Question

For example, given the string ‘2009/11/12’ I want to get the regex (‘\d{2}/d{2}/d{4}’), so I’ll be able to match ‘2001/01/02’ too.

Is there something that does that? Something similar? Any idea’ as to how to do it?

Answer 1

There is text2re, a free web-based ‘regex by example’ generator.

I don’t think this is available in source code, though. I dare to say there is no automatic regex generator that gets it right without user intervention, since this would require the machine knowing what you want.

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Note that text2re uses a template-based, modularized and very generalized approach to regular expression generation. The expressions it generates work, but they are much more complex than the equivalent hand-crafted expression. It is not a good tool to learn regular expressions because it does a pretty lousy job at setting examples.

For instance, the string '2009/11/12' would be recognized as a yyyymmdd pattern, which is helpful. The tool transforms it into this 125 character monster:

((?:(?:[1]{1}\d{1}\d{1}\d{1})|(?:[2]{1}\d{3}))[-:\/.](?:[0]?[1-9]|[1][012])[-:\/.](?:(?:[0-2]?\d{1})|(?:[3][01]{1})))(?![\d]) 

The hand-made equivalent would take up merely two fifths of that (50 characters):

([12]\d{3})[-:/.](0?\d|1[0-2])[-:/.]([0-2]?\d|3[01])\b