=item Functions new in perl5
C<abs>, C<bless>, C<chomp>, C<chr>, C<exists>, C<formline>, C<glob>,
-C<import>, C<lc>, C<lcfirst>, C<map>, C<my>, C<no>, C<our>, C<prototype>,
+C<import>, C<lc>, C<lcfirst>, C<map>, C<my>, C<no>, C<our>, C<prototype>,
C<qx>, C<qw>, C<readline>, C<readpipe>, C<ref>, C<sub*>, C<sysopen>, C<tie>,
C<tied>, C<uc>, C<ucfirst>, C<untie>, C<use>
Be aware that the optimizer might have optimized call frames away before
C<caller> had a chance to get the information. That means that C<caller(N)>
might not return information about the call frame you expect it do, for
-C<< N > 1 >>. In particular, C<@DB::args> might have information from the
+C<< N > 1 >>. In particular, C<@DB::args> might have information from the
previous time C<caller> was called.
=item chdir EXPR
mode (C<$/ = "">), it removes all trailing newlines from the string.
When in slurp mode (C<$/ = undef>) or fixed-length record mode (C<$/> is
a reference to an integer or the like, see L<perlvar>) chomp() won't
-remove anything.
+remove anything.
If VARIABLE is omitted, it chomps C<$_>. Example:
while (<>) {
Returns the character represented by that NUMBER in the character set.
For example, C<chr(65)> is C<"A"> in either ASCII or Unicode, and
-chr(0x263a) is a Unicode smiley face. Within the scope of C<use utf8>,
+chr(0x263a) is a Unicode smiley face. Within the scope of C<use utf8>,
characters higher than 127 are encoded in Unicode; if you don't want
this, temporarily C<use bytes> or use C<pack("C*",...)>
-For the reverse, use L</ord>.
+For the reverse, use L</ord>.
See L<utf8> for more about Unicode.
If NUMBER is omitted, uses C<$_>.
If the file handle came from a piped open C<close> will additionally
return false if one of the other system calls involved fails or if the
program exits with non-zero status. (If the only problem was that the
-program exited non-zero C<$!> will be set to C<0>.) Closing a pipe
+program exited non-zero C<$!> will be set to C<0>.) Closing a pipe
also waits for the process executing on the pipe to complete, in case you
-want to look at the output of the pipe afterwards, and
+want to look at the output of the pipe afterwards, and
implicitly puts the exit status value of that command into C<$?>.
Prematurely closing the read end of a pipe (i.e. before the process
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
+the size of the array will shrink to the highest element that tests
true for exists() (or 0 if no such element exists).
Returns each element so deleted or the undefined value if there was no such
as the first line of the handler (see L<perlvar/$^S>). Because
this promotes strange action at a distance, this counterintuitive
-behavior may be fixed in a future release.
+behavior may be fixed in a future release.
=item do BLOCK
You might like to use C<do> to read in a program configuration
file. Manual error checking can be done this way:
- # read in config files: system first, then user
+ # read in config files: system first, then user
for $file ("/share/prog/defaults.rc",
- "$ENV{HOME}/.someprogrc")
+ "$ENV{HOME}/.someprogrc")
{
unless ($return = do $file) {
warn "couldn't parse $file: $@" if $@;
B<WARNING>: Any files opened at the time of the dump will I<not>
be open any more when the program is reincarnated, with possible
-resulting confusion on the part of Perl.
+resulting confusion on the part of Perl.
This function is now largely obsolete, partly because it's very
hard to convert a core file into an executable, and because the
you're just trying to accelerate a CGI script, consider using the
C<mod_perl> extension to B<Apache>, or the CPAN module, Fast::CGI.
You might also consider autoloading or selfloading, which at least
-make your program I<appear> to run faster.
+make your program I<appear> to run faster.
=item each HASH
# reset line numbering on each input file
while (<>) {
- next if /^\s*#/; # skip comments
+ next if /^\s*#/; # skip comments
print "$.\t$_";
} continue {
close ARGV if eof; # Not eof()!
the entire argument is passed to the system's command shell for parsing
(this is C</bin/sh -c> on Unix platforms, but varies on other platforms).
