sleep usage:

while ( not defined $result ) {
    ( $result = try( $something ) ) or sleep 3;
}
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And a select example:

while ( not defined $result ) {
    ( $result = try( $something ) )
        or select undef, undef, undef, 3000;
}
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select can be used to pause for n number of milliseconds, so 3000 would be three seconds. Though this isn't the primary purpose for select, it's a useful side effect. What's useful about it is that you have more resolution than with sleep (which only has one-second granularity).

Probably a more Perlish solution than abusing select would be to use Time::HiRes (which I believe comes with Perl). Its use is as simple as sleep:

use Time::HiRes qw/ usleep /;

while( not defined $result ) {
    ( $result = try( $something ) ) or usleep( 3000 );
}
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