Ruby simple regex syntax error

Question

I'm new to Ruby and i'm working on a code for a server. The code is a half year old. In the meanwhile Chrome updated versions to version 14.

So here is my code:

supported_browsers = /Chrome\/[3-9]|Firefox\/[3-9]|\sMSIE\s|Konqueror\/[4-9]|Midori|Minefield|Shiretoko|IceCat|Opera\/9.|\sAppleWebKit/

As you can see Chrome 3-9 but now when i try to change it to:

supported_browsers = /Chrome\/[3-15]|Firefox\/[3-9]|\sMSIE\s|Konqueror\/[4-9]|Midori|Minefield|Shiretoko|IceCat|Opera\/9.|\sAppleWebKit/

I get a syntax error. Help me figure out what's wrong.

Toto · Accepted Answer · 2011-10-02 10:01:52Z

3

Your error is here : [3-15] this is a character class with range of char from 3 to 1 that is not allowed.

I guees you want : [3-9]|1[0-5] that means 3 to 9 or 10 to 15

The complete regex is:

supported_browsers = /Chrome\/([3-9]|1[0-5])|Firefox\/[3-9]|\sMSIE\s|Konqueror\/[4-9]|Midori|Minefield|Shiretoko|IceCat|Opera\/9.|\sAppleWebKit/

answered Oct 2, 2011 at 10:01

Toto

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Comments

Simone Carletti · Accepted Answer · 2011-10-02 10:12:42Z

3

[3-9] is a numeric range. It means a single digit between 3 or 9. Numeric ranges doesn't work in the way you expect: [3-15] is not a valid range.

If you simply want to match a digit range you can use [0-9]{1,2}. It matches everything between 0 and 99. Or [0-9]+ to make it less restrictive.

supported_browsers = /Chrome\/[0-9]+|Firefox\/[3-9]|\sMSIE\s|Konqueror\/[4-9]|Midori|Minefield|Shiretoko|IceCat|Opera\/9.|\sAppleWebKit/

If you really want to validate the inclusion in the range 3-15, using regular expressions is not really the best choice. In fact, using regular expression your range should be [3-9]|1[0-5] and the more restrictive you want to be, the more complicated the regexp becomes.

supported_browsers = /Chrome\/(?:[3-9]|1[0-5])|Firefox\/[3-9]|\sMSIE\s|Konqueror\/[4-   9]|Midori|Minefield|Shiretoko|IceCat|Opera\/9.|\sAppleWebKit/

edited Oct 2, 2011 at 10:12

answered Oct 2, 2011 at 10:02

Simone Carletti

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3 Comments

Tom Over a year ago

Why isn't it the best choice?

Simone Carletti Over a year ago

I told you in the last sentence: the more sophisticated the match becomes, the more complex is your regexp. There is a point where you need to leave regexp and use code. For example, what would happen if you don't support Chrome 13? Validating a range 3-15 except 13 using a regexp forces you to write extremely complicated regexps.

Simone Carletti Over a year ago

Anyway, for now you can still use regexps but remember, when exceptions will arrive, don't try to solve everything in a regexp or simplify the problem. Do you really need to check the version number? Keep in mind that Chrome has a built-in update system, it's very unlikely that a user has a Chrome version < 3.

Jayendra · Accepted Answer · 2011-10-02 10:16:13Z

1

[3-15] does not check the range. for range you have to use [3-9]|1[0-4] would match 1-14 e.g.

supported_browsers = /Chrome\/([3-9]|1[0-4])|Firefox\/[3-9]|\sMSIE\s|Konqueror\/[4-9]|Midori|Minefield|Shiretoko|IceCat|Opera\/9.|\sAppleWebKit/

edited Oct 2, 2011 at 10:16

answered Oct 2, 2011 at 10:04

Jayendra

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1 Comment

Simone Carletti Over a year ago

[1-9][0-4] also matches 94.

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