C<do>, C<import>, C<no>, C<package>, C<require>, C<use>
-=item Keywords related to classes and object-orientedness
+=item Keywords related to classes and object-orientation
X<object> X<class> X<package>
C<bless>, C<dbmclose>, C<dbmopen>, C<package>, C<ref>, C<tie>, C<tied>,
The interpretation of the file permission operators C<-r>, C<-R>,
C<-w>, C<-W>, C<-x>, and C<-X> is by default based solely on the mode
of the file and the uids and gids of the user. There may be other
-reasons you can't actually read, write, or execute the file. Such
-reasons may be for example network filesystem access controls, ACLs
-(access control lists), read-only filesystems, and unrecognized
-executable formats.
+reasons you can't actually read, write, or execute the file: for
+example network filesystem access controls, ACLs (access control lists),
+read-only filesystems, and unrecognized executable formats. Note
+that the use of these six specific operators to verify if some operation
+is possible is usually a mistake, because it may be open to race
+conditions.
Also note that, for the superuser on the local filesystems, the C<-r>,
C<-R>, C<-w>, and C<-W> tests always return 1, and C<-x> and C<-X> return 1
access() family of system calls. Also note that the C<-x> and C<-X> may
under this pragma return true even if there are no execute permission
bits set (nor any extra execute permission ACLs). This strangeness is
-due to the underlying system calls' definitions. Read the
-documentation for the C<filetest> pragma for more information.
+due to the underlying system calls' definitions. Note also that, due to
+the implementation of C<use filetest 'access'>, the C<_> special
+filehandle won't cache the results of the file tests when this pragma is
+in effect. Read the documentation for the C<filetest> pragma for more
+information.
Note that C<-s/a/b/> does not do a negated substitution. Saying
C<-exp($foo)> still works as expected, however--only single letters
C<$is_require> are set: C<$is_require> is true if the frame is created by a
C<require> or C<use> statement, $evaltext contains the text of the
C<eval EXPR> statement. In particular, for an C<eval BLOCK> statement,
-$filename is C<(eval)>, but $evaltext is undefined. (Note also that
+$subroutine 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.) $subroutine may also be C<(unknown)> if this particular
subroutine happens to have been deleted from the symbol table.
=item each HASH
X<each> X<hash, iterator>
+=item each ARRAY
+X<array, iterator>
+
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 only the key for the next
-element in the hash.
+key and value for the next element of a hash, or the index and value for
+the next element of an array, so that you can iterate over it. When called
+in scalar context, returns only the key for the next element in the hash
+(or the index for an array).
-Entries are returned in an apparently random order. The actual random
+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 to be in the same order as either the C<keys> or C<values>
function would produce on the same (unmodified) hash. Since Perl
-5.8.1 the ordering is different even between different runs of Perl
+5.8.2 the ordering can be different even between different runs of Perl
for security reasons (see L<perlsec/"Algorithmic Complexity Attacks">).
-When the hash is entirely read, a null array is returned in list context
-(which when assigned produces a false (C<0>) value), and C<undef> in
+When the hash or array is entirely read, a null array is returned in list
+context (which when assigned produces a false (C<0>) value), and C<undef> in
scalar context. The next call to C<each> after that will start iterating
-again. There is a single iterator for each hash, shared by all C<each>,
-C<keys>, and C<values> function calls in the program; it can be reset by
-reading all the elements from the hash, or by evaluating C<keys HASH> or
-C<values HASH>. If you add or delete elements of a hash while you're
+again. There is a single iterator for each hash or array, shared by all
+C<each>, C<keys>, and C<values> function calls in the program; it can be
+reset by reading all the elements from the hash or array, or by evaluating
+C<keys HASH>, C<values HASH>, C<keys ARRAY>, or C<values ARRAY>. If you add
+or delete elements of a hash while you're
iterating over it, you may get entries skipped or duplicated, so
don't. Exception: It is always safe to delete the item most recently
returned by C<each()>, which means that the following code will work:
flock(MBOX,LOCK_UN);
}
- open(MBOX, ">>/usr/spool/mail/$ENV{'USER'}")
+ open(my $mbox, ">>", "/usr/spool/mail/$ENV{'USER'}")
or die "Can't open mailbox: $!";
lock();
- print MBOX $msg,"\n\n";
+ print $mbox $msg,"\n\n";
unlock();
On systems that support a real flock(), locks are inherited across fork()
=item keys HASH
X<keys> X<key>
-Returns a list consisting of all the keys of the named hash.
