Regular Expression

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Introduction

Using a Regular Expression string in a FIND, CHANGE, JOIN, EXCLUDE or similar command provides you with a powerful tool for searching. If you have never used regular expressions they may appear quite complex. However many users will already be familiar with them from their use on other systems like Linux or Unix.

Note: Users familiar with regular expressions should be aware that there are many variants of regular expression syntax implemented in different systems and applications, some with fairly subtle differences. The description below describes the regular expression engine supported by SPFLite. The RegEx engine chosen for SPFLite is PCRE (Perl Compatible Regular Expression). This engine is widely used and supports a robust RegEx syntax. Because regular expressions can be complex, SPFLite provides a small program to allow you to experiment with Regular Expressions and become familiar with their use. See Using the SPFTest Program for details.

There are several sites on the web providing assistance in learning about and testing Regular Expressions. One such tutorial can be found at www.regexlab.com .

The regular expression must be enclosed in quotes (single, double, or accent) preceded or followed by the character R.

Examples:

R'abc$'

'abc$'R

SubTopics

PCRE Regular Expression Syntax Summary

This PCRE Syntax documentation courtesy of www.pcre.org - Copyright © 1997-2014 University of Cambridge. This is a summary only. The full description can be found at http://www.pcre.org/original/doc/html/pcrepattern.html

QUOTING

\x where x is non-alphanumeric is a literal x

\Q...\E treat enclosed characters as literal

Note that in PCRE, the code \Q differs from prior SPFLite RegEx usage of \q.

See Compatibility Considerations below for more information.

CHARACTERS

\a alarm, that is, the BEL character (hex 07)

\cx "control-x", where x is any ASCII character

\e escape (hex 1B)

\f form feed (hex 0C)

\n newline (hex 0A)

\r carriage return (hex 0D)

\t tab (hex 09)

\0dd character with octal code 0dd

\ddd character with octal code ddd, or backreference

\o{ddd..} character with octal code ddd..

\xhh character with hex code hh

\x{hhh..} character with hex code hhh..

Note that \0dd is always an octal code, and that \8 and \9 are the literal characters "8" and "9".

Note that in PCRE, the code \c differs from prior SPFLite RegEx usage.

See Compatibility Considerations below for more information.

CHARACTER TYPES

These codes represent any character except for newline. In "dotall mode", these codes represent any character whatsoever.

\C one data unit, even in UTF mode (best avoided)

\d a decimal digit

\D a character that is not a decimal digit

\h a horizontal white space character

\H a character that is not a horizontal white space character

\N a character that is not a newline

\p{xx} a character with the xx property

\P{xx} a character without the xx property

\R a newline sequence

\s a white space character

\S a character that is not a white space character

\v a vertical white space character

\V a character that is not a vertical white space character

\w a "word" character

\W a "non-word" character

\X a Unicode extended grapheme cluster

By default, \d, \s, and \w match only ASCII characters.

Note that in PCRE, the code \s differs from prior SPFLite RegEx usage.

See Compatibility Considerations below for more information.

GENERAL CATEGORY PROPERTIES FOR \p and \P

C Other

Cc Control

Cf Format

Cn Unassigned

Co Private use

Cs Surrogate

L Letter

Ll Lower case letter

Lm Modifier letter

Lo Other letter

Lt Title case letter

Lu Upper case letter

L& Ll, Lu, or Lt

M Mark

Mc Spacing mark

Me Enclosing mark

Mn Non-spacing mark

N Number

Nd Decimal number

Nl Letter number

No Other number

P Punctuation

Pc Connector punctuation

Pd Dash punctuation

Pe Close punctuation

Pf Final punctuation

Pi Initial punctuation

Po Other punctuation

Ps Open punctuation

S Symbol

Sc Currency symbol

Sk Modifier symbol

Sm Mathematical symbol

So Other symbol

Z Separator

Zl Line separator

Zp Paragraph separator

Zs Space separator

PCRE SPECIAL CATEGORY PROPERTIES FOR \p and \P

Xan Alphanumeric: union of properties L and N

Xps POSIX space: property Z or tab, NL, VT, FF, CR

Xsp Perl space: property Z or tab, NL, VT, FF, CR

Xuc Univerally-named character: one that can be

represented by a Universal Character Name

Xwd Perl word: property Xan or underscore

CHARACTER CLASSES

[...] positive character class

[^...] negative character class

[x-y] range (can be used for hex characters)

