncate an already-existing file. This
+can be done using the C<O_TRUNC> flag. The behavior of
+C<O_TRUNC> with C<O_RDONLY> is undefined.
You should seldom if ever use C<0644> as argument to C<sysopen>, because
that takes away the user's option to have a more permissive umask.
that would render sysseek() very slow).
sysseek() bypasses normal buffered IO, so mixing this with reads (other
-than C<sysread>, for example
>< or read()) C<print>, C<write>,
+than C<sysread>, for example
C<< <> >> or read()) C<print>, C<write>,
C<seek>, C<tell>, or C<eof> may cause confusion.
For WHENCE, you may also use the constants C<SEEK_SET>, C<SEEK_CUR>,
printf "child exited with value %d\n", $? >> 8;
}
-or more portably by using the W*() calls of the POSIX extension;
-see L<perlport> for more information.
+Alternatively you might inspect the value of C<${^CHILD_ERROR_NATIVE}>
+with the W*() calls of the POSIX extension.
When the arguments get executed via the system shell, results
and return codes will be subject to its quirks and capabilities.
There is no C<systell> function. Use C<sysseek(FH, 0, 1)> for that.
-Do not use tell() on a filehandle that has been opened using
-sysopen(), use sysseek() for that as described above. Why? Because
-sysopen() creates unbuffered, "raw", filehandles, while open() creates
-buffered filehandles. sysseek() make sense only on the first kind,
-tell() only makes sense on the second kind.
+Do not use tell() (or other buffered I/O operations) on a file handle
+that has been manipulated by sysread(), syswrite() or sysseek().
+Those functions ignore the buffering, while tell() does not.
=item telldir DIRHANDLE
=item time
Returns the number of non-leap seconds since whatever time the system
-considers to be the epoch (that's 00:00:00, January 1, 1904 for Mac OS,
-and 00:00:00 UTC, January 1, 1970 for most other systems).
-Suitable for feeding to C<gmtime> and C<localtime>.
+considers to be the epoch, suitable for feeding to C<gmtime> and
+C<localtime>. On most systems the epoch is 00:00:00 UTC, January 1, 1970;
+a prominent exception being Mac OS Classic which uses 00:00:00, January 1,
+1904 in the current local time zone for its epoch.
For measuring time in better granularity than one second,
you may use either the Time::HiRes module (from CPAN, and starting from
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
+of C<pack>, or the characters of the string represent a C structure of some
kind.
The TEMPLATE has the same format as in the C<pack> function.
and then there's
- sub ordinal { unpack("c",$_[0]); } # same as ord()
+ sub ordinal { unpack("W",$_[0]); } # same as ord()
In addition to fields allowed in pack(), you may prefix a field with
a %<number> to indicate that
$checksum = do {
local $/; # slurp!
- unpack("%32C*",<>) % 65535;
+ unpack("%32W*",<>) % 65535;
};
The following efficiently counts the number of set bits in a bit vector:
and modification times, in that order. Returns the number of files
successfully changed. The inode change time of each file is set
to the current time. For example, this code has the same effect as the
-Unix touch(1) command when the files I<already exist>.
+Unix touch(1) command when the files I<already exist> and belong to
+the user running the program:
#!/usr/bin/perl
$atime = $mtime = time;
the utime(2) function in the C library will be called with a null second
argument. On most systems, this will set the file's access and
modification times to the current time (i.e. equivalent to the example
-above.)
+above) and will even work on other users' files where you have write
+permission:
utime undef, undef, @ARGV;
Behaves like the wait(2) system call on your system: it waits for a child
process to terminate and returns the pid of the deceased process, or
-C<-1> if there are no child processes. The status is returned in C<$?>.
+C<-1> if there are no child processes. The status is returned in C<$?>
+and C<{^CHILD_ERROR_NATIVE}>.
Note that a return value of C<-1> could mean that child processes are
being automatically reaped, as described in L<perlipc>.
Waits for a particular child process to terminate and returns the pid of
the deceased process, or C<-1> if there is no such child process. On some
systems, a value of 0 indicates that there are processes still running.
-The status is returned in C<$?>. If you say
+The status is returned in C<$?> and C<{^CHILD_ERROR_NATIVE}>. If you say
use POSIX ":sys_wait_h";
#...
=item wantarray
Returns true if the context of the currently executing subroutine or
-eval() block is looking for a list value. Returns false if the context is
+C<eval> is looking for a list value. Returns false if the context is
looking for a scalar. Returns the undefined value if the context is
looking for no value (void context).
my @a = complex_calculation();
return wantarray ? @a : "@a";
+C<wantarray()>'s result is unspecified in the top level of a file,
+in a C<BEGIN>, C<CHECK>, C<INIT> or C<END> block, or in a C<DESTROY>
+method.
+
This function should have been named wantlist() instead.
=item warn LIST
https://perl5.git.perl.org / perl5.git / blobdiff