If there are no shell metacharacters in the argument, it is split into
-words and passed directly to C<execvp>, which is more efficient.
+words and passed directly to C<execvp>, which is more efficient.
Examples:
exec '/bin/echo', 'Your arguments are: ', @ARGV;
=item exp
-Returns I<e> (the natural logarithm base) to the power of EXPR.
+Returns I<e> (the natural logarithm base) to the power of EXPR.
If EXPR is omitted, gives C<exp($_)>.
=item fcntl FILEHANDLE,FUNCTION,SCALAR
use Fcntl;
first to get the correct constant definitions. Argument processing and
-value return works just like C<ioctl> below.
+value return works just like C<ioctl> below.
For example:
use Fcntl;
If FILEHANDLE is an expression, the value is taken as an indirect
filehandle, generally its name.
-You can use this to find out whether two handles refer to the
+You can use this to find out whether two handles refer to the
same underlying descriptor:
if (fileno(THIS) == fileno(THAT)) {
print "THIS and THAT are dups\n";
- }
+ }
+
+(Filehandles connected to memory objects via new features of C<open> may
+return undefined even though they are open.)
+
=item flock FILEHANDLE,OPERATION
use User::pwent;
$is_his = (stat($filename)->uid == pwent($whoever)->uid);
-Even though it looks like they're the same method calls (uid),
-they aren't, because a C<File::stat> object is different from
+Even though it looks like they're the same method calls (uid),
+they aren't, because a C<File::stat> object is different from
a C<User::pwent> object.
=item getsockname SOCKET
use Socket;
$mysockaddr = getsockname(SOCK);
($port, $myaddr) = sockaddr_in($mysockaddr);
- printf "Connect to %s [%s]\n",
+ printf "Connect to %s [%s]\n",
scalar gethostbyaddr($myaddr, AF_INET),
inet_ntoa($myaddr);
with the time localized for the standard Greenwich time zone.
Typically used as follows:
- # 0 1 2 3 4 5 6 7
+ # 0 1 2 3 4 5 6 7
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday) =
gmtime(time);
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.)
+the year, in the range C<0..364> (or C<0..365> in leap years.)
Note that the $year element is I<not> simply the last two digits of
the year. If you assume it is, then you create non-Y2K-compliant
passed rather than a pointer to the string value. To guarantee this to be
true, add a C<0> to the scalar before using it.) The C<pack> and C<unpack>
functions may be needed to manipulate the values of structures used by
-C<ioctl>.
+C<ioctl>.
The return value of C<ioctl> (and C<fcntl>) is as follows:
@keys = keys %ENV;
@values = values %ENV;
- while (@keys) {
+ while (@keys) {
print pop(@keys), '=', pop(@values), "\n";
}
=item length
Returns the length in characters of the value of EXPR. If EXPR is
-omitted, returns length of C<$_>. Note that this cannot be used on
+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.
=item link OLDFILE,NEWFILE
Creates a new filename linked to the old filename. Returns true for
-success, false otherwise.
+success, false otherwise.
=item listen SOCKET,QUEUESIZE
Does the same thing that the listen system call does. Returns true if
-it succeeded, false otherwise. See the example in
+it succeeded, false otherwise. See the example in
L<perlipc/"Sockets: Client/Server Communication">.
=item local EXPR
You really probably want to be using C<my> instead, because C<local> isn't
-what most people think of as "local". See
+what most people think of as "local". See
L<perlsub/"Private Variables via my()"> for details.
A local modifies the listed variables to be local to the enclosing
sub log10 {
my $n = shift;
return log($n)/log(10);
- }
+ }
See also L</exp> for the inverse operation.
If MODE is C<< '<' >> or nothing, the file is opened for input.
If MODE is C<< '>' >>, the file is truncated and opened for
output, being created if necessary. If MODE is C<<< '>>' >>>,
-the file is opened for appending, again being created if necessary.
