IO::Handle(3pm) Perl Programmers Reference Guide IO::Handle(3pm)
NAME
IO::Handle - supply object methods for I/O handles
SYNOPSIS
use IO::Handle;
my $io = IO::Handle->new();
if ($io->fdopen(fileno(STDIN),"r")) {
print $io->getline;
$io->close;
}
my $io = IO::Handle->new();
if ($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(my $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(1), "I/O Operators" in perlop(1), IO::File(3)
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 v5.38.2 2023-11-28 IO::Handle(3pm)
perl 5.38.2 - Generated Sat Dec 7 08:54:29 CST 2024