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

       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;

           $io = new IO::Handle;
           if ($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;

       "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 hierar-

       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.

       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.

       See perlfunc for complete descriptions of each of the fol-
       lowing 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->format_write( [FORMAT_NAME] )
           $io->read ( BUF, LEN, [OFFSET] )
           $io->print ( ARGS )
           $io->printf ( FMT, [ARGS] )
           $io->sysread ( BUF, LEN, [OFFSET] )
           $io->syswrite ( BUF, [LEN, [OFFSET]] )
           $io->truncate ( LEN )

       See perlvar for complete descriptions of each of the fol-
       lowing 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

           $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-filehan-
       dle 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 descrip-
           tor number.

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

           This works like <$io> described in "I/O Operators" in
           perlop except that it's more readable and can be

perl v5.8.5                 2002-11-06                          2

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

           safely called in a list context but still returns just
           one line.

           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 acciden-
           tally 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 char-
           acter 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".

           Returns a true value if the given handle has experi-
           enced 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 out-
           standing errors.

           Clear the given handle's error indicator. Returns -1
           if the handle is invalid, 0 otherwise.

           "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 plat-
           forms. Returns "0 but true" on success, "undef" on
           error, "undef" for an invalid handle. See fsync(3c).

           "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.

perl v5.8.5                 2002-11-06                          3

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

       $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 set-
           ting, 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 avail-
       able, 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 parame-
       ter specifies a scalar variable to use as a buffer. You
       should only change the buffer before any I/O, or immedi-
       ately 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 termina-
       tion, 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, set-
       buf returns nothing. setvbuf returns "0 but true", on suc-
       cess, "undef" on failure.

       Lastly, there is a special method for working under -T and
       setuid/gid scripts:

           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 appropri-
           ate 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 "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

perl v5.8.5                 2002-11-06                          4

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

       variables in the hash table part of the GLOB. In an
       attempt to prevent modules trampling on each other I pro-
       pose 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

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

       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.

       Derived from FileHandle.pm by Graham Barr

perl v5.8.5                 2002-11-06                          5