+the file is opened for appending, again being created if necessary.
You can put a C<'+'> in front of the C<< '>' >> or C<< '<' >> to indicate that
you want both read and write access to the file; thus C<< '+<' >> is almost
always preferred for read/write updates--the C<< '+>' >> mode would clobber the
and L<perlipc/"Bidirectional Communication"> for alternatives.)
In the 2-arguments (and 1-argument) form opening C<'-'> opens STDIN
-and opening C<< '>-' >> opens STDOUT.
+and opening C<< '>-' >> opens STDOUT.
Open returns
nonzero upon success, the undefined value otherwise. If the C<open>
the return value from opening a file. The infrequent exception is when
working with an unopened filehandle is actually what you want to do.
+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 ...
+
+opens a filehandle to an anonymous temporary file.
+
Examples:
$ARTICLE = 100;
C<< < >>, C<< +> >>, C<<< +>> >>>, and C<< +< >>. The
mode you specify should match the mode of the original filehandle.
(Duping a filehandle does not take into account any existing contents of
-stdio buffers.) Duping file handles is not yet supported for 3-argument
-open().
+stdio buffers.) If you use the 3 arg form then you can pass either a number,
+the name of a filehandle or the normal "reference to a glob".
Here is a script that saves, redirects, and restores STDOUT and
STDERR:
#!/usr/bin/perl
- open(OLDOUT, ">&STDOUT");
+ open(my $oldout, ">&", \*STDOUT);
open(OLDERR, ">&STDERR");
open(STDOUT, '>', "foo.out") || die "Can't redirect stdout";
parsimonious of file descriptors. For example:
open(FILEHANDLE, "<&=$fd")
+or
+ open(FILEHANDLE, "<&=", $fd)
-Note that this feature depends on the fdopen() C library function.
-On many UNIX systems, fdopen() is known to fail when file descriptors
+Note that if perl is using the standard C libaries fdopen() then on many UNIX systems,
+fdopen() is known to fail when file descriptors
exceed a certain value, typically 255. If you need more file
-descriptors than that, consider rebuilding Perl to use the C<sfio>
-library.
+descriptors than that, consider rebuilding Perl to use the C<PerlIO>.
If you open a pipe on the command C<'-'>, i.e., either C<'|-'> or C<'-|'>
with 2-arguments (or 1-argument) form of open(), then
open(FOO, "|tr '[a-z]' '[A-Z]'");
open(FOO, '|-', "tr '[a-z]' '[A-Z]'");
open(FOO, '|-') || exec 'tr', '[a-z]', '[A-Z]';
+ open(FOO, '|-', "tr", '[a-z]', '[A-Z]');
open(FOO, "cat -n '$file'|");
open(FOO, '-|', "cat -n '$file'");
open(FOO, '-|') || exec 'cat', '-n', $file;
+ open(FOO, '-|', "cat", '-n', $file);
+
+The last example in each block shows the pipe as "list form", which is
+not yet supported on all platforms.
See L<perlipc/"Safe Pipe Opens"> for more examples of this.
The filename passed to 2-argument (or 1-argument) form of open()
will have leading and trailing
whitespace deleted, and the normal redirection characters
-honored. This property, known as "magic open",
+honored. This property, known as "magic open",
can often be used to good effect. A user could specify a filename of
F<"rsh cat file |">, or you could change certain filenames as needed:
print $Config{longlongsize}, "\n";
(The C<$Config{longlongsize}> will be undefine if your system does
-not support long longs.)
+not support long longs.)
=item *
=item package NAMESPACE
-=item package
+=item package
Declares the compilation unit as being in the given namespace. The scope
of the package declaration is from the declaration itself through the end
}
if (UNIVERSAL::isa($r, "HASH")) { # for subclassing
print "r is a reference to something that isa hash.\n";
- }
+ }
See also L<perlref>.
