IO::Handle

Section: Perl Programmers Reference Guide (3)
Updated: perl 5.004, patch 55
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NAME

IO::Handle - supply object methods for I/O handles

SYNOPSIS

    use IO::Handle;

    $fh = new IO::Handle;
    if ($fh->fdopen(fileno(STDIN),"r")) {
        print $fh->getline;
        $fh->close;
    }

    $fh = new IO::Handle;
    if ($fh->fdopen(fileno(STDOUT),"w")) {
        $fh->print("Some text\n");
    }

    use IO::Handle '_IOLBF';
    $fh->setvbuf($buffer_var, _IOLBF, 1024);

    undef $fh;       # 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 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:

    close
    fileno
    getc
    eof
    read
    truncate
    stat
    print
    printf
    sysread
    syswrite

See the perlvar manpage 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:

$fh->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.
$fh->opened: Returns true if the object is currently a valid file descriptor.
$fh->getline: This works like <$fh> described in the section on I/O Operators in the perlop manpage except that it's more readable and can be safely called in an array context but still returns just one line.
$fh->getlines: This works like <$fh> 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.
$fh->ungetc ( ORD ): Pushes a character with the given ordinal value back onto the given handle's input stream.
$fh->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.
$fh->flush: Flush the given handle's buffer.
$fh->error: Returns a true value if the given handle has experienced any errors since it was opened or since the last call to clearerr.
$fh->clearerr: Clear the given handle's error indicator.

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:

$fh->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'.

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 <bodg@tiuk.ti.com>

This document was created by man2html, using the manual pages.
Time: 23:58:16 GMT, February 15, 2023