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");
    }

    # 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;

CWIO::Handle is the base class for all other IO handle classes. It is not intended that objects of CWIO::Handle would be created directly, but instead CWIO::Handle is inherited from by several other classes in the IO hierarchy.

If you are reading this documentation, looking for a replacement for the CWFileHandle package, then I suggest you read the documentation for CWIO::File too.

new ()

Creates a new CWIO::Handle object.

new_from_fd ( FD, MODE )

Creates an CWIO::Handle like CWnew does. It requires two parameters, which are passed to the method CWfdopen; if the fdopen fails, the object is destroyed. Otherwise, it is returned to the caller.

See perlfunc for complete descriptions of each of the following supported CWIO::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 CWIO::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 CW$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 )

CWfdopen is like an ordinary CWopen 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 CWwrite is like CWwrite found in C, that is it is the opposite of read. The wrapper for the perl CWwrite function is called CWformat_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 CWclearerr, 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

CWsync synchronizes a file's in-memory state with that on the physical medium. CWsync 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. CWsync is not implemented on all platforms. Returns 0 but true on success, CWundef on error, CWundef for an invalid handle. See fsync(3c).

$io->flush

CWflush 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, CWundef on error.

$io->printflush ( ARGS )

Turns on autoflush, print ARGS and then restores the autoflush status of the CWIO::Handle object. Returns the return value from print.

$io->blocking ( [ BOOL ] )

If called with an argument CWblocking will turn on non-blocking IO if CWBOOL is false, and turn it off if CWBOOL is true. CWblocking will return the value of the previous setting, or the current setting if CWBOOL is not given. If an error occurs CWblocking will return undef and CW$! will be set.

If the C functions setbuf() and/or setvbuf() are available, then CWIO::Handle::setbuf and CWIO::Handle::setvbuf set the buffering policy for an IO::Handle. The calling sequences for the Perl functions are the same as their C counterpartsincluding the constants CW_IOFBF, CW_IOLBF, and CW_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 CWsetbuf or CWsetvbuf must not be modified in any way until the IO::Handle is closed or CWsetbuf or CWsetvbuf 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 CW_IOFBF, CW_IOLBF, and CW_IONBF explicitly. Like C, setbuf returns nothing. setvbuf returns 0 but true, on success, CWundef 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)

An CWIO::Handle object is a reference to a symbol/GLOB reference (see the CWSymbol package). Some modules that inherit from CWIO::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 CWtimeout variable in 'io_socket_timeout'.

perlfunc, I/O Operators in perlop, IO::File

Due to backwards compatibility, all filehandles resemble objects of class CWIO::Handle, or actually classes derived from that class. They actually aren't. Which means you can't derive your own class from CWIO::Handle and inherit those methods.

Derived from FileHandle.pm by Graham Barr <gbarr@pobox.com>