In other words, if you try this:
- require Foo::Bar; # a splendid bareword
+ require Foo::Bar; # a splendid bareword
-The require function will actually look for the "F<Foo/Bar.pm>" file in the
+The require function will actually look for the "F<Foo/Bar.pm>" file in the
directories specified in the C<@INC> array.
But if you try this:
#or
require "Foo::Bar"; # not a bareword because of the ""
-The require function will look for the "F<Foo::Bar>" file in the @INC array and
+The require function will look for the "F<Foo::Bar>" file in the @INC array and
will complain about not finding "F<Foo::Bar>" there. In this case you can do:
eval "require $class";
=item return
-Returns from a subroutine, C<eval>, or C<do FILE> with the value
+Returns from a subroutine, C<eval>, or C<do FILE> with the value
given in EXPR. Evaluation of EXPR may be in list, scalar, or void
context, depending on how the return value will be used, and the context
may vary from one execution to the next (see C<wantarray>). If no EXPR
This is useful with sockets when you want to tell the other
side you're done writing but not done reading, or vice versa.
-It's also a more insistent form of close because it also
+It's also a more insistent form of close because it also
disables the file descriptor in any forked copies in other
processes.
%b an unsigned integer, in binary
%p a pointer (outputs the Perl value's address in hexadecimal)
%n special: *stores* the number of characters output so far
- into the next variable in the parameter list
+ into the next variable in the parameter list
Finally, for backward (and we do mean "backward") compatibility, Perl
permits these unnecessary but widely-supported conversions:
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">
+should mask off the file type portion and (s)printf using a C<"%o">
if you want to see the real permissions.
$mode = (stat($filename))[2];
use File::stat;
$sb = stat($filename);
- printf "File is %s, size is %s, perm %04o, mtime %s\n",
+ printf "File is %s, size is %s, perm %04o, mtime %s\n",
$filename, $sb->size, $sb->mode & 07777,
scalar localtime $sb->mtime;
and the setuid/setgid/sticky bits
S_IFMT($mode) the part of $mode containing the file type
- which can be bit-anded with e.g. S_IFREG
+ which can be bit-anded with e.g. S_IFREG
or with the following functions
# The operators -f, -d, -l, -b, -c, -p, and -s.
There's a problem with C<syscall(&SYS_pipe)>: it returns the file
number of the read end of the pipe it creates. There is no way
-to retrieve the file number of the other end. You can avoid this
+to retrieve the file number of the other end. You can avoid this
problem by using C<pipe> instead.
=item sysopen FILEHANDLE,FILENAME,MODE
Returns the current position for FILEHANDLE, or -1 on error. FILEHANDLE
may be an expression whose value gives the name of the actual filehandle.
-If FILEHANDLE is omitted, assumes the file last read.
+If FILEHANDLE is omitted, assumes the file last read.
The return value of tell() for the standard streams like the STDIN
depends on the operating system: it may return -1 or something else.
If the repeat count of a field is larger than what the remainder of
the input string allows, repeat count is decreased. If the input string
-is longer than one described by the TEMPLATE, the rest is ignored.
+is longer than one described by the TEMPLATE, the rest is ignored.
See L</pack> for more examples and notes.
C<use> will call the VERSION method in class Module with the given
version as an argument. The default VERSION method, inherited from
the UNIVERSAL class, croaks if the given version is larger than the
-value of the variable C<$Module::VERSION>.
+value of the variable C<$Module::VERSION>.
Again, there is a distinction between omitting LIST (C<import> called
with no arguments) and an explicit empty LIST C<()> (C<import> not
be a power of two from 1 to 32 (or 64, if your platform supports
that).
-If BITS is 8, "elements" coincide with bytes of the input string.
+If BITS is 8, "elements" coincide with bytes of the input string.
