Regular Expressions

Regular expressions provide a powerful way of matching patterns, in essence anything other than a simple string literal.

When you enter a regular expression in a PhixFlow field, remember that it must be contained inside "quotes", except where you are using PhixFlow variables that contain strings, or functions that return strings.

"inputFile_[0-9]{3}\\.txt"

will match data - in this case file names - that have the format inputFile_NNN.txt, where N are digits. E.g. inputFile_034.txt.

"inputFile_" + today() + "\\.txt"

will match data - in this case file names - that have the format inputFile_YYYYMMDD.txt, where YYYYMMDD is the current date. E.g. inputFile_20130828.txt.

"inputFile_" + $fileSeq + "\\.txt"

will match data - in this case file names - that have the format inputFile_$fileSeq.txt. E.g. if $fileSeq="034", this will match inputFile_034.txt.

Regular expressions are seen throughout many languages (C, Java, Perl) and unix shells. PhixFlow regular expressions follow the common rules of POSIX regular expressions to a great extent; specification for the elements of regular expressions are given below. Useful examples of regular expressions are found in replaceAll, replaceFirst, matches.

In PhixFlow, to escape a character you must use two backslashes: \\, e.g. \\n for a new line. To match a backslash in the data you are matching, you will need four backslashes: \\\\ in your regular expression. See below for details.

Regular expression constructs, and what they match

Construct	Matches
Characters
x	The character x
\\\\	The backslash character
\\/	The forward slash character
\\\"	The double quote character
\\0n	The character with octal value 0n (0 <= n <= 7)
\\0nn	The character with octal value 0nn (0 <= n <= 7)
\\0mnn	The character with octal value 0mnn (0 <= m <= 3, 0 <= n <= 7)
\\xhh	The character with hexadecimal value 0xhh
\uhhhh	The character with hexadecimal value 0xhhhh
\\t	The tab character ('\u0009')
\\n	The newline (line feed) character ('\u000A')
\\r	The carriage-return character ('\u000D')
\\f	The form-feed character ('\u000C')
\\a	The alert (bell) character ('\u0007')
\\e	The escape character ('\u001B')
\\cx	The control character corresponding to x
Character classes
[abc]	a, b, or c (simple class)
[^abc]	Any character except a, b, or c (negation)
[a-zA-Z]	a through z or A through Z, inclusive (range)
[a-d[m-p]]	a through d, or m through p: [a-dm-p] (union)
[a-z&&[def]]	d, e, or f (intersection)
[a-z&&[^bc]]	a through z, except for b and c: [ad-z] (subtraction)
[a-z&&[^m-p]]	a through z, and not m through p: [a-lq-z](subtraction)
Predefined character classes
.	Any character (may or may not match line terminators)
\\d	A digit: [0-9]
\\D	A non-digit: [^0-9]
\\s	A whitespace character: [ \\t\\n\\x0B\\f\\r]
\\S	A non-whitespace character: [^\\s]
\\w	A word character: [a-zA-Z_0-9]
\\W	A non-word character: [^\\w]
POSIX character classes (US-ASCII only)
\\p{Lower}	A lower-case alphabetic character: [a-z]
\\p{Upper}	An upper-case alphabetic character:[A-Z]
\\p{ASCII}	All ASCII:[\\x00-\\x7F]
\\p{Alpha}	An alphabetic character:[\\p{Lower}\\p{Upper}]
\\p{Digit}	A decimal digit: [0-9]
\\p{Alnum}	An alphanumeric character:[\\p{Alpha}\\p{Digit}]
\\p{Punct}	Punctuation: One of !"#$%&'()*+,-./:;<=>?@[\]^_`{\|}~
\\p{Graph}	A visible character: [\\p{Alnum}\\p{Punct}]
\\p{Print}	A printable character: [\\p{Graph}]
\\p{Blank}	A space or a tab: [ \\t]
\\p{Cntrl}	A control character: [\\x00-\\x1F\\x7F]
\\p{XDigit}	A hexadecimal digit: [0-9a-fA-F]
\\p{Space}	A whitespace character: [ \\t\\n\\x0B\\f\\r]
Classes for Unicode blocks and categories
\\p{InGreek}	A character in the Greek block (simple block)
\\p{Lu}	An uppercase letter (simple category)
\\p{Sc}	A currency symbol
\\P{InGreek}	Any character except one in the Greek block (negation)
[\\p{L}&&[^\\p{Lu}]]	Any letter except an uppercase letter (subtraction)
Boundary matchers
^	The beginning of a line
$	The end of a line
\\b	A word boundary
\\B	A non-word boundary
\\A	The beginning of the input
\\G	The end of the previous match
\\Z	The end of the input but for the final terminator, if any
\\z	The end of the input
Greedy quantifiers
X?	X, once or not at all
X*	X, zero or more times
X+	X, one or more times
X{n}	X, exactly n times
X{n,}	X, at least n times
X{n,m}	X, at least n but not more than m times
Reluctant quantifiers
X??	X, once or not at all
X*?	X, zero or more times
X+?	X, one or more times
X{n}?	X, exactly n times
X{n,}?	X, at least n times
X{n,m}?	X, at least n but not more than m times
Possessive quantifiers
X?+	X, once or not at all
X*+	X, zero or more times
X++	X, one or more times
X{n}+	X, exactly n times
X{n,}+	X, at least n times
X{n,m}+	X, at least n but not more than m times
Logical operators
XY	X followed by Y
X\|Y	Either X or Y
(X)	X, as a capturing group
Back references
$n	Whatever the n^th capturing group matched
Quotation
\\	Nothing, but quotes the following character
\\Q	Nothing, but quotes all characters until \\E
\\E	Nothing, but ends quoting started by \\Q
Special constructs (non-capturing)
(?:X)	X, as a non-capturing group
(?idmsux-idmsux)	Nothing, but turns match flags on - off
(?idmsux-idmsux:X)	X, as a non-capturing group with the given flags on - off
(?=X)	X, via zero-width positive lookahead
(?!X)	X, via zero-width negative lookahead
(?<=X)	X, via zero-width positive lookbehind
(?<!X)	X, via zero-width negative lookbehind
(?>X)	X, as an independent, non-capturing group

