I note that each of your test strings has either a single valid number, or a single invalid sequence of digits and dots. What should be the result of, eg, '12.34 and 56.78', or '12.34 on 2004.04.12' or 'on 2004.04.12 found 12.34'?

Your question is also a little unclear in that you ask that the answer be "efficiently" achieved; but "efficient" is a relative term - what counts as "efficient enough"? (Is there a maximum length of strings that must be parsed within whatever limits you set?)

As far as I remember the CUT operator /(?>...)/ is not implemented in a hugely efficient manner, but it may well be sufficient for your needs. You might use that something like:

m{
  ^ [^-+\d.]*
  (?> (    (?# cut and capture)
    [-+]? (?: \.\d+ | \d+ (?: \. \d* )? )
  ) )
  (?!\.)
}x

[download]

This (giving the result in $1) appears to pass your existing tests, and finds "12.34" for my first two additional cases and no match for the third.

Update: on second thoughts, the cut should not be necessary, just need to expand the tailing negative lookahead:

m{
  ^ [^-+\d.]*
  (
    [-+]? (?: \.\d+ | \d+ (?: \. \d* )? )
  )
  (?![.\d])
}x

[download]

Note also that the efficiency of CUT is suboptimal mainly when it is being hit repeatedly (eg as part of an alternation in a larger pattern), so it should be fine in this case anyway.

Hugo

In reply to Re: Best practice validating numerics with regex? by hv
in thread Best practice validating numerics with regex? by perlboy_emeritus

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