IO::Handle(3) Perl Programmers Reference Guide IO::Handle(3)NAMEIO::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");
}
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 hierar
chy.
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 a "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 the perlfunc manpage 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->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 the perlvar manpage 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-filehan
dle 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, a 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 the I/O Operators
entry in the perlop manpage except that it's more
readable and can be safely called in a list context
but still returns just one line.
$io->getlines
This works like <$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 acciden
tally 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 experi
enced 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 out
standing 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 plat
forms. 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.
$io->blocking ( [ BOOL ] )
If called with an argument "blocking" will turn on
non-blocking IO if "BOOL" is false, and turn it off if
"BOOL" is true.
"blocking" will return the value of the previous set
ting, or the current setting if "BOOL" is not given.
If an error occurs "blocking" will return undef and
"$!" will be set.
If the C functions setbuf() and/or setvbuf() are avail
able, 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 parame
ter specifies a scalar variable to use as a buffer. You
should only change the buffer before any I/O, or immedi
ately after calling flush.
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 termina
tion, 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, set
buf returns nothing. setvbuf returns "0 but true", on suc
cess, "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 appropri
ate 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
A "IO::Handle" object is a reference to a symbol/GLOB ref
erence (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 pro
pose 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
the perlfunc manpage, the I/O Operators entry in the per
lop manpage, the IO::File manpage
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>
2001-03-18 perl v5.6.1 IO::Handle(3)