If BITS is 16 or more, bytes of the input string are grouped into chunks
of size BITS/8, and each group is converted to a number as with
#!/usr/bin/perl -wl
print <<'EOT';
- 0 1 2 3
+ 0 1 2 3
unpack("V",$_) 01234567890123456789012345678901
------------------------------------------------------------------
EOT
Regardless of the machine architecture on which it is run, the above
example should print the following table:
- 0 1 2 3
+ 0 1 2 3
unpack("V",$_) 01234567890123456789012345678901
------------------------------------------------------------------
vec($_, 0, 1) = 1 == 1 10000000000000000000000000000000
use POSIX ":sys_wait_h";
#...
- do {
+ do {
$kid = waitpid(-1,&WNOHANG);
} until $kid == -1;
fixed, and are defined by the C<PerlIO_funcs> type. They are broadly the
same as the public C<PerlIO_xxxxx> functions:
- struct _PerlIO_funcs
- {
- char * name;
- Size_t size;
- IV kind;
- IV (*Fileno)(PerlIO *f);
- PerlIO * (*Fdopen)(PerlIO_funcs *tab, int fd, const char *mode);
- PerlIO * (*Open)(PerlIO_funcs *tab, const char *path, const char *mode);
- int (*Reopen)(const char *path, const char *mode, PerlIO *f);
- IV (*Pushed)(PerlIO *f,const char *mode,const char *arg,STRLEN len);
- IV (*Popped)(PerlIO *f);
- /* Unix-like functions - cf sfio line disciplines */
- SSize_t (*Read)(PerlIO *f, void *vbuf, Size_t count);
- SSize_t (*Unread)(PerlIO *f, const void *vbuf, Size_t count);
- SSize_t (*Write)(PerlIO *f, const void *vbuf, Size_t count);
- IV (*Seek)(PerlIO *f, Off_t offset, int whence);
- Off_t (*Tell)(PerlIO *f);
- IV (*Close)(PerlIO *f);
- /* Stdio-like buffered IO functions */
- IV (*Flush)(PerlIO *f);
- IV (*Fill)(PerlIO *f);
- IV (*Eof)(PerlIO *f);
- IV (*Error)(PerlIO *f);
- void (*Clearerr)(PerlIO *f);
- void (*Setlinebuf)(PerlIO *f);
- /* Perl's snooping functions */
- STDCHAR * (*Get_base)(PerlIO *f);
- Size_t (*Get_bufsiz)(PerlIO *f);
- STDCHAR * (*Get_ptr)(PerlIO *f);
- SSize_t (*Get_cnt)(PerlIO *f);
- void (*Set_ptrcnt)(PerlIO *f,STDCHAR *ptr,SSize_t cnt);
- };
+ struct _PerlIO_funcs
+ {
+ char * name;
+ Size_t size;
+ IV kind;
+ IV (*Pushed)(PerlIO *f,const char *mode,SV *arg);
+ IV (*Popped)(PerlIO *f);
+ PerlIO * (*Open)(pTHX_ PerlIO_funcs *tab,
+ AV *layers, IV n,
+ const char *mode,
+ int fd, int imode, int perm,
+ PerlIO *old,
+ int narg, SV **args);
+ SV * (*Getarg)(PerlIO *f);
+ IV (*Fileno)(PerlIO *f);
+ /* Unix-like functions - cf sfio line disciplines */
+ SSize_t (*Read)(PerlIO *f, void *vbuf, Size_t count);
+ SSize_t (*Unread)(PerlIO *f, const void *vbuf, Size_t count);
+ SSize_t (*Write)(PerlIO *f, const void *vbuf, Size_t count);
+ IV (*Seek)(PerlIO *f, Off_t offset, int whence);
+ Off_t (*Tell)(PerlIO *f);
+ IV (*Close)(PerlIO *f);
+ /* Stdio-like buffered IO functions */
+ IV (*Flush)(PerlIO *f);
+ IV (*Fill)(PerlIO *f);
+ IV (*Eof)(PerlIO *f);
+ IV (*Error)(PerlIO *f);
+ void (*Clearerr)(PerlIO *f);
+ void (*Setlinebuf)(PerlIO *f);
+ /* Perl's snooping functions */
+ STDCHAR * (*Get_base)(PerlIO *f);
+ Size_t (*Get_bufsiz)(PerlIO *f);
+ STDCHAR * (*Get_ptr)(PerlIO *f);
+ SSize_t (*Get_cnt)(PerlIO *f);
+ void (*Set_ptrcnt)(PerlIO *f,STDCHAR *ptr,SSize_t cnt);
+ };
+
+
The first few members of the struct give a "name" for the layer, the
size to C<malloc> for the per-instance data, and some flags which are
=over 4
-=item IV (*Fileno)(PerlIO *f);
-
-Returns the Unix/Posix numeric file decriptor for the handle. Normally
-C<PerlIOBase_fileno()> (which just asks next layer down) will suffice
-for this.
