select(REPORT1);
    $^ = 'report1_top';
    select(REPORT2);
    $^ = 'report2_top';

FILEHANDLE may be an expression whose value gives the name of the actual filehandle. Thus:

    $oldfh = select(STDERR); $| = 1; select($oldfh);

Some programmers may prefer to think of filehandles as objects with methods, preferring to write the last example as:

    use IO::Handle;
    STDERR->autoflush(1);

    $rin = $win = $ein = '';
    vec($rin,fileno(STDIN),1) = 1;
    vec($win,fileno(STDOUT),1) = 1;
    $ein = $rin | $win;

If you want to select on many filehandles you might wish to write a subroutine:

    sub fhbits {
        local(@fhlist) = split(' ',$_[0]);
        local($bits);
        for (@fhlist) {
            vec($bits,fileno($_),1) = 1;
        }
        $bits;
    }
    $rin = fhbits('STDIN TTY SOCK');

The usual idiom is:

    ($nfound,$timeleft) =
      select($rout=$rin, $wout=$win, $eout=$ein, $timeout);

or to block until something becomes ready just do this

    $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef);

Most systems do not bother to return anything useful in $timeleft, so calling select() in a scalar context just returns $nfound.

Any of the bit masks can also be undef. The timeout, if specified, is in seconds, which may be fractional. Note: not all implementations are capable of returning the $timeleft. If not, they always return $timeleft equal to the supplied $timeout.

You can effect a sleep of 250 milliseconds this way:

    select(undef, undef, undef, 0.25);

WARNING: Do not attempt to mix buffered I/O (like read() or < FH>) with select(). You have to use sysread() instead.