Ralf S. Engelschall > slice > IO::Handle

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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");
    }

    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

A IO::Handle object is a reference to a symbol (see the Symbol package)

CONSTRUCTOR ^

new ()

Creates a new IO::Handle object.

new_from_fd ( FD, MODE )

Creates a 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:

    close
    fileno
    getc
    eof
    read
    truncate
    stat
    print
    printf
    sysread
    syswrite

See perlvar for complete descriptions of each of the following supported IO::Handle methods:

    autoflush
    output_field_separator
    output_record_separator
    input_record_separator
    input_line_number
    format_page_number
    format_lines_per_page
    format_lines_left
    format_name
    format_top_name
    format_line_break_characters
    format_formfeed
    format_write

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, a IO::Handle object, or a file descriptor number.

$io->opened

Returns true if the object is currently a valid file descriptor.

$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 an array context but still returns just one line.

$io->getlines

This works like <$io> when called in an array 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.

$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->flush

Flush the given handle's buffer.

$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.

$io->clearerr

Clear the given handle's error indicator.

$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, 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. 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.

$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. 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! Note that you need to import the constants _IOFBF, _IOLBF, and _IONBF explicitly.

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.

NOTE ^

A IO::Handle object is a GLOB reference. 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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