The pattern Aar will look for all texts that contain a capital A followed by a small a and r. If the case sensitive box is not ticked, the capitalization will not matter.

The pattern 123 finds all texts that contain this number. Note that texts with the number 41235 are also matched, since 123 is a textual part of that.

As you can see, this does not differ from regular text matching yet. With regular expressions, we can also say that we expect any letter or any number. We can give a set of characters from which can be chosen by surrounding the alternatives with square brackets []. We can indicate a character range in those brackets by separating the limits with a hyphen.

The pattern [0123456789] matches all texts that contain a number.

The pattern [0-9] does the same, only it is more condense. It says everything between 0 and 9 is fine.

Similarly, the pattern [a-z] matches all lowercase letters (and also uppercase if the case-sensitive option is not used). [A-Z] matches uppercase letters and [a-zA-Z] matches all letters, regardless of the case-sensitive option.

If you want to look for numbers and letters, use [0-9a-zA-Z]. Read this as "every character between 0 and 9, between a and z, or between A and Z".

As in the earlier examples, we can put several matchers next to each other. analy[sz]e will match both American (analyze) and British (analyse) spellings.

Similarly, the expression [0-9][a-z] will find numbers directly followed by at least one letter. The expression [a-z][0-9][0-9][0-9] finds letters directly followed by at least three numbers.

If you want to find measurements such as 1 cm or 25 in, you will not find them with the preceding expressions because of the space in between. Luckily, a space is also a symbol, so the expression [0-9] [a-z] will find them. Note the space in between the bracket pairs, and note the fact that this will even find longer measurements such as 12345 meters. Indeed, the expression matches a number followed by a space and a letter, so in this case, 5 m. It doesn't matter whether other numbers or letters are also present.

If you're just looking for measurements in inches, the expression [0-9] in will do the job.

It might be a bit cumbersome to write [0-9] in full every time. This is why shorthand character classes were introduced. They are symbols that stand for a set of characters. For instance, the symbol \d stands for any digit and is thus equivalent to [0-9], but a lot faster to write. The opposite is \D, which means anything that is not a digit and includes letters as well as symbols. Unfortunately, there is no shorthand for any letter, but there is a shorthand for any letter, number, or underscore, which is \w, which stands for any word character. Again, the opposite is \W, which matches for all non-letters and non-numbers that are not underscores either.

\d [a-z] will again match for texts with measurements: any number followed by a space and a letter.

\d\d\d matches texts with numbers with a length of at least three.

\D\D matches texts that have at least two consecutive non-numbers. If you're surprised to see texts with numbers as well, think about it: the expression only says that the text should contain a non-number followed by a non-number; it doesn't say that there should be no numbers at all. However, if a text field only contains numbers, it won't be matched. To rephrase, the expression means "I'm looking for two non-numbers in a row, do you have them?"

You might wonder how \D works. Does it then translate to a huge set that includes everything but numbers? The answer is more simple: using a caret ^ as the first character in braces means none of the characters should be present in the pattern. Therefore, \D stands for [^0-9].

The expression [^a-zA-Z0-9] looks for texts that contain something which is not a letter or number. Most texts will match, as for instance spaces and punctuation marks are still allowed. However, empty fields will not match, as there must be at least one character which is not a letter or number.

The expression [^a-zA-Z0-9]\d[^a-zA-Z0-9] means any digit surrounded by non-letters or non-numbers. For instance, we see that single digits in parentheses are matched. Note that items such as (123) will not be matched, but (3) will, as we explicitly say that it should be a single digit.

The pattern a.a.a matches any text where an a is followed by any character, another a, any character, and another a. For instance, texts with the words dulcamara, alabaster, and salamander will match.

The pattern 19.. (there is a space before and after) will match years in the 20th century.

However, you should be careful with the dot: the last pattern also matches 19th and 19M$, because a dot really means anything. If a year is what you want, 19\d\d is more accurate.

To find texts that have three consecutive dots in them, use \.\.\.. (This can actually be done in a more handy way, as we'll see in the next section.)

To find texts with a backslash, use \\. (There are none in the dataset.)

Texts that contain an opening or a closing square bracket are found with [\[\]]. This looks complicated, but it is quite logical: the first and last bracket say "choose any of the things within". And the things within are actual square brackets, but they have to be escaped, so they become \[ and \].

With [2], you find texts that contain the number 2 ("choose any of the things within", and the only thing within is a 2). With \[2\], you find texts with the number 2 surrounded in square brackets, as the brackets are escaped this time and thus have no special meaning anymore.

bre+d matches texts that contain bred, breed, or breeed with any number of e, as long as at least one e is present.

bre*d matches texts that contain brd, bred, breed, or breeed with any number of e, even without. Note how brd is matched with the asterisk, but not with the plus sign.

bre?d matches brd and bred, but not breed or any other number of es. Put simply, it makes the e optional.

Combinations are also possible. br?e+d matches bed, bred, beed, breed, beeed, breeed, and so on.

In addition, you can be explicit about the number of times you would like a symbol to occur by using curly braces {min,max}. You can specify the minimum and maximum number of times it can occur. Either one can be empty, in which case there is no minimum or maximum. Leave the comma in so OpenRefine knows whether you specified the minimum or the maximum. If you just supply a single number without a comma, the exact number of times will be matched.

N\d{5,8}, matches texts that contain a code that starts with N followed by five, six, seven, or eight digits, and then a comma.

N\d{5,}, matches texts that contain a code that starts with N, at least five digits, and then a comma.

N\d{,8}, matches texts which contain a code that starts with N, at most eight digits, and then a comma.

N\d{5}, matches texts which contain a code that starts with N, exactly five digits, and then a comma. This is equivalent to N\d\d\d\d\d but much more compact (especially if numbers get large).

Needless to say, the quantifiers and braces are special symbols, so if you want to match them literally, you should escape them with a backslash. For instance, question marks can be matched with \?.

^\d matches all texts that begin with a number.

\d$ matches all texts that end with a number.

^\d.*\d$ matches all texts that begin and end with a number. Read this expression as: start of the text, a number, zero or more times any character (the dot), a number, end of the text. If we would use ^\d+$ instead, we would have all texts that contain only a number (of any length).

\b\d{3}\b searches for texts that contain at least one number of exactly three digits, since the \b anchor matches at word boundaries. If the text contains four-digit numbers but no three-digit numbers, it does not match. (If we would remove the \b anchors, it would.)

^\d{3}\b finds texts that start with a three-digit number.

glass|wood|steel will match texts that contain glass, wood, or steel.

\d+|many|few matches either a number, many or few.

N\d{5},|N\d{8}, matches either five-digit or eight-digit numbers that start with an N and end with a comma, but nothing in between (so no six-digit numbers for instance).

While la+ matches texts that contain la, laa, laaa, and so on, the expression (la)+ finds texts that contain la, lala, lalala, and so on.

The expression analyz|se would match texts that contain analyz and texts that contain se. This is probably not that useful. On the other hand, the expression analy(z|s)e matches both analyze and analyse. Note that in this case, this is equivalent to analy[zs]e because the choice consists of a single letter. However, this would not be the case with analyz(e|ing), which would match analyze and analyzing.