-(In scalar context, returns the number of keys.)
+=item keys ARRAY
+
+Returns a list consisting of all the keys of the named hash, or the indices
+of an array. (In scalar context, returns the number of keys or indices.)
-The keys are returned in an apparently random order. The actual
+The keys of a hash are returned in an apparently random order. The actual
random order is subject to change in future versions of perl, but it
is guaranteed to be the same order as either the C<values> or C<each>
function produces (given that the hash has not been modified). Since
Perl for security reasons (see L<perlsec/"Algorithmic Complexity
Attacks">).
-As a side effect, calling keys() resets the HASH's internal iterator
+As a side effect, calling keys() resets the HASH or ARRAY's internal iterator
(see L</each>). In particular, calling keys() in void context resets
the iterator with no other overhead.
%hash> if you want to free the storage while C<%hash> is still in scope.
You can't shrink the number of buckets allocated for the hash using
C<keys> in this way (but you needn't worry about doing this by accident,
-as trying has no effect).
+as trying has no effect). C<keys @array> in an lvalue context is a syntax
+error.
See also C<each>, C<values> and C<sort>.
=item length
Returns the length in I<characters> of the value of EXPR. If EXPR is
-omitted, returns length of C<$_>. Note that this cannot be used on
-an entire array or hash to find out how many elements these have.
-For that, use C<scalar @array> and C<scalar keys %hash> respectively.
+omitted, returns length of C<$_>. If EXPR is undefined, returns C<undef>.
+Note that this cannot be used on an entire array or hash to find out how
+many elements these have. For that, use C<scalar @array> and C<scalar keys
+%hash> respectively.
Note the I<characters>: if the EXPR is in Unicode, you will get the
number of characters, not the number of bytes. To get the length
C<$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)>).
+If EXPR is omitted, C<localtime()> uses the current time (as returned
+by time(3)).
In scalar context, C<localtime()> returns the ctime(3) value:
Opens the file whose filename is given by EXPR, and associates it with
FILEHANDLE.
+Simple examples to open a file for reading:
+
+ open(my $fh, '<', "input.txt") or die $!;
+
+and for writing:
+
+ open(my $fh, '>', "output.txt") or die $!;
+
(The following is a comprehensive reference to open(): for a gentler
introduction you may consider L<perlopentut>.)
that affect how the input and output are processed (see L<open> and
L<PerlIO> for more details). For example
- open(FH, "<:encoding(UTF-8)", "file")
+ open(my $fh, "<:encoding(UTF-8)", "file")
will open the UTF-8 encoded file containing Unicode characters,
see L<perluniintro>. Note that if layers are specified in the
As a special case the 3-arg form with a read/write mode and the third
argument being C<undef>:
- open(TMP, "+>", undef) or die ...
+ open(my $tmp, "+>", undef) or die ...
opens a filehandle to an anonymous temporary file. Also using "+<"
works for symmetry, but you really should consider writing something
open(LOG, '>>/usr/spool/news/twitlog'); # (log is reserved)
# if the open fails, output is discarded
- open(DBASE, '+<', 'dbase.mine') # open for update
+ open(my $dbase, '+<', 'dbase.mine') # open for update
or die "Can't open 'dbase.mine' for update: $!";
- open(DBASE, '+<dbase.mine') # ditto
+ open(my $dbase, '+<dbase.mine') # ditto
or die "Can't open 'dbase.mine' for update: $!";
open(ARTICLE, '-|', "caesar <$article") # decrypt article
#...
sub read_myfile_munged {
my $ALL = shift;
- my $handle = new IO::File;
+ my $handle = IO::File->new;
open($handle, "myfile") or die "myfile: $!";
$first = <$handle>
or return (); # Automatically closed here.
reference to a new anonymous dirhandle.
