You'll get a warning if you try to tell() on that filehandle but that warning can be suppressed, for we know what we're doing. An unopened handle will return -1 as position:

sub opened($) { my $fh = shift;
    no warnings; #turn 'em off locally
    return tell($fh)==-1 ? undef : 1
}
[download]

HTH

And since we're using the pragma, we can also be more specific about which warnings we don't want. Then we can lose the prototype for errorchecking too (which it only does shoddily anyway). And lastly, undef is a one-element list and evaluates as true in list context, so we just let Perl decide what value the boolean expression should return.

sub is_opened {
    no warnings qw(closed unopened);
    return tell $_[0] != -1;
}
[download]

Update: Oops. s/==/!=/ - otherwise the truth value is reversed of course. Thanks, blakem.

Update 2: and of course, check perldoc perllexwarn about the detailed warning names you can use to enable/disable specifically.

Update 3 (the neverending story): fruiture informs me that you have to disable not only the closed category, but unopened as well. Code updated accordingly.

Makeshifts last the longest.

no warnings;

Kinky. I never saw that piece of code before. I like it though. Thank you.

-- Bow before Zod!

The fcntl function allows you to read the filehandle's modes. If *FOO is open and you want to see if it is writeable:

# named constants for portability
use Fcntl qw( F_GETFL O_WRONLY O_RDONLY O_RDWR);
if ( (O_WRONLY | O_RDWR) & fcntl( FOO, F_GETFL, 0) ) {
     # g'wan and write
}
[download]

If the handle is not open fcntl returns undef.

Update: Aristotle, yes, but it would be good to check $! the see just what the error was. EBADF says the handle isn't open.

After Compline,
Zaxo

Wouldn't it then suffice to check like so?

sub is_opened {
    return defined fcntl $_[0], F_GETFL, 0;
}
[download]

Makeshifts last the longest.