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man : IO::Handle(3p)
IO::Handle(3p) Perl Programmers Reference Guide IO::Handle(3p)
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 $io; # automatically closes the file if it's open
autoflush STDOUT 1;
DESCRIPTION
"IO::Handle" is the base class for all other IO handle
classes. It is not intended that objects of "IO::Handle"
would be created directly, but instead "IO::Handle" is
inherited from by several other classes in the IO
hierarchy.
If you are reading this documentation, looking for a
replacement for the "FileHandle" package, then I suggest
you read the documentation for "IO::File" too.
CONSTRUCTOR
new ()
Creates a new "IO::Handle" object.
new_from_fd ( FD, MODE )
Creates an "IO::Handle" like "new" does. It requires
two parameters, which are passed to the method
"fdopen"; if the fdopen fails, the object is
destroyed. Otherwise, it is returned to the caller.
METHODS
See perlfunc for complete descriptions of each of the
following supported "IO::Handle" methods, which are just
front ends for the corresponding built-in functions:
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$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->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.
$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
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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 like "write" found in C, that is it is
the opposite 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).
$io->flush
"flush" causes perl to flush any buffered data at the
perlio api level. Any unread data in the buffer will
be discarded, and any unwritten data will be written
to the underlying file descriptor. Returns "0 but
true" on success, "undef" on error.
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$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.
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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
<gbarrATpobox.com>
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