如何确定Perl文件句柄是读取还是写入句柄？

You are given either an IO::File object or a typeglob (\*STDOUT or Symbol::symbol_to_ref("main::FH")); how would you go about determining if it is a read or write handle? The interface cannot be extended to pass this information (I am overriding close to add calls to flush and sync before the actual close).

您将获得IO :: File对象或typeglob（\ * STDOUT或Symbol :: symbol_to_ref（“main :: FH”））;您将如何确定它是读取还是写入句柄？该接口无法扩展以传递此信息（我在实际关闭之前覆盖接近添加刷新和同步的调用）。

Currently I am attempting to flush and sync the filehandle and ignoring the error "Invalid argument" (which is what I get when I attempt to flush or sync a read filehandle):

目前我正在尝试刷新和同步文件句柄并忽略错误“无效参数”（这是我尝试刷新或同步读取文件句柄时得到的）：

eval { $fh->flush; 1 } or do {
        #this seems to exclude flushes on read handles
        unless ($! =~ /Invalid argument/) {
                croak "could not flush $fh: $!";
        }
};

eval { $fh->sync; 1 } or do {
        #this seems to exclude syncs on read handles
        unless ($! =~ /Invalid argument/) {
                croak "could not sync $fh: $!";
        }
};

1 个解决方案

#1

Have a look at the fcntl options. Maybe F_GETFL with O_ACCMODE.

看看fcntl选项。也许F_GETFL与O_ACCMODE。

Edit: I did a little googling and playing over lunch and here is some probably non-portable code but it works for my Linux box, and probably any Posix system (perhaps even Cygwin, who knows?).

编辑：我做了一些谷歌搜索和午餐玩，这里有一些非可移植的代码，但它适用于我的Linux盒子，可能是任何Posix系统（甚至可能是Cygwin，谁知道？）。

use strict;
use Fcntl;
use IO::File;

my $file;
my %modes = ( 0 => 'Read only', 1 => 'Write only', 2 => 'Read / Write' );

sub open_type {
    my $fh = shift;
    my $mode = fcntl($fh, F_GETFL, 0);
    print "File is: " . $modes{$mode & 3} . "\n";
}

print "out\n";
$file = new IO::File();
$file->open('> /tmp/out');
open_type($file);

print "\n";

print "in\n";
$file = new IO::File();
$file->open('< /etc/passwd');
open_type($file);

print "\n";

print "both\n";
$file = new IO::File();
$file->open('+< /tmp/out');
open_type($file);

Example output:

输出示例：

$ perl test.pl 
out
File is: Write only

in
File is: Read only

both
File is: Read / Write

#1