Regular expressions

Regular expressions can be used to test if a text contains a specific text or more general whether a given text matches a defined pattern.

Basic pattern examples:

Test.*	This pattern matches a text that starts with Test with an unlimited number of successive characters, for example Test, Testabc but not abcTest, 123Test123
Test.+	This pattern matches a text that starts with Test with an unlimited number of successive characters but must contain at least one character after Test. For example TestX but not Test
[a-c]{3}	This pattern matches a text that consists of exactly three characters a to c, for example: aaa, abc, cba but not xyz.
\d{3}.*	This pattern matches a text that starts with three digits, for example 123abc, 123456 but not 12abc or abc123.

Automagic supports regular expressions with following functions in action Script or condition Expression:

• Boolean matches(String s, String pattern)
  Returns whether the string s matches the regular expression pattern.
• Boolean matches(String s, String pattern, List groups)
  Returns whether the string s matches the regular expression pattern and fills the captured groups into the existing list groups.
• List findAll(String s, String pattern)
  Returns a list of all matched values in s of regex pattern.
• String replaceAll(String s, String regex, String replacement)
  Returns a modified string by replacing all substrings matching regex with replacement in string s.
• List split(String s, String pattern)
  Splits the string s into a list of strings by using the regular expression pattern as the delimiter.

Examples for function Boolean matches(String s, String pattern)

• Test if a text contains the word test:
  result = matches("this is a test", ".*test.*")
  
• Test if a text contains at least three digits at the beginning:
  result = matches("1234567", "\\d{3}.*")
  The regular expression would only require one backslash by itself, but one backslash has to be escaped with one additional backslash in a string in a script of Automagic.

Examples for function Boolean matches(String s, String pattern, List groups)

• Test if a text contains a number and store the first number in the list groups:
  groups = newList(); result = matches("contact 123456 called", "\\D*(\\d*).*");
  The list groups will contain the two elements "contact 123456 called" and "123456".

Examples for function List findAll(String s, String pattern)

• Returns a list of all matched values in s of regex pattern.:
  result = findAll("contact 123456 calls at 8 o'clock", "\\d*");
  The list groups will contain the two elements "123456" and "8".

Examples for function String replaceAll(String s, String regex, String replacement)

• Remove all numbers from a text:
  result = replaceAll("contact 123456 called", "\\d", "");
result will contain "contact called".
• Remove consecutive whitespace characters and replace with one space character:
  result = replaceAll("a b c", "\\s+", " ");
result will contain "a b c".
• Separate the characters in a text by spaces:
  result = replaceAll("1234567", "(.)", "$1 ");
result will contain "1 2 3 4 5 6 7 ".
  $1 refers to the text matched in the first capturing group enclosed by parenthesis.
• Insert different delimiters between characters:
  result = replaceAll("123456", "(.)(.)", "$1/$2-");
result will contain "1/2-3/4-5/6-".
  $1 refers to the text matched in the first capturing group enclosed by parenthesis, $2 refers to the second capturing group enclosed by parenthesis.

Examples for function List split(String s, String pattern)

• Split the text on every colon to create a list of tokens:
  result = split("this:is:a:test", ":");
  The list result will contain the four elements "this", "is", "a" and "test".
• Split a text into a list of words:
  result = split("this is a:test", "\\W");
  The list result will contain the four elements "this", "is", "a" and "test".

Android regular expressions

Automagic uses the built-in classes of Android to support regular expressions. Android API online documentation

The following documentation is an extract of the most important features of the regular expression syntax.

Escape sequences

\	Quote the following metacharacter (so \. matches a literal .).
\Q	Quote all following metacharacters until \E.
\E	Stop quoting metacharacters (started by \Q).
\\	A literal backslash.
\uhhhh	The Unicode character U+hhhh (in hex).
\xhh	The Unicode character U+00hh (in hex).
\cx	The ASCII control character ^x (so \cH would be ^H, U+0008).
\a	The ASCII bell character (U+0007).
\e	The ASCII ESC character (U+001b).
\f	The ASCII form feed character (U+000c).
\n	The ASCII newline character (U+000a).
\r	The ASCII carriage return character (U+000d).
\t	The ASCII tab character (U+0009).