[[:xxx:]] positive POSIX named set; see list below

[[:^xxx:]] negative POSIX named set; see list below

xxx can be one of the following:

alnum alphanumeric

alpha alphabetic

ascii characters in the range of 0 to 127 (\x00 to \x7F)

blank space or tab

cntrl control character

digit decimal digit

graph printing, excluding space

lower lower case letter

print printing, including space

punct printing, excluding alphanumeric

space white space

upper upper case letter

word same as \w

xdigit hexadecimal digit

QUANTIFIERS

? 0 or 1, greedy

?+ 0 or 1, possessive

?? 0 or 1, lazy

* 0 or more, greedy

*+ 0 or more, possessive

*? 0 or more, lazy

+ 1 or more, greedy

++ 1 or more, possessive

+? 1 or more, lazy

{n} exactly n

{n,m} at least n, no more than m, greedy

{n,m}+ at least n, no more than m, possessive

{n,m}? at least n, no more than m, lazy

{n,} n or more, greedy

{n,}+ n or more, possessive

{n,}? n or more, lazy

Note that in PCRE, the quantifier code ? may be used in some cases like the code \s from prior SPFLite RegEx usage.

See Compatibility Considerations below for more information.

ANCHORS AND SIMPLE ASSERTIONS

\b word boundary

\B not a word boundary

^ start of subject

also after internal newline in multiline mode

\A start of subject

$ end of subject

also before newline at end of subject

also before internal newline in multiline mode

\Z end of subject

also before newline at end of subject

\z end of subject

\G first matching position in subject

MATCH POINT RESET

\K reset start of match

\K is honored in positive assertions, but ignored in negative ones.

ALTERNATION

expr|expr|expr...

CAPTURING

(...) capturing group

(?<name>...) named capturing group (Perl)

(?'name'...) named capturing group (Perl)

(?P<name>...) named capturing group (Python)

(?:...) non-capturing group

(?|...) non-capturing group; reset group numbers for

capturing groups in each alternative

ATOMIC GROUPS

(?>...) atomic, non-capturing group

COMMENT

(?#....) comment (not nestable)

OPTION SETTING

(?i) caseless

(?J) allow duplicate names

(?m) multiline

(?s) single line (dotall)

(?U) default ungreedy (lazy)

(?x) extended (ignore white space)

(?-...) unset option(s)

The following are recognized only at the very start of a pattern or after one of the newline or \R options with similar syntax. More than one of them may appear.

(*LIMIT_MATCH=d) set the match limit to d (decimal number)

(*LIMIT_RECURSION=d) set the recursion limit to d (decimal number)

(*NO_AUTO_POSSESS) no auto-possessification (PCRE_NO_AUTO_POSSESS)

(*NO_START_OPT) no start-match optimization (PCRE_NO_START_OPTIMIZE)

(*UTF8) set UTF-8 mode: 8-bit library (PCRE_UTF8)

(*UTF16) set UTF-16 mode: 16-bit library (PCRE_UTF16)

(*UTF32) set UTF-32 mode: 32-bit library (PCRE_UTF32)

(*UTF) set appropriate UTF mode for the library in use

(*UCP) set PCRE_UCP (use Unicode properties for \d etc)

Note that LIMIT_MATCH and LIMIT_RECURSION can only reduce the value of the limits set by the caller of pcre_exec(), not increase them.

NEWLINE CONVENTION

These are recognized only at the very start of the pattern or after option settings with a similar syntax.

