Reference

Regular Expressions

The pattern and patternProperties keywords use regular expressions to express constraints. The regular expression syntax used is from JavaScript (ECMA 262, specifically). However, that complete syntax is not widely supported, therefore it is recommended that you stick to the subset of that syntax described below.

  • A single unicode character (other than the special characters below) matches itself.
  • .: Matches any character except line break characters. (Be aware that what constitutes a line break character is somewhat dependent on your platform and language environment, but in practice this rarely matters). To include newlines use the (.|\r?\n)* pattern which avoids the use of regex flags/modifiers and has good support across regex libraries.
  • ^: Matches only at the beginning of the string.
  • $: Matches only at the end of the string.
  • (...): Group a series of regular expressions into a single regular expression.
  • |: Matches either the regular expression preceding or following the | symbol.
  • [abc]: Matches any of the characters inside the square brackets.
  • [a-z]: Matches the range of characters.
  • [^abc]: Matches any character not listed.
  • [^a-z]: Matches any character outside of the range.
  • +: Matches one or more repetitions of the preceding regular expression.
  • *: Matches zero or more repetitions of the preceding regular expression.
  • ?: Matches zero or one repetitions of the preceding regular expression.
  • +?, *?, ??: The *, +, and ? qualifiers are all greedy; they match as much text as possible. Sometimes this behavior isn't desired and you want to match as few characters as possible.
  • (?!x), (?=x): Negative and positive lookahead.
  • {x}: Match exactly x occurrences of the preceding regular expression.
  • {x,y}: Match at least x and at most y occurrences of the preceding regular expression.
  • {x,}: Match x occurrences or more of the preceding regular expression.
  • {x}?, {x,y}?, {x,}?: Lazy versions of the above expressions.
  • Use only standard escapes like \n, \r, \t and keep in mind that you also need to do JSON escaping.

Example

The following example matches a simple North American telephone number with an optional area code:

schema
{ "type": "string", "pattern": "^(\\([0-9]{3}\\))?[0-9]{3}-[0-9]{4}$"}
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data
"555-1212"
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compliant to schema
data
"(888)555-1212"
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compliant to schema
data
"(888)555-1212 ext. 532"
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not compliant to schema
data
"(800)FLOWERS"
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not compliant to schema

The following example checks that the string starts with {{ and ends with }} and that it also allows multiline strings.

data
{ "type": "string", "pattern": "^\\{\\{(.|[\\r\\n])*\\}\\}$", }
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data
"{{ foo\nbar }}"
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data
"{ foo }"
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