+=item IV (*Pushed)(PerlIO *f,const char *mode, SV *arg);
-=item PerlIO * (*Fdopen)(PerlIO_funcs *tab, int fd, const char *mode);
-
-Should (perhaps indirectly) call C<PerlIO_allocate()> to allocate a slot
-in the table and associate it with the given numeric file descriptor,
-which will be open in an manner compatible with the supplied mode string.
-
-=item PerlIO * (*Open)(PerlIO_funcs *tab, const char *path, const char *mode);
-
-Should attempt to open the given path and if that succeeds then (perhaps
-indirectly) call C<PerlIO_allocate()> to allocate a slot in the table and
-associate it with the layers information for the opened file.
-
-=item int (*Reopen)(const char *path, const char *mode, PerlIO *f);
-
-Re-open the supplied C<PerlIO *> to connect it to C<path> in C<mode>.
-Returns as success flag. Perl does not use this and L<perlapio> marks it
-as subject to change.
-
-=item IV (*Pushed)(PerlIO *f,const char *mode,const char *arg,STRLEN len);
-
-Called when the layer is pushed onto the stack. The C<mode> argument may
-be NULL if this occurs post-open. The C<arg> and C<len> will be present
+The only absoultely mandatory method. Called when the layer is pushed onto the stack.
+The C<mode> argument may be NULL if this occurs post-open. The C<arg> will be non-C<NULL>
if an argument string was passed. In most cases this should call
C<PerlIOBase_pushed()> to convert C<mode> into the appropriate
C<PERLIO_F_XXXXX> flags in addition to any actions the layer itself takes.
+If a layer is not expecting an argument it need neither save the one passed to it, nor
+provide C<Getarg()> (it could perhaps C<Perl_warn> that the argument was un-expected).
=item IV (*Popped)(PerlIO *f);
closed if the program is dynamically managing layers on the stream. In
such cases C<Popped()> should free any resources (buffers, translation
tables, ...) not held directly in the layer's struct.
+It should also C<Unread()> any unconsumed data that has been read and buffered
+from the layer below back to that layer, so that it can be re-provided to what
+ever is now above.
+
+=item PerlIO * (*Open)(...);
+
+The C<Open()> method has lots of arguments because it combines the functions
+of perl's C<open>, C<PerlIO_open>, perl's C<sysopen>, C<PerlIO_fdopen> and C<PerlIO_reopen>.
+The full prototype is as follows:
+
+ PerlIO * (*Open)(pTHX_ PerlIO_funcs *tab,
+ AV *layers, IV n,
+ const char *mode,
+ int fd, int imode, int perm,
+ PerlIO *old,
+ int narg, SV **args);
+
+Open should (perhaps indirectly) call C<PerlIO_allocate()> to allocate a slot in the table and
+associate it with the layers information for the opened file, by calling C<PerlIO_push>.
+The I<layers> AV is an array of all the layers destined for the C<PerlIO *>,
+and any arguments passed to them, I<n> is the index into that array of the
+layer being called. The macro C<PerlIOArg> will return a (possibly C<NULL>) SV *
+for the argument passed to the layer.
+
+The I<mode> string is an "C<fopen()>-like" string which would match the regular
+expression C</^[I#]?[rwa]\+?[bt]?$/>.