Backslashes, escapes, and quoting

A double backslash \\ either makes an alphanumeric character a contruct (e.g. \\n means newline), or allows a special character to be quoted (e.g. use \\{ if you want to match the { character). If you escape an alphabetic character that is not a construct when escaped, you will get an error.

Line terminators

A line terminator is a one- or two-character sequence that marks the end of a line of the input character sequence. The following are recognized as line terminators:

A newline (line feed) character ('\\n'),
A carriage-return character followed immediately by a newline character ("\\r\\n"),
A standalone carriage-return character ('\\r'),
A next-line character ('\\u0085'),
A line-separator character ('\\u2028'), or
A paragraph-separator character ('\\u2029).

Groups and capturing

Capturing groups are numbered by counting their opening parentheses from left to right. In the expression ((A)(B(C))), for example, there are four such groups:

1	((A)(B(C)))
2	(A)
3	(B(C))
4	(C)

Group zero always stands for the entire expression.

During a match, each sub-sequence of the input sequence that matches a group is saved. The captured sub-sequence may be used later in the expression, via a back reference. In PhixFlow, a back reference has the format $n, where n is the number of the capturing group. See examples for replaceFirst.

The captured input associated with a group is always the sub-sequence that the group most recently matched. If a group is evaluated a second time because of a quantifier then its previously captured value, if any, will be retained if the second evaluation fails. Matching the string "aba" against the expression (a(b)?)+, for example, leaves group two set to "b". All captured input is discarded at the beginning of each match.

Groups beginning with (? are pure, non-capturing groups that do not capture text and do not count towards the group total.