Character classes

It's possible to construct arbitrary character classes using set operations:

[abc]	Any one of a, b, or c. (Enumeration.)
[a-c]	Any one of a, b, or c. (Range.)
[^abc]	Any character except a, b, or c. (Negation.)
[[a-f][0-9]]	Any character in either range. (Union.)
[[a-z]&&[jkl]]	Any character in both ranges. (Intersection.)

Most of the time, the built-in character classes are more useful:

\d	Any digit character (see note below).
\D	Any non-digit character (see note below).
\s	Any whitespace character (see note below).
\S	Any non-whitespace character (see note below).
\w	Any word character (see note below).
\W	Any non-word character (see note below).
\p{NAME}	Any character in the class with the given NAME.
\P{NAME}	Any character not in the named class.

Note that these built-in classes don't just cover the traditional ASCII range. For example, \w is equivalent to the character class [\p{Ll}\p{Lu}\p{Lt}\p{Lo}\p{Nd}]. For more details see Unicode TR-18, and bear in mind that the set of characters in each class can vary between Unicode releases. If you actually want to match only ASCII characters, specify the explicit characters you want; if you mean 0-9 use [0-9] rather than \d, which would also include Gurmukhi digits and so forth.

Quantifiers

Quantifiers match some number of instances of the preceding regular expression.

*	Zero or more.
?	Zero or one.
+	One or more.
{n}	Exactly n.
{n,}	At least n.
{n,m}	At least n but not more than m.

Quantifiers are "greedy" by default, meaning that they will match the longest possible input sequence. There are also non-greedy quantifiers that match the shortest possible input sequence. They're same as the greedy ones but with a trailing ?:

*?	Zero or more (non-greedy).
??	Zero or one (non-greedy).
+?	One or more (non-greedy).
{n}?	Exactly n (non-greedy).
{n,}?	At least n (non-greedy).
{n,m}?	At least n but not more than m (non-greedy).

Quantifiers allow backtracking by default. There are also possessive quantifiers to prevent backtracking. They're same as the greedy ones but with a trailing +:

*+	Zero or more (possessive).
?+	Zero or one (possessive).
++	One or more (possessive).
{n}+	Exactly n (possessive).
{n,}+	At least n (possessive).
{n,m}+	At least n but not more than m (possessive).

Zero-width assertions

^	At beginning of line.
$	At end of line.
\A	At beginning of input.
\b	At word boundary.
\B	At non-word boundary.
\G	At end of previous match.
\z	At end of input.
\Z	At end of input, or before newline at end.

Look-around assertions

Look-around assertions assert that the subpattern does (positive) or doesn't (negative) match after (look-ahead) or before (look-behind) the current position, without including the matched text in the containing match. The maximum length of possible matches for look-behind patterns must not be unbounded.

(?=a)	Zero-width positive look-ahead.
(?!a)	Zero-width negative look-ahead.
(?<=a)	Zero-width positive look-behind.
(?<!a)	Zero-width negative look-behind.

Groups

(a)	A capturing group.
(?:a)	A non-capturing group.
(?>a)	An independent non-capturing group. (The first match of the subgroup is the only match tried.)
\n	The text already matched by capturing group n.

See group() for details of how capturing groups are numbered and accessed.

Operators

ab	Expression a followed by expression b.
a|b	Either expression a or expression b.

Flags

(?dimsux-dimsux:a)	Evaluates the expression a with the given flags enabled/disabled.
(?dimsux-dimsux)	Evaluates the rest of the pattern with the given flags enabled/disabled.

The flags are:

i	CASE_INSENSITIVE	case insensitive matching
d	UNIX_LINES	only accept '\n' as a line terminator
m	MULTILINE	allow ^ and $ to match beginning/end of any line
s	DOTALL	allow . to match '\n' ("s" for "single line")
u	UNICODE_CASE	enable Unicode case folding
x	COMMENTS	allow whitespace and comments