Cisco Active Network Abstraction Customization User Guide, 3.6.4 - Regular Expressions [Cisco Active Network Abstraction]

Table Of Contents

Regular Expressions

Supported Syntax

Positional Operators

One-Character Operators

Character Class Operator

Branching (Alternation) Operator

Repeating Operators

Stingy (Minimal) Matching

Lookahead

Unsupported Syntax

Regular Expressions

This section is based on the documentation of the package GNU RegExp.

A regular expression consists of a character string in which some characters are given special meaning with regard to pattern matching. Regular expressions have been in use from the early days of computing, and provide a powerful and efficient way to parse, interpret, and search and replace text within an application.

Topics include:

•Supported Syntax

•Unsupported Syntax

Supported Syntax

Within a regular expression, the following characters have special meaning:

•Positional Operators

•One-Character Operators

•Character Class Operator

•Branching (Alternation) Operator

•Repeating Operators

•Stingy (Minimal) Matching

•Lookahead

Positional Operators

•^ matches at the beginning of a line.

•$ matches at the end of a line.

•\A matches the start of the entire string.

•\Z matches the end of the entire string.

•\b matches at a word break (Perl5 syntax only).

•\B matches at a nonword break (opposite of \b) (Perl5 syntax only).

•\< matches at the start of a word (egrep syntax only).

•\> matches at the end of a word (egrep syntax only).

One-Character Operators

•. matches any single character.

•\d matches any decimal digit.

•\D matches any nondigit.

•\n matches a newline character.

•\r matches a return character.

•\s matches any whitespace character.

•\S matches any nonwhitespace character.

•\t matches a horizontal tab character.

•\w matches any word (alphanumeric) character.

•\W matches any nonword (alphanumeric) character.

•\x matches the character x, if x is not one of the above listed escape sequences.

Character Class Operator

•[abc] matches any character in the set a, b, or c.

•[^abc] matches any character not in the set a, b, or c.

•[a-z] matches any character in the range a to z, inclusive.

•A leading or trailing dash is interpreted literally.

Within a character class expression, the following sequences have special meaning if the syntax bit RE_CHAR_CLASSES is on:

•[:alnum:] Any alphanumeric character

•[:alpha:] Any alphabetical character

•[:blank:] A space or horizontal tab

•[:cntrl:] A control character

•[:digit:] A decimal digit

•[:graph:] A nonspace, noncontrol character

•[:lower:] A lowercase letter

•[:print:] Same as graph, but also space and tab

•[:punct:] A punctuation character

•[:space:] Any whitespace character, including newline and return

•[:upper:] An uppercase letter

•[:xdigit:] A valid hexadecimal digit

Subexpressions and Back References

•(abc) matches whatever the expression abc would match, and saves it as a subexpression. Also used for grouping.

•(?:...) pure grouping operator, does not save contents

•(?#...) embedded comment, ignored by engine

•\n where 0 < n < 10, matches the same thing the nth subexpression matched.

Branching (Alternation) Operator

a|b matches whatever the expression a would match, or whatever the expression b would match.

Repeating Operators

These symbols operate on the previous atomic expression:

•? matches the preceding expression or the null string.

•* matches the null string or any number of repetitions of the preceding expression.

•+ matches one or more repetitions of the preceding expression.

•{m} matches exactly m repetitions of the one-character expression.

•{m,n} matches between m and n repetitions of the preceding expression, inclusive.

•{m,} matches m or more repetitions of the preceding expression.

Stingy (Minimal) Matching

If a repeating operator (above) is immediately followed by a question mark (?), the repeating operator stops at the smallest number of repetitions that can complete the rest of the match.

Lookahead

Lookahead refers to the ability to match part of an expression without consuming any of the input text. There are two variations:

•(?=foo) matches at any position where foo would match, but does not consume any characters of the input.

•(?!foo) matches at any position where foo would not match, but does not consume any characters of the input.

Unsupported Syntax

Some flavors of regular expression utilities support additional escape sequences. The following is not meant to be an exhaustive list. In the future, gnu.regexp might support some or all of the following:

•(?mods) inlined compilation/execution modifiers (Perl5)

•\G end of previous match (Perl5)

•[.symbol.] collating symbol in class expression (POSIX)

•[=class=] equivalence class in class expression (POSIX)

•s/foo/bar/ style expressions as in sed and awk (these can be accomplished through other means in the API).

