IO::Handle
IO::Handle(3) Perl Programmers Reference Guide IO::Handle(3)
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 parame-
ters, 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 sup-
ported "IO::Handle" methods, which are just front ends for the corre-
sponding built-in functions:
$io->close
$io->eof
$io->fileno
$io->format_write( [FORMAT_NAME] )
$io->getc
$io->read ( BUF, LEN, [OFFSET] )
$io->print ( ARGS )
$io->printf ( FMT, [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 sup-
ported "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 parame-
ter is not a filename but rather a file handle name, an IO::Handle
object, or a file descriptor number.
$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 condi-
tional +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 oppo-
site 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.
$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 pol-
icy 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>
perl v5.8.8 2001-09-21 IO::Handle(3)