DIRHANDLEs have their own namespace separate from FILEHANDLEs.
+See example at C<readdir>.
+
=item ord EXPR
X<ord> X<encoding>
C<$::sail> is equivalent to C<$main::sail> (as well as to C<$main'sail>,
still seen in older code).
-If NAMESPACE is omitted, then there is no current package, and all
-identifiers must be fully qualified or lexicals. However, you are
-strongly advised not to make use of this feature. Its use can cause
-unexpected behaviour, even crashing some versions of Perl. It is
-deprecated, and will be removed from a future release.
-
See L<perlmod/"Packages"> for more information about packages, modules,
and classes. See L<perlsub> for other scoping issues.
better prepend the directory in question. Otherwise, because we didn't
C<chdir> there, it would have been testing the wrong file.
- opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!";
- @dots = grep { /^\./ && -f "$some_dir/$_" } readdir(DIR);
- closedir DIR;
+ opendir(my $dh, $some_dir) || die "can't opendir $some_dir: $!";
+ @dots = grep { /^\./ && -f "$some_dir/$_" } readdir($dh);
+ closedir $dh;
=item readline EXPR
Note the I<characters>: depending on the status of the socket, either
(8-bit) bytes or characters are received. By default all sockets
operate on bytes, but for example if the socket has been changed using
-binmode() to operate with the C<:utf8> I/O layer (see the C<open>
-pragma, L<open>), the I/O will operate on UTF-8 encoded Unicode
-characters, not bytes. Similarly for the C<:encoding> pragma:
-in that case pretty much any characters can be read.
+binmode() to operate with the C<:encoding(utf8)> I/O layer (see the
+C<open> pragma, L<open>), the I/O will operate on UTF-8 encoded Unicode
+characters, not bytes. Similarly for the C<:encoding> pragma: in that
+case pretty much any characters can be read.
=item redo LABEL
X<redo>
otherwise.
Note the I<in bytes>: even if the filehandle has been set to
-operate on characters (for example by using the C<:utf8> open
+operate on characters (for example by using the C<:encoding(utf8)> open
layer), tell() will return byte offsets, not character offsets
(because implementing that would render seek() and tell() rather slow).
Note the I<characters>: depending on the status of the socket, either
(8-bit) bytes or characters are sent. By default all sockets operate
on bytes, but for example if the socket has been changed using
-binmode() to operate with the C<:utf8> I/O layer (see L</open>, or the
-C<open> pragma, L<open>), the I/O will operate on UTF-8 encoded
-Unicode characters, not bytes. Similarly for the C<:encoding> pragma:
-in that case pretty much any characters can be sent.
+binmode() to operate with the C<:encoding(utf8)> I/O layer (see
+L</open>, or the C<open> pragma, L<open>), the I/O will operate on UTF-8
+encoded Unicode characters, not bytes. Similarly for the C<:encoding>
+pragma: in that case pretty much any characters can be sent.
=item setpgrp PID,PGRP
X<setpgrp> X<group>
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:
+Empty leading fields are produced when there are positive-width matches at
+the beginning of the string; a zero-width match at the beginning of
+the string does not produce an empty field. For example:
print join(':', split(/(?=\w)/, 'hi there!'));
-produces the output 'h:i :t:h:e:r:e!'.
+produces the output 'h:i :t:h:e:r:e!'. Empty trailing fields, on the other
+hand, are produced when there is a match at the end of the string (and
+when LIMIT is given and is not 0), regardless of the length of the match.
