learning about regular expressions

Source: regexcrossword.com

Tutorial

This tutorial introduces us to some Regex patterns using a crossword-style approach.

• A | Z, A | B. This means, the answer must satisfy two conditions. It must contain an A or a Z, and it must contain an A or a B. A matches both conditions.
• [ABC], [BDF]. This means, the answer must contain an A, a B, or a C, and it must contain a B, a D or an F. B is the only thing found in both ranges.
• [ABC], [^AB]. This means, the answer must contain an A or a B or a C, but it must NOT (^) contain an A or a B. The only answer that meets both these conditions is the letter C.
• We have a two character answer. The first character must contain an A (A), and it must also contain 0 or more As (A*). The second character must contain 0 or more As or Bs. So the answer will be 'AA'.
• We have a two character answer. The first character must contain an A or a C (A | C), and it must also contain zero or one As and zero or one Bs (A?B?). The second character must contain a B. So the answer is 'AB'.
• We have a two character answer. The first character must have an A or a B (A|B), and it must have one or more As (A+). The second character must be an A or a Z, and also have one or more A characters (A|Z, A+). The answer is 'AA'.
• We have a two character answer. Both the first and second character must contain an A or a B (A|B), and the second character must contain the results of th first capture group, which in this case happens to be an A. So the answer is AA.
• We have a two character answer. The first caracter must contain 1 A. The second character must contain a B or an A. Both characters must contain 2 or mor As ({2,})
• We have a one character answer. It must contain a space, and it must contain an A or a space.

Beginner problems

It's going to be too difficult to write out the whole logic process for solving the crossword-type problems in these examples. So instead I'll just record each of the rules and what they mean.

• [^SPEAK]+ means must not contain one or more of the characters S,P,E,A or K.
• [PLEASE]+ means must contain one or more of the characters P,L,E,A,S,E.
• HE | LL | O+ means must contain 'HE' or 'LL' or one or more 'O's.
• EP | IP | EF means must contain 'EP' or an 'IP' or an 'EF'.
• (A|B|C)\1 means must be either an A or a B or a C
• (AB | OE | SK) means must be 'AB', or an 'OE' or an 'SK'.
• .*M?O.* means 0 or more of any character (.*), then 0 or one M (M?), then O, then 0 or more of any characters (.*).
• (AN | FE | BE) means must be an 'AN' or an 'FE' or a 'BE'.
• [COBRA]+ must contain one of any of these characters: C,O,B,R, or A.
• (AB | O | OR)+ means must contain one or more of the character groups 'AB', 'O' or 'OR'.
• (.)+\1 means the first character must be 0 or more of the following character, which must be the result of the first chracter.
• [^ABRC]+ means, must not be one or more of one of the characters A,B,R or C.
• [*]+ means must contain one or more of any character
• [*]+ means one or more of the * character
• .?.+ means character one must be 0 or more of any character. Character 2 must be 1 or more of any character.