An alternative to JavaFan's use of a capture in the split regexp could be to use look-arounds to do the split at points where the string changes from non-digit to digit and vice-versa. I think JavaFan's method is better in this case but the look-arounds can sometimes be a useful technique.

$ perl -le '
> $_ = q{BS123-bleble};
> print +( split m{(?x) (?: (?<=\D)(?=\d) | (?<=\d)(?=\D) )} )[ 1 ];'
123
$
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I hope this is of interest.

Cheers,

JohnGG