


IO::Handle(3p)   Perl Programmers Reference Guide  IO::Handle(3p)


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:







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IO::Handle(3p)   Perl Programmers Reference Guide  IO::Handle(3p)


           $io->close
           $io->eof
           $io->fcntl( FUNCTION, SCALAR )
           $io->fileno
           $io->format_write( [FORMAT_NAME] )
           $io->getc
           $io->ioctl( FUNCTION, SCALAR )
           $io->read ( BUF, LEN, [OFFSET] )
           $io->print ( ARGS )
           $io->printf ( FMT, [ARGS] )
           $io->say ( 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.  (For the documentation of the
           "open" method, see IO::File.)

       $io->opened
           Returns true if the object is currently a valid file
           descriptor, false otherwise.



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IO::Handle(3p)   Perl Programmers Reference Guide  IO::Handle(3p)


       $io->getline
           This works like <$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.  If used as the conditional +within a
           "while" or C-style "for" loop, however, you will need
           to +emulate the functionality of <$io> with
           "defined($_ = $io->getline)".

       $io->getlines
           This works like <$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.



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IO::Handle(3p)   Perl Programmers Reference Guide  IO::Handle(3p)


       $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.



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IO::Handle(3p)   Perl Programmers Reference Guide  IO::Handle(3p)


           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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