	Cisco Active Network Abstraction Customization User Guide, 3.6.4
	Regular Expressions
Cisco Active Network Abstraction Customization User Guide, 3.6.4 Preface Overview Cisco ANA Overview Customizing Network Element Information Using the Soft Properties Manager Introducing the Cisco ANA Soft Properties Manager Getting Started with the Soft Properties Manager Soft Property Examples Parsing Operators/Rules Alarm Threshold Triggers Regular Expressions Using the Workflow Editor to Create Task Workflows Introducing the Cisco ANA Workflow Editor Working With the Cisco ANA Workflow Editor Getting Started with the Workflow Editor Managing Workflows Customizing the Workflow Editor Managing and Deploying Configuration Changes Using the Command Builder Introducing the Command Builder Getting Started with the Command Builder Creating an ANA Macro Language Command: An Example Running Command Scripts ANA Macro Language Bean Shell Commands Working with BQL Getting Started with Cisco BQL Understanding IMO IMO Specification BQL Generic Commands Encrypted SSL Sockets Detailed BQL Errors Catalog and Examples Best Practices for Integration BQL Parsing Index	Download this chapter Regular Expressions Download the complete book PDF of Cisco Active Network Abstraction Customization User Guide, 3.6.4 (PDF - 4 MB) Table Of Contents Regular Expressions Supported Syntax Positional Operators One-Character Operators Character Class Operator Branching (Alternation) Operator Repeating Operators Stingy (Minimal) Matching Lookahead Unsupported Syntax Regular Expressions This section is based on the documentation of the package GNU RegExp. A regular expression consists of a character string in which some characters are given special meaning with regard to pattern matching. Regular expressions have been in use from the early days of computing, and provide a powerful and efficient way to parse, interpret, and search and replace text within an application. Topics include: •Supported Syntax •Unsupported Syntax Supported Syntax Within a regular expression, the following characters have special meaning: •Positional Operators •One-Character Operators •Character Class Operator •Branching (Alternation) Operator •Repeating Operators •Stingy (Minimal) Matching •Lookahead Positional Operators •^ matches at the beginning of a line. •$ matches at the end of a line. •\A matches the start of the entire string. •\Z matches the end of the entire string. •\b matches at a word break (Perl5 syntax only). •\B matches at a nonword break (opposite of \b) (Perl5 syntax only). •\< matches at the start of a word (egrep syntax only). •\> matches at the end of a word (egrep syntax only). One-Character Operators •. matches any single character. •\d matches any decimal digit. •\D matches any nondigit. •\n matches a newline character. •\r matches a return character. •\s matches any whitespace character. •\S matches any nonwhitespace character. •\t matches a horizontal tab character. •\w matches any word (alphanumeric) character. •\W matches any nonword (alphanumeric) character. •\x matches the character x, if x is not one of the above listed escape sequences. Character Class Operator •[abc] matches any character in the set a, b, or c. •[^abc] matches any character not in the set a, b, or c. •[a-z] matches any character in the range a to z, inclusive. •A leading or trailing dash is interpreted literally. Within a character class expression, the following sequences have special meaning if the syntax bit RE_CHAR_CLASSES is on: •[:alnum:] Any alphanumeric character •[:alpha:] Any alphabetical character •[:blank:] A space or horizontal tab •[:cntrl:] A control character •[:digit:] A decimal digit •[:graph:] A nonspace, noncontrol character •[:lower:] A lowercase letter •[:print:] Same as graph, but also space and tab •[:punct:] A punctuation character •[:space:] Any whitespace character, including newline and return •[:upper:] An uppercase letter •[:xdigit:] A valid hexadecimal digit Subexpressions and Back References •(abc) matches whatever the expression abc would match, and saves it as a subexpression. Also used for grouping. •(?:...) pure grouping operator, does not save contents •(?#...) embedded comment, ignored by engine •\n where 0 < n < 10, matches the same thing the nth subexpression matched. Branching (Alternation) Operator a\|b matches whatever the expression a would match, or whatever the expression b would match. Repeating Operators These symbols operate on the previous atomic expression: •? matches the preceding expression or the null string. •* matches the null string or any number of repetitions of the preceding expression. •+ matches one or more repetitions of the preceding expression. •{m} matches exactly m repetitions of the one-character expression. •{m,n} matches between m and n repetitions of the preceding expression, inclusive. •{m,} matches m or more repetitions of the preceding expression. Stingy (Minimal) Matching If a repeating operator (above) is immediately followed by a question mark (?), the repeating operator stops at the smallest number of repetitions that can complete the rest of the match. Lookahead Lookahead refers to the ability to match part of an expression without consuming any of the input text. There are two variations: •(?=foo) matches at any position where foo would match, but does not consume any characters of the input. •(?!foo) matches at any position where foo would not match, but does not consume any characters of the input. Unsupported Syntax Some flavors of regular expression utilities support additional escape sequences. The following is not meant to be an exhaustive list. In the future, gnu.regexp might support some or all of the following: •(?mods) inlined compilation/execution modifiers (Perl5) •\G end of previous match (Perl5) •[.symbol.] collating symbol in class expression (POSIX) •[=class=] equivalence class in class expression (POSIX) •s/foo/bar/ style expressions as in sed and awk (these can be accomplished through other means in the API).
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