IO::Handle(3) Perl Programmers Reference Guide IO::Handle(3)NAMEIO::Handle - supply object methods for I/O handles
SYNOPSIS
use IO::Handle;
$fh = new IO::Handle;
if ($fh->fdopen(fileno(STDIN),"r")) {
print $fh->getline;
$fh->close;
}
$fh = new IO::Handle;
if ($fh->fdopen(fileno(STDOUT),"w")) {
$fh->print("Some text\n");
}
use IO::Handle '_IOLBF';
$fh->setvbuf($buffer_var, _IOLBF, 1024);
undef $fh; # automatically closes the file if it's open
autoflush STDOUT 1;
DESCRIPTIONIO::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
A IO::Handle object is a reference to a symbol (see the
Symbol package)
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:
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close
fileno
getc
eof
read
truncate
stat
print
printf
sysread
syswrite
See the perlvar manpage for complete descriptions of each
of the following supported IO::Handle methods:
autoflush
output_field_separator
output_record_separator
input_record_separator
input_line_number
format_page_number
format_lines_per_page
format_lines_left
format_name
format_top_name
format_line_break_characters
format_formfeed
format_write
Furthermore, for doing normal I/O you might need these:
$fh->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.
$fh->opened
Returns true if the object is currently a valid file
descriptor.
$fh->getline
This works like <$fh> described in the section on I/O
Operators in the perlop manpage except that it's more
readable and can be safely called in an array context
but still returns just one line.
$fh->getlines
This works like <$fh> when called in an array 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.
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$fh->ungetc ( ORD )
Pushes a character with the given ordinal value back
onto the given handle's input stream.
$fh->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.
$fh->flush
Flush the given handle's buffer.
$fh->error
Returns a true value if the given handle has
experienced any errors since it was opened or since
the last call to clearerr.
$fh->clearerr
Clear the given handle's error indicator.
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. 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! Note that you need to import the constants
_IOFBF, _IOLBF, and _IONBF explicitly.
Lastly, there is a special method for working under -T and
setuid/gid scripts:
$fh->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.
NOTE
A IO::Handle object is a GLOB reference. 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'.
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IO::Handle(3) Perl Programmers Reference Guide IO::Handle(3)SEE ALSO
the perlfunc manpage, the section on I/O Operators in the
perlop 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
<bodg@tiuk.ti.com>
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