Character(s)

Meaning

.

Any character may be entered by the user at the position of this character in the regular expression. For example: .... means that the user may enter four random characters.

*

The preceding character or expression may occur zero or more times. For example: [0-9]* indicates that any number from 0 through 9 may occur zero or more times at the position of * in the regular expression.

Note that some special regular expression syntax applies in field and screen conditions, also relating to the use of an asterisk.

+

The preceding character or expression must occur at least once but may also occur more times. For example: [b-f]+ indicates that any letter from b through f may occur one or more times at the position of + in the regular expression.

?

The preceding character may occur 0 or 1 times at the position of ? in the regular expression. For example: !? means that ! may occur here once, or not at all.

[characters]

Insert all the characters that are allowable for input by the user at this position in the regular expression, between the brackets, without spaces in between the characters, for example: [aHgm].

[x-y]

The allowed input of one character falls within the range x - y, for instance [a-z] or [0-9].
More than one range can also be provided, by placing them directly behind each other between the brackets, for example: [0-9a-z].

[^characters]

Insert all the characters or a range between the brackets and after the '^' symbol that may not occur at this position. For example: [^0-9] which means that the numbers 0 through 9 may not occur at this position.

^

Only when this character is inserted at the very beginning of a regular expression, it means that input should start with the expression or characters following this character.

$

This character indicates the end of the allowable input. No more characters may be entered by the user.

\character

The character that may occur at this position is a special character reserved for use in a regular expression. An example is the full stop, which is used in regular expressions as a wildcard. If you want the user to be able to enter a full stop as a character, place it behind a backslash: \.
Another example is \?|\*|\^ which means that the user may either enter a ?, a * or a ^.

expression 1|expression 2

Allowed input either matches expression1 or expression2. The symbol for OR is a vertical line. For example: ^[0-9]$|^x$ means that the user may enter either a number or an x.

Character(s)

Allowed input

h..se

an h followed by any two characters, followed by se. This would match horse and house, for example.

The.*house

the text The followed by any one or more characters, followed by house. This would match: The house, The new house, The boathouse, but not Thehouse.

[Ee]xample

the word example, spelt with either a capital or a lower case e.

l[aeiou]nger

a word with a vowel at the second position. For example: longer, linger, etc.

[1-9][0-9][0-9][0-9] [A-Z][A-Z]

the regular expression for Dutch postcodes. Allowed values are: 1234HK or 9000ZA, but not 0434AB or 3456hj.

^book$|^serial$

the word book or the word serial.

^[a-z]*$|^[0-9]*$

a random length string of lower case letters or a random length string of digits