The Alphabet Used in Regular Expressions

Item name Conventional regular expression sign Usage examples and explanations
Any character . c.t - denotes words like «cat», «cot»
Character from a character range  [] [b-d]ell - denotes words like «bell», «cell», «dell»

[ty]ell - denotes words "tell" and "yell".
Character out of a character range [^] [^y]ell - denotes words like "dell", "cell", "tell", but forbids "yell"

[^n-s]ell - denotes words like "bell", "cell", but forbids "nell", "oell", "pell", "qell", "rell" and "sell"
Or | c(a|u)t - denotes words "cat" and "cut"
0 or more occurrences in a row * 10* - denotes numbers 1, 10, 100, 1000 etc.
1 or more occurrences in a row + 10+ - it allows numbers 10, 100, 1000 etc., but forbids 1.
Letter or digit [0-9a-zA-Zа-яА-Я] [0-9a-zA-Zа-яА-Я] - it allows a single character; 
[0-9a-zA-Zа-яА-Я]+ - it allows any word
Capital Latin letter  [A-Z]  
Small Latin letter  [a-z]  
Capital Cyrillic letter [А-Я]  
Small Cyrillic letter [а-я]  
Digit [0-9]  
Space \s  
Character, used by system. @  

Note:

  1. Some characters used in regular expressions are "auxiliary", i.e. they are used for system purposed. As you can see from the list above, such characters are square brackets, periods, etc. If you'd like to enter an auxiliary character as a normal one, put a backslash (\) before it. Example: [t-v]x+ denotes words like tx, txx, txx, etc., ux, uxx, etc., but \[t-v\]x+ denotes words like [t-v]x, [t-v]xx, [t-v]xxx etc.
  2. If you need to group certain regular expression elements, use brackets. For example, (a|b)+|c denotes c and any combinations like abbbaaabbb, ababab, etc. (a word of any non-zero length in which there may be any number of a's and b's in any order), whilst a|b+|c denotes a, c, and b, bb, bbb, etc.

Sample regular expressions

Suppose you need to recognize "personal data" tables (we'll use sample Russian personal data document), and suppose these tables contain such fields as passport issue date, the First and Last Names, and the passport series and number. You may create new Data and Passport languages and set regular expressions for them.  

"Issue Date" language

The number denoting day may consist of one digit (e.g. 1, 2 etc.) or two digits (e.g. 02, 12), but it cannot be zero (00 or 0). The regular expression for the day should then look like this: ((|0)[1-9])|([1|2][0-9])|(30)|(31).

The regular expression for the month should look like this: ((|0)[1-9])|(10)|(11)|(12).

The regular expression for the year should look like this: ([19][0-9][0-9]|([0-9][0-9])|([20][0-9][0-9]|([0-9][0-9]).

What is left is to combine all this together and separate the numbers by period (like 1.03.1999). The period is an auxiliary sign, so we must put a backslash (\) before it. The regular expression for the full date should then look like this:

((|0)[1-9])|([1|2][0-9])|(30)|(31)\. ((|0)[1-9])|(10)|(11)|(12)\.((19)[0-9][0-9])|([0-9][0-9])|([20][0-9][0-9]|([0-9][0-9])

"Passport series" language

The Russian passport series is a Roman number from the following set: 1-10, 20, and 30, then a hyphen, then two capital Cyrillic letters, like VI-СБ, or XXX-МЮ. The regular expression for the passport series should look like this:

((|X|XX|XXX)(|I|II|III|IV|V|VI|VII|VIII|IX))-[А-Я][А-Я]

"E-mail address" language

You can easily make a language for denoting e-mail addresses. The regular expression for an e-mail address should look like this:

[a-zA-Z0-9_\-\.]+\@[a-z0-9\.\-]+