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IO::Handle(3)
NAME
IO::Handle - supply object methods for I/O handles
SYNOPSIS
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");
}
# setvbuf is not available by default on Perls 5.8.0 and later.
use IO::Handle '_IOLBF';
$io->setvbuf($buffer_var, _IOLBF, 1024);
undef $io; # automatically closes the file if it's open
autoflush STDOUT 1;
DESCRIPTION
"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.
CONSTRUCTOR
new ()
Creates a new "IO::Handle" object.
new_from_fd ( FD, MODE )
Creates an "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.
METHODS
See perlfunc 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 perlvar 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:
$io->fdopen ( FD, MODE )
"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.
$io->opened
Returns true if the object is currently a valid file descriptor, false
otherwise.
$io->getline
This works like <$io> described in "I/O Operators" in perlop except
that it's more readable and can be safely called in a list context but
still returns just one line.
$io->getlines
This works like <$io> when called in a list context to read all the
remaining lines in a file, except that it's more readable. It will
also croak() if accidentally called in a scalar context.
$io->ungetc ( ORD )
Pushes a character with the given ordinal value back onto the given
handle's input stream. Only one character of pushback per handle is
guaranteed.
$io->write ( BUF, LEN [, OFFSET ] )
This "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".
$io->error
Returns a true value if the given handle has experienced any errors
since it was opened or since the last call to "clearerr", or if the
handle is invalid. It only returns false for a valid handle with no
outstanding errors.
$io->clearerr
Clear the given handle's error indicator. Returns -1 if the handle is
invalid, 0 otherwise.
$io->sync
"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).
$io->flush
"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->printflush ( ARGS )
Turns on autoflush, print ARGS and then restores the autoflush status
of the "IO::Handle" object. Returns the return value from print.
$io->blocking ( [ BOOL ] )
If called with an argument "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: The IO::Handle::setvbuf() is not available by default on Perls
5.8.0 and later because setvbuf() is rather specific to using the stdio
library, while Perl prefers the new perlio subsystem instead.
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:
$io->untaint
Marks the object as taint-clean, and as such data read from it will
also be considered taint-clean. Note that this is a very trusting
action to take, and appropriate consideration for the data source and
potential vulnerability should be kept in mind. Returns 0 on success,
-1 if setting the taint-clean flag failed. (eg invalid handle)
NOTE
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'.
SEE ALSO
perlfunc, "I/O Operators" in perlop, IO::File
BUGS
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.
HISTORY
Derived from FileHandle.pm by Graham Barr <gbarr@pobox.com>
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