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@pobox.com>