Unfortunately perl does not have any built-in functions to do just this. One way you could check it is by seeing if perl warns "... is not numeric ..." when you try to do something with a value:

# numeric -- returns true if arg. is numeric
sub numeric {
  my $value = shift;
  my $result = 1;
  local $^W = 1; # turn warnings on if they aren't already.
  local $SIG{__WARN__} = sub { $result = 0 };
     # if we get a warning make $result false
  $value += 0;
  return $result;
}
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