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IO::Handle(3pm)        Perl Programmers Reference Guide        IO::Handle(3pm)
NAME
       IO::Handle - supply object methods for I/O handles
SYNOPSIS
           use IO::Handle;
           $io = IO::Handle->new();
           if ($io->fdopen(fileno(STDIN),"r")) {
               print $io->getline;
               $io->close;
           }
           $io = IO::Handle->new();
           if ($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:
           $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.
       $io->getline
           This works like <$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 somewhat like "write" found in C, in that it is the
           opposite of read. The wrapper for the perl "write" function is
           called "format_write". However, whilst the C "write" function
           returns the number of bytes written, this "write" function simply
           returns true if successful (like "print"). A more C-like "write" is
           "syswrite" (see above).
       $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.
       $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. 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 AT pobox.com>
perl v5.26.3                      2018-03-01                   IO::Handle(3pm)