+For example:
+
+ print join(':', split(//, 'hi there!', -1));
+ print join(':', split(/\W/, 'hi there!', -1));
+
+produce the output 'h:i: :t:h:e:r:e:!:' and 'hi:there:', respectively,
+both with an empty trailing field.
The LIMIT parameter can be used to split a line partially
one or more of:
- space prefix positive number with a space
- + prefix positive number with a plus sign
+ space prefix non-negative number with a space
+ + prefix non-negative number with a plus sign
- left-justify within the field
0 use zeros, not spaces, to right-justify
# ensure the leading "0" for any octal,
would use C<$a> for the width, C<$b> for the precision and C<$c>
as the value to format, while:
- print '<%*1$.*s>', $a, $b;
+ printf '<%*1$.*s>', $a, $b;
would use C<$a> for the width and the precision, and C<$b> as the
value to format.
rapidly changing operating system status programs is the usual method. For
example:
- srand (time ^ $$ ^ unpack "%L*", `ps axww | gzip`);
+ srand (time ^ $$ ^ unpack "%L*", `ps axww | gzip -f`);
If you're particularly concerned with this, see the C<Math::TrulyRandom>
module in CPAN.
negative).
Note the I<in bytes>: even if the filehandle has been set to operate
-on characters (for example by using the C<:utf8> I/O layer), tell()
-will return byte offsets, not character offsets (because implementing
-that would render sysseek() very slow).
+on characters (for example by using the C<:encoding(utf8)> I/O layer),
+tell() will return byte offsets, not character offsets (because
+implementing that would render sysseek() very slow).
sysseek() bypasses normal buffered IO, so mixing this with reads (other
than C<sysread>, for example C<< <> >> or read()) C<print>, C<write>,
last read.
Note the I<in bytes>: even if the filehandle has been set to
-operate on characters (for example by using the C<:utf8> open
-layer), tell() will return byte offsets, not character offsets
-(because that would render seek() and tell() rather slow).
+operate on characters (for example by using the C<:encoding(utf8)> open
+layer), tell() will return byte offsets, not character offsets (because
+that would render seek() and tell() rather slow).
The return value of tell() for the standard streams like the STDIN
depends on the operating system: it may return -1 or something else.
Specifying VERSION as a literal of the form v5.6.1 should generally be
avoided, because it leads to misleading error messages under earlier
-versions of Perl that do not support this syntax. The equivalent numeric
-version should be used instead.
+versions of Perl (that is, prior to 5.6.0) that do not support this
+syntax. The equivalent numeric version should be used instead.
use v5.6.1; # compile time version check
use 5.6.1; # ditto
use 5.006_001; # ditto; preferred for backwards 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.)
+C<use>ing library modules that won't work with older versions of Perl.
+(We try not to do this more than we have to.)
Also, if the specified perl version is greater than or equal to 5.9.5,
C<use VERSION> will also load the C<feature> pragma and enable all
=item values HASH
X<values>
-Returns a list consisting of all the values of the named hash.
-(In a scalar context, returns the number of values.)
+=item values ARRAY
+
+Returns a list consisting of all the values of the named hash, or the values
+of an array. (In a scalar context, returns the number of values.)
The values are returned in an apparently random order. The actual
random order is subject to change in future versions of perl, but it
5.8.1 the ordering is different even between different runs of Perl
for security reasons (see L<perlsec/"Algorithmic Complexity Attacks">).
-As a side effect, calling values() resets the HASH's internal iterator,
+As a side effect, calling values() resets the HASH or ARRAY's internal
+iterator,
see L</each>. (In particular, calling values() in void context resets
-the iterator with no other overhead.)
+the iterator with no other overhead. Apart from resetting the iterator,
+C<values @array> in list context is no different to plain C<@array>.
+We recommend that you use void context C<keys @array> for this, but reasoned
+that it taking C<values @array> out would require more documentation than
+leaving it in.)
+
Note that the values are not copied, which means modifying them will
modify the contents of the hash:
projects / p5sagit/p5-mst-13.2.git / blobdiff