(*CR) carriage return only

(*LF) linefeed only

(*CRLF) carriage return followed by linefeed

(*ANYCRLF) all three of the above

(*ANY) any Unicode newline sequence

WHAT \R MATCHES

These are recognized only at the very start of the pattern or after option setting with a similar syntax.

(*BSR_ANYCRLF) CR, LF, or CRLF

(*BSR_UNICODE) any Unicode newline sequence

Note: Be careful not to confuse \R with \r. The code \r only means a carriage return character (\x0D), while the meaning of \R depends on the settings above.

LOOKAHEAD AND LOOKBEHIND ASSERTIONS

(?=...) positive look ahead

(?!...) negative look ahead

(?<=...) positive look behind

(?<!...) negative look behind

Each top-level branch of a look behind must be of a fixed length.

BACKREFERENCES

\n reference by number (can be ambiguous)

\gn reference by number

\g{n} reference by number

\g{-n} relative reference by number

\k<name> reference by name (Perl)

\k'name' reference by name (Perl)

\g{name} reference by name (Perl)

\k{name} reference by name (.NET)

(?P=name) reference by name (Python)

SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)

(?R) recurse whole pattern

(?n) call subpattern by absolute number

(?+n) call subpattern by relative number

(?-n) call subpattern by relative number

(?&name) call subpattern by name (Perl)

(?P>name) call subpattern by name (Python)

\g<name> call subpattern by name (Oniguruma)

\g'name' call subpattern by name (Oniguruma)

\g<n> call subpattern by absolute number (Oniguruma)

\g'n' call subpattern by absolute number (Oniguruma)

\g<+n> call subpattern by relative number (PCRE extension)

\g'+n' call subpattern by relative number (PCRE extension)

\g<-n> call subpattern by relative number (PCRE extension)

\g'-n' call subpattern by relative number (PCRE extension)

CONDITIONAL PATTERNS

(?(condition)yes-pattern)

(?(condition)yes-pattern|no-pattern)

(?(n)... absolute reference condition

(?(+n)... relative reference condition

(?(-n)... relative reference condition

(?(<name>)... named reference condition (Perl)

(?('name')... named reference condition (Perl)

(?(name)... named reference condition (PCRE)

(?(R)... overall recursion condition

(?(Rn)... specific group recursion condition

(?(R&name)... specific recursion condition

(?(DEFINE)... define subpattern for reference

(?(assert)... assertion condition

BACKTRACKING CONTROL

The following act immediately they are reached:

(*ACCEPT) force successful match

(FAIL) force backtrack; synonym (F)

(MARK:NAME) set name to be passed back; synonym (:NAME)

The following act only when a subsequent match failure causes a backtrack to reach them. They all force a match failure, but they differ in what happens afterwards. Those that advance the start-of-match point do so only if the pattern is not anchored.

(*COMMIT) overall failure, no advance of starting point

(*PRUNE) advance to next starting character

(PRUNE:NAME) equivalent to (MARK:NAME)(*PRUNE)

(*SKIP) advance to current matching position

(*SKIP:NAME) advance to position corresponding to an earlier

(MARK:NAME); if not found, the (SKIP) is ignored

(*THEN) local failure, backtrack to next alternation

(THEN:NAME) equivalent to (MARK:NAME)(*THEN)

CALLOUTS

(?C) callout

(?Cn) callout with data n

Performance Considerations

Be aware that the *, + and ? meta-characters can cause the regular expression engine to perform backtracking, which can cause its pattern-matching to run a little slower. As with all regular expressions, performance is dependent on file size and the complexity of the expression.

Examples of Using RegEx

Given a file with lines:

"Blah blah blah blah"

"Please send email to FredFarkle@mydomain.com"

"Thank you very much."

The line with the email address could be found with:

FIND R"([a-z0-9._/+-]+)(@[a-z0-9.-]+)"

Given the lines:

"Balance due by 15th of the month"

"Amount owed: $42.75 and is overdue!"

The line with the Balance amount could be found with:

FIND R"\$[0-9.,]+"