Standard operators
Anchoring
Most regular expression engines allow you to match any part of a string. If you want the regexp pattern to start at the beginning of the string or finish at the end of the string, then you have to anchor it specifically, using ^ to indicate the beginning or $ to indicate the end.
Howeer, Lucene’s patterns are always anchored. The pattern provided must match the entire string. For string abcde:
ab.* # match
abcd # no match
Allowed characters
Any Unicode characters may be used in the pattern, but certain characters are reserved and must be escaped. The standard reserved characters are:
. ? + * | { } [ ] ( ) " \
Any reserved character can be escaped with a backslash \* including a literal backslash character: \\
Additionally, any characters (except double quotes) are interpreted literally when surrounded by double quotes:
john"@smith.com"
Match any character
The period . can be used to represent any character. For string abcde:
ab... # match
a.c.e # match
One-or-more
The plus sign + can be used to repeat the preceding shortest pattern once or more times. For string aaabbb:
a+b+ # match
aa+bb+ # match
a+.+ # match
aa+bbb+ # match
Zero-or-more
The asterisk * can be used to match the preceding shortest pattern zero-or-more times. For string aaabbb:
a*b* # match
a*b*c* # match
.*bbb.* # match
aaa*bbb* # match
Zero-or-one
The question mark ? makes the preceding shortest pattern optional. It matches zero or one times. For string aaabbb:
aaa?bbb? # match
aaaa?bbbb? # match
.....?.? # match
aa?bb? # no match
Min-to-max
Curly brackets {} can be used to specify a minimum and (optionally) a maximum number of times the preceding shortest pattern can repeat. The allowed forms are:
{5} # repeat exactly 5 times
{2,5} # repeat at least twice and at most 5 times
{2,} # repeat at least twice
For string aaabbb:
a{3}b{3} # match
a{2,4}b{2,4} # match
a{2,}b{2,} # match
.{3}.{3} # match
a{4}b{4} # no match
a{4,6}b{4,6} # no match
a{4,}b{4,} # no match
Grouping
Parentheses () can be used to form sub-patterns. The quantity operators listed above operate on the shortest previous pattern, which can be a group. For string ababab:
(ab)+ # match
ab(ab)+ # match
(..)+ # match
(...)+ # no match
(ab)* # match
abab(ab)? # match
ab(ab)? # no match
(ab){3} # match
(ab){1,2} # no match
Alternation
The pipe symbol | acts as an OR operator. The match will succeed if the pattern on either the left-hand side OR the right-hand side matches. The alternation applies to the longest pattern, not the shortest. For string aabb:
aabb|bbaa # match
aacc|bb # no match
aa(cc|bb) # match
a+|b+ # no match
a+b+|b+a+ # match
a+(b|c)+ # match
Character classes
Ranges of potential characters may be represented as character classes by enclosing them in square brackets []. A leading ^ negates the character class. The allowed forms are:
[abc] # 'a' or 'b' or 'c'
[a-c] # 'a' or 'b' or 'c'
[-abc] # '-' or 'a' or 'b' or 'c'
[abc\-] # '-' or 'a' or 'b' or 'c'
[^abc] # any character except 'a' or 'b' or 'c'
[^a-c] # any character except 'a' or 'b' or 'c'
[^-abc] # any character except '-' or 'a' or 'b' or 'c'
[^abc\-] # any character except '-' or 'a' or 'b' or 'c'
Note that the dash - indicates a range of characters, unless it is the first character or if it is escaped with a backslash.
For string abcd:
ab[cd]+ # match
[a-d]+ # match
[^a-d]+ # no match
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