IO::Handle - supply object methods for I/O handles |
IO::Handle - supply object methods for I/O handles
use IO::Handle;
$io = new IO::Handle; if ($io->fdopen(fileno(STDIN),"r")) { print $io->getline; $io->close; }
$io = new IO::Handle; if ($io->fdopen(fileno(STDOUT),"w")) { $io->print("Some text\n"); }
use IO::Handle '_IOLBF'; $io->setvbuf($buffer_var, _IOLBF, 1024);
undef $io; # automatically closes the file if it's open
autoflush STDOUT 1;
IO::Handle
is the base class for all other IO handle classes. It is
not intended that objects of IO::Handle
would be created directly,
but instead IO::Handle
is inherited from by several other classes
in the IO hierarchy.
If you are reading this documentation, looking for a replacement for
the FileHandle
package, then I suggest you read the documentation
for IO::File
too.
IO::Handle
object.
IO::Handle
like new
does.
It requires two parameters, which are passed to the method fdopen
;
if the fdopen fails, the object is destroyed. Otherwise, it is returned
to the caller.
See the perlfunc manpage for complete descriptions of each of the following
supported IO::Handle
methods, which are just front ends for the
corresponding built-in functions:
$io->close $io->eof $io->fileno $io->format_write( [FORMAT_NAME] ) $io->getc $io->read ( BUF, LEN, [OFFSET] ) $io->print ( ARGS ) $io->printf ( FMT, [ARGS] ) $io->stat $io->sysread ( BUF, LEN, [OFFSET] ) $io->syswrite ( BUF, [LEN, [OFFSET]] ) $io->truncate ( LEN )
See the perlvar manpage for complete descriptions of each of the following
supported IO::Handle
methods. All of them return the previous
value of the attribute and takes an optional single argument that when
given will set the value. If no argument is given the previous value
is unchanged (except for $io->autoflush will actually turn ON
autoflush by default).
$io->autoflush ( [BOOL] ) $| $io->format_page_number( [NUM] ) $% $io->format_lines_per_page( [NUM] ) $= $io->format_lines_left( [NUM] ) $- $io->format_name( [STR] ) $~ $io->format_top_name( [STR] ) $^ $io->input_line_number( [NUM]) $.
The following methods are not supported on a per-filehandle basis.
IO::Handle->format_line_break_characters( [STR] ) $: IO::Handle->format_formfeed( [STR]) $^L IO::Handle->output_field_separator( [STR] ) $, IO::Handle->output_record_separator( [STR] ) $\
IO::Handle->input_record_separator( [STR] ) $/
Furthermore, for doing normal I/O you might need these:
fdopen
is like an ordinary open
except that its first parameter
is not a filename but rather a file handle name, an IO::Handle object,
or a file descriptor number.
croak()
if accidentally called in a scalar context.
write
is like write
found in C, that is it is the
opposite of read. The wrapper for the perl write
function is
called format_write
.
clearerr
, or if the
handle is invalid. It only returns false for a valid handle with no
outstanding errors.
sync
synchronizes a file's in-memory state with that on the
physical medium. sync
does not operate at the perlio api level, but
operates on the file descriptor (similar to sysread, sysseek and
systell). This means that any data held at the perlio api level will not
be synchronized. To synchronize data that is buffered at the perlio api
level you must use the flush method. sync
is not implemented on all
platforms. Returns ``0 but true'' on success, undef
on error, undef
for an invalid handle. See fsync(3c).
flush
causes perl to flush any buffered data at the perlio api level.
Any unread data in the buffer will be discarded, and any unwritten data
will be written to the underlying file descriptor. Returns ``0 but true''
on success, undef
on error.
IO::Handle
object. Returns the return value from print.
blocking
will turn on non-blocking IO if
BOOL
is false, and turn it off if BOOL
is true.
blocking
will return the value of the previous setting, or the
current setting if BOOL
is not given.
If an error occurs blocking
will return undef and $!
will be set.
If the C functions setbuf()
and/or setvbuf()
are available, then
IO::Handle::setbuf
and IO::Handle::setvbuf
set the buffering
policy for an IO::Handle. The calling sequences for the Perl functions
are the same as their C counterparts--including the constants _IOFBF
,
_IOLBF
, and _IONBF
for setvbuf()--except that the buffer parameter
specifies a scalar variable to use as a buffer. You should only
change the buffer before any I/O, or immediately after calling flush.
WARNING: A variable used as a buffer by setbuf
or setvbuf
must not
be modified in any way until the IO::Handle is closed or setbuf
or
setvbuf
is called again, or memory corruption may result! Remember that
the order of global destruction is undefined, so even if your buffer
variable remains in scope until program termination, it may be undefined
before the file IO::Handle is closed. Note that you need to import the
constants _IOFBF
, _IOLBF
, and _IONBF
explicitly. Like C, setbuf
returns nothing. setvbuf returns ``0 but true'', on success, undef
on
failure.
Lastly, there is a special method for working under -T and setuid/gid scripts:
An IO::Handle
object is a reference to a symbol/GLOB reference (see
the Symbol
package). Some modules that
inherit from IO::Handle
may want to keep object related variables
in the hash table part of the GLOB. In an attempt to prevent modules
trampling on each other I propose the that any such module should prefix
its variables with its own name separated by _'s. For example the IO::Socket
module keeps a timeout
variable in 'io_socket_timeout'.
the perlfunc manpage, I/O Operators in the perlop manpage, the IO::File manpage
Due to backwards compatibility, all filehandles resemble objects
of class IO::Handle
, or actually classes derived from that class.
They actually aren't. Which means you can't derive your own
class from IO::Handle
and inherit those methods.
Derived from FileHandle.pm by Graham Barr <gbarr@pobox.com>
IO::Handle - supply object methods for I/O handles |