+
+The C<'I'> prefix is used during creation of C<stdin>..C<stderr> via special
+C<PerlIO_fdopen> calls; the C<'#'> prefix means that this is C<sysopen> and that I<imode> and
+I<perm> should be passed to C<PerlLIO_open3>; C<'r'> means B<r>ead, C<'w'> means B<w>rite
+and C<'a'> means B<a>ppend. The C<'+'> suffix means that both reading and writing/appending
+are permited. The C<'b'> suffix means file should be binary, and C<'t'> means it
+is text. (Binary/Text should be ignored by almost all layers and binary IO done,
+with PerlIO. The C<:crlf> layer should be pushed to handle the distinction.)
+
+If I<old> is not C<NULL> then this is a C<PerlIO_reopen>. Perl iteself does not use
+this (yet?) and semantics are a little vague.
+
+If I<fd> not negative then it is the numeric file descriptor I<fd>, which will
+be open in an manner compatible with the supplied mode string, the call is
+thus equivalent to C<PerlIO_fdopen>. In this case I<nargs> will be zero.
+
+If I<nargs> is greater than zero then it gives the number of arguments passed
+to C<open>, otherwise it will be 1 if for example C<PerlIO_open> was called.
+In simple cases SvPV(*args) is the pathname to open.
+
+Having said all that translation-only layers do not need to provide C<Open()> at all,
+but rather leave the opening to a lower level layer and wait to be "pushed".
+If a layer does provide C<Open()> it should normaly call the C<Open()> method
+of next layer down (if any) and then push itself on top if that succeeds.
+
+=item SV * (*Getarg)(PerlIO *f);
+
+Optional. If present should return an SV * representing the string argument
+passed to the layer when it was pushed. e.g. ":encoding(ascii)" would
+return an SvPV with value "ascii".
+
+=item IV (*Fileno)(PerlIO *f);
+
+Returns the Unix/Posix numeric file decriptor for the handle. Normally
+C<PerlIOBase_fileno()> (which just asks next layer down) will suffice
+for this.
=item SSize_t (*Read)(PerlIO *f, void *vbuf, Size_t count);
Should make stream's state consistent with layers below. That is, any
buffered write data should be written, and file position of lower layers
adjusted for data read fron below but not actually consumed.
+(Should perhaps C<Unread()> such data to the lower layer.)
=item IV (*Fill)(PerlIO *f);
=item void (*Setlinebuf)(PerlIO *f);
-Mark the stream as line buffered.
+Mark the stream as line buffered. C<PerlIOBase_setlinebuf()> sets the
+PERLIO_F_LINEBUF flag and is normally sufficient.
=item STDCHAR * (*Get_base)(PerlIO *f);
=head2 Extension Layers
-Layers can made available by extension modules.
+Layers can made available by extension modules. When an unknown layer is encountered
+the PerlIO code will perform the equivalent of :
+
+ use PerlIO 'layer';
+
+Where I<layer> is the unknown layer. F<PerlIO.pm> will then attempt to :
+
+ require PerlIO::layer;
+
+If after that process the layer is still not defined then the C<open> will fail.
+
+The following extension layers are bundled with perl:
=over 4
-=item "encoding"
+=item ":encoding"
use Encoding;
-makes this layer available. It is an example of a layer which takes an argument.
-as it is called as:
+makes this layer available, although F<PerlIO.pm> "knows" where to find it.
+It is an example of a layer which takes an argument as it is called thus:
open($fh,"<:encoding(iso-8859-7)",$pathname)
-=back
+=item ":Scalar"
+
+Provides support for
+
+ open($fh,"...",\$scalar)
+When a handle is so opened, then reads get bytes from the string value of I<$scalar>,
+and writes change the value. In both cases the position in I<$scalar> starts as zero
+but can be altered via C<seek>, and determined via C<tell>.
+
+=item ":Object" or ":Perl"
+
+May be provided to allow layers to be implemented as perl code - implementation
+is being investigated.
+
+=back
=cut
projects / p5sagit/p5-mst-13.2.git / commitdiff