MirBSD manpage: IO::Handle(3p)

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 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.


     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:

perl v5.8.8                2005-02-05                           1

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 follow-
     ing 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

         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 han-
         dle name, an IO::Handle object, or a file descriptor

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

         This works like <$io> described in "I/O Operators" in

perl v5.8.8                2005-02-05                           2

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

         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 <$io> with "defined($_ =

         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 charac-
         ter 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 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.

         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 platforms. 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 suc-
         cess, "undef" on error.

perl v5.8.8                2005-02-05                           3

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 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 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:

         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 vulnera-
         bility should be kept in mind. Returns 0 on success, -1

perl v5.8.8                2005-02-05                           4

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

         if setting the taint-clean flag failed. (eg invalid han-


     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'.


     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 <gbarr@pobox.com>

perl v5.8.8                2005-02-05                           5

Generated on 2022-12-24 01:00:14 by $MirOS: src/scripts/roff2htm,v 1.113 2022/12/21 23:14:31 tg Exp $ — This product includes material provided by mirabilos.

These manual pages and other documentation are copyrighted by their respective writers; their sources are available at the project’s CVSweb, AnonCVS and other mirrors. The rest is Copyright © 2002–2022 MirBSD.

This manual page’s HTML representation is supposed to be valid XHTML/1.1; if not, please send a bug report — diffs preferred.

Kontakt / Impressum & Datenschutzerklärung