# Regular Expressions **URL:** \ **Category:** Ruby\ **Created:** [June 17, 2008, 6:09pm UTC](https://www.ruby-forum.com/t/regular-expressions/140702 "2008-06-17T18:09:25Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![jturney](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e99b99/32.png) [@jturney](https://www.ruby-forum.com/u/jturney)\ **Post date:** [June 17, 2008, 6:09pm UTC](https://www.ruby-forum.com/t/regular-expressions/140702/1 "2008-06-17T18:09:25Z")
Hello! I’m trying this problem that says I must match versions in a CSV file, could be anything like: v.6.0.3-3 aajd4-43\_3 ABCD 5.0 ABCDv.5.0 A 3.40 … With the other fields in mind, I thought “heck, looks like versions are the only ones that contain a series of letters, digits, periods, underscores and dashes…” I’m pretty new to Ruby so I don’t have very much experience with regular expressions. Is it possible to make just one regular expression to fulfill my problem? I need a regular expression that will return: v.6.0.3-3: true because there’s a v followed by a series of ‘.’ and digits aajd4-43\_3: true because there’s a series of digits, ‘-’, and ‘\_’ ABCD 5.0: true because there’s a series of digits and ‘.’ ABCDv.5.0: true… A 3.40: true… Thanks for the help! ---
**Author:** ![jturney](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e99b99/32.png) [@jturney](https://www.ruby-forum.com/u/jturney)\ **Post date:** [June 17, 2008, 6:49pm UTC](https://www.ruby-forum.com/t/regular-expressions/140702/2 "2008-06-17T18:49:09Z")
On Tue, Jun 17, 2008 at 6:08 PM, Justin To [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > … > digits > aajd4-43\_3: true because there’s a series of digits, ‘-’, and ‘\_’ > ABCD 5.0: true because there’s a series of digits and ‘.’ > ABCDv.5.0: true… > A 3.40: true… I think there’s some information missing here: how many of these characters form a “series”? More than 1? Do they have to be interleaved in some order, like, you need digits followed by a . a - or a \_ followed by more digits, or it doesn’t matter. The simplest case: two or more of those characters in a row: irb(main):023:0\> versions = [“v.6.0.3-3”, “aajd4-43\_3”,“ABCD 5.0”, “ABCDv.5.0”, “A 3.40”] =\> [“v.6.0.3-3”, “aajd4-43\_3”, “ABCD 5.0”, “ABCDv.5.0”, “A 3.40”] irb(main):024:0\> r = /[.-\_1-9]{2,}/ =\> /[.-\_1-9]{2,}/ irb(main):025:0\> versions.each {|x| puts “#{x}: #{(x =~ r) != nil}”} v.6.0.3-3: true aajd4-43\_3: true ABCD 5.0: true ABCDv.5.0: true A 3.40: true 1 or more digits, followed by . or \_ or -, followed by one or more digits: irb(main):030:0\> r = /\d+[-._]\d+/ =\> /\d+[-._]\d+/ irb(main):031:0\> versions.each {|x| puts “#{x}: #{(x =~ r) != nil}”} v.6.0.3-3: true aajd4-43\_3: true ABCD 5.0: true ABCDv.5.0: true A 3.40: true You will have to refine your requirements a little bit, in order to choose among these (and any variations on this). Jesus. ---
**Author:** ![jturney](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e99b99/32.png) [@jturney](https://www.ruby-forum.com/u/jturney)\ **Post date:** [June 17, 2008, 6:50pm UTC](https://www.ruby-forum.com/t/regular-expressions/140702/3 "2008-06-17T18:50:54Z")
On 17.06.2008 18:08, Justin To wrote: > … > digits > aajd4-43\_3: true because there’s a series of digits, ‘-’, and ‘\_’ > ABCD 5.0: true because there’s a series of digits and ‘.’ > ABCDv.5.0: true… > A 3.40: true… > > Thanks for the help! Yes, that’s easy, just /./ as an expression. Seriously, it is similarly crucial what it does _not_ match. The easiest (but not most efficient approach) would be to create on alternative for each variant you have, like %r{ ^(?: v(?:.\d+)±\d+ | \w+\d±[\d\_]+ | … )$ }x etc. But given the number of alternatives you present it might be difficult to avoid also matching other stuff. At least, you’ll face a pretty complex regular expression. Kind regards robert ---
**Author:** ![jturney](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e99b99/32.png) [@jturney](https://www.ruby-forum.com/u/jturney)\ **Post date:** [June 18, 2008, 1:42pm UTC](https://www.ruby-forum.com/t/regular-expressions/140702/4 "2008-06-18T13:42:22Z")
Robert K. wrote: > The easiest (but not most efficient approach) would be to create on > alternative for each variant you have, like > > %r{ > ^(?: > v(?:.\d+)±\d+ > | \w+\d±[\d\_]+ > | … > )$ > }x > > etc. The problem with regular expressions is that they can easily get out of hand and become incomprehensible, as the above code shows (though presumably to RK it’s totally transparent). Better to write a number of small regexps, each testing for a specific pattern. Then combine the results with a logical OR. This can be done using a flag variable, or an if-elsif tree, a case statement, etc., whatever you feel happiest with. This approach will be a lot easier to test and debug. ---
**Author:** ![jturney](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e99b99/32.png) [@jturney](https://www.ruby-forum.com/u/jturney)\ **Post date:** [June 18, 2008, 2:23pm UTC](https://www.ruby-forum.com/t/regular-expressions/140702/5 "2008-06-18T14:23:06Z")
2008/6/18 Dave B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > > }x > > > > etc. > > The problem with regular expressions is that they can easily get out of > hand and become incomprehensible, as the above code shows (though > presumably to RK it’s totally transparent). Actually the RX I presented was not complete and was intended to convey your point. 🙂 > Better to write a number of small regexps, each testing for a specific > pattern. Then combine the results with a logical OR. This can be done > using a flag variable, or an if-elsif tree, a case statement, etc., > whatever you feel happiest with. This approach will be a lot easier to > test and debug. Depends. If you build the one RX one alternative at a time and test during each iteration I’d say that works pretty good as well. And if the volume of data is hight the performance advantage of a single RX might pay off. Kind regards robert