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.
=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
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 ", $nodelay ? "off\n" : "on\n";
=item hex
Interprets EXPR as a hex string and returns the corresponding value.
-(To convert strings that might start with either 0, 0x, or 0b, see
+(To convert strings that might start with either C<0>, C<0x>, or C<0b>, see
L</oct>.) If EXPR is omitted, uses C<$_>.
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 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)>).
}
}
-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
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.
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.
+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>:
=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 *
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);
$foo = pack("s2",1,2);
# "\1\0\2\0" on little-endian
=item pos
Returns the offset of where the last C<m//g> search left off for the variable
-in question (C<$_> 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<$_> is used when the variable is not specified). Note that
+0 is a valid match offset, while C<undef> indicates that the search position
+is reset (usually due to match failure, but can also be because no match has
+yet been performed on the scalar). C<pos> directly accesses the location used
+by the regexp engine to store the offset, so assigning to C<pos> will change
+that offset, and so will also influence the C<\G> zero-width assertion in
+regular expressions. Because a failed C<m//gc> match doesn't reset the offset,
+the return from C<pos> won't change either in this case. See L<perlre> and
L<perlop>.
=item print FILEHANDLE LIST
(The epoch was at 00:00 January 1, 1970 GMT.)
-(*) The ctime field is non-portable. In particular, you cannot expect
-it to be a "creation time", see L<perlport/"Files and Filesystems">
-for details.
+(*) Not all fields are supported on all filesystem types. Notably, the
+ctime field is non-portable. In particular, you cannot expect it to be a
+"creation time", see L<perlport/"Files and Filesystems"> for details.
If C<stat> is passed the special filehandle consisting of an underline, no
stat is done, but the current contents of the stat structure from the
that would render sysseek() very slow).
sysseek() bypasses normal buffered IO, so mixing this with reads (other
-than C<sysread>, for example
>< or read()) C<print>, C<write>,
+than C<sysread>, for example
C<< <> >> or read()) C<print>, C<write>,
C<seek>, C<tell>, or C<eof> may cause confusion.
For WHENCE, you may also use the constants C<SEEK_SET>, C<SEEK_CUR>,
The string is broken into chunks described by the TEMPLATE. Each chunk
is converted separately to a value. Typically, either the string is a result
-of C<pack>, or the bytes of the string represent a C structure of some
+of C<pack>, or the characters of the string represent a C structure of some
kind.
The TEMPLATE has the same format as in the C<pack> function.
and then there's
- sub ordinal { unpack("c",$_[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:
=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