POSIX::1003::FdIO - POSIX handling file descriptors
use POSIX::1003::FdIO; $fd = openfd($fn, O_RDWR); defined $fd or die $!; # $fd==0 is valid value! (STDIN) $fd = openfd($fn, O_WRONLY|O_TRUNC); $fd = openfd($fn, O_CREAT|O_WRONLY, 0640); # Permission bit constants in POSIX::1003::FS my $buf; $bytes_read = readfd($fd, $buf, BUFSIZ); $bytes_written = writefd($fd, $buf, 5); $off_t = seekfd($fd, 0, SEEK_SET); # rewind! $fd2 = dupfd($fd); closefd($fd) or die $!; my ($r, $w) = pipefd(); writefd($w, "hello", 5); readfd($r, $buf, 5); closefd($r) && closefd($w) or die $!;
Most people believe that the
sys* commands in Perl-Core are not capable of doing unbuffered IO. For those people, we have this module. Whether
sysread() or readfd() is meassurable faster cannot be answered.
Perl defaults to use file-handles avoiding file descriptors. For that reason, the
fread of POSIX is the
read of Perl; that's confusing. The POSIX-in-Core implementation makes you write
POSIX::read() explicitly. However,
POSIX::read() is the same as
For all people who do not trust the
sys* commands (and there are many), we provide the implementation of POSIX-in-Core with a less confusing name to avoid accidents.
POSIX Perl-Core POSIX.pm POSIX::1003::FdIO FH fseek seek FD lseek sysseek lseek seekfd FH fopen open FD open sysopen openfd # sysopen is clumpsy FD fdopen # IO::Handle->new_from_fd FH fclose close FD close close close closefd FH fread read FD read sysread read readfd FH fwrite print FD write syswrite write writefd FH pipe,open # buffered unless $|=0 FD pipe pipe pipefd FH stat stat FD fstat fstat statfd FN lstat lstat FH ftell tell FD tellfd # tell on fd not in POSIX FH rewind rewind FD rewindfd # idem FD creat creat creatfd FD dup dupfd
Works on: FH=file handle, FD=file descriptor, FN=file name
Always check the return code:
undef on error, cause in
$!. closefd $fd or die $!;
There is no
sysclose() in core, because
sysopen() does unbuffered IO via its perl-style file-handle: when you open with
CORE::sysopen(), you must close with
Implemented via openfd(), which is true by definition of POSIX.
Copy file-descriptor FD to an explicit NEWFD number. When already in use, the file at NEWFD will be closed first. Returns undef on failure.
Copy the file-descriptor FD into the lowest-numbered unused descriptor. The new fd is returned, undef on failure.
Returned is an integer file descriptor (FD). Returns
undef on failure (and '0' is a valid FD!)
FLAGS are composed from the
O_* constants defined by this module (import tag
:mode) The MODE field combines
S_I* constants defined by POSIX::1003::FS (import tag
Returns the reader and writer file descriptors. my ($r, $w) = pipefd; writefd($w, "hello", 5 ); readfd($r, $buf, 5 );
Read the maximum of LENGTH bytes from FD into the SCALAR. Returned is the actual number of bytes read. The value
-1 tells you there is an error, reported in
Be warned that a returned value smaller than LENGTH does not mean that the FD has nothing more to offer: the end is reached only when 0 (zero) is returned. Therefore, this reading is quite inconvenient. You may want to use POSIX::Util subroutine readfd_all
The WHENCE is a
Request file administration information about an open file. It returns the same list of values as
stat on filenames.
Attempt to write the first LENGTH bytes of STRING to FD. Returned is the number of bytes actually written. You have an error only when
-1 is returned.
The number of bytes written can be less than LENGTH without an error condition: you have to call write again with the remaining bytes. This is quite inconvenient. You may want to use POSIX::Util subroutine readfd_all
Zillions of Perl programs reimplement these functions. Let's simplify code.
Seek to the beginning of the file
Reports the location in the file. This call does not exist (not in POSIX, nor on other UNIXes), however is a logical counterpart of the
tell() on filenames.
The following constants are exported, shown here with the values discovered during installation of this module.
BUFSIZ 8192 EOF -1 MAX_INPUT 255 O_APPEND 1024 O_ASYNC 8192 O_CLOEXEC 524288 O_CREAT 64 O_DIRECT 16384 O_DIRECTORY 65536 O_DSYNC 4096 O_EXCL 128 O_FSYNC 1052672 O_LARGEFILE 0 O_NDELAY 2048 O_NOATIME 262144 O_NOCTTY 256 O_NOFOLLOW 131072 O_NONBLOCK 2048 O_RDONLY 0 O_RDWR 2 O_RSYNC 1052672 O_SYNC 1052672 O_TRUNC 512 O_WRONLY 1 PIPE_BUF 4096 SEEK_CUR 1 SEEK_DATA 3 SEEK_END 2 SEEK_HOLE 4 SEEK_SET 0 SSIZE_MAX 9223372036854775807 STDERR_FILENO 2 STDIN_FILENO 0 STDOUT_FILENO 1
You can limit the import to the
SEEK_* constants by explicitly using the
:seek import tag. Use the
:mode for all
O_* constants, to be used with openfd().
This module is part of POSIX-1003 distribution version 0.93, built on April 23, 2013. Website: http://perl.overmeer.net. The code is based on POSIX, which is released with Perl itself. See also POSIX::Util for additional functionality.
Copyrights 2011-2013 on the perl code and the related documentation by [Mark Overmeer]. For other contributors see ChangeLog.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See http://www.perl.com/perl/misc/Artistic.html