IO::Handle(3p) Perl Programmers Reference Guide IO::Handle(3p) #
IO::Handle(3p) Perl Programmers Reference Guide IO::Handle(3p)
NNAAMMEE #
IO::Handle - supply object methods for I/O handles
SSYYNNOOPPSSIISS #
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;
DDEESSCCRRIIPPTTIIOONN #
"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.
CCOONNSSTTRRUUCCTTOORR #
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.
MMEETTHHOODDSS #
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 ccrrooaakk(()) 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 ffssyynncc(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 sseettbbuuff(()) and/or sseettvvbbuuff(()) 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 sseettvvbbuuff(())--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 IIOO::::HHaannddllee::::sseettvvbbuuff(()) is not available by default on Perls
5.8.0 and later because sseettvvbbuuff(()) 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" mmuusstt nnoott bbee
mmooddiiffiieedd 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 --TT 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)
NNOOTTEE #
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'.
SSEEEE AALLSSOO #
perlfunc, "I/O Operators" in perlop, IO::File
BBUUGGSS #
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.
HHIISSTTOORRYY #
Derived from FileHandle.pm by Graham Barr <_g_b_a_r_r_@_p_o_b_o_x_._c_o_m>
perl v5.36.3 2023-02-15 IO::Handle(3p)