Difference: RegularExpression (1 vs. 11)

Revision 112016-02-23 - TWikiContributor

 

Regular Expressions

Introduction

Regular expressions (REs), unlike simple queries, allow you to search for text which matches a particular pattern.

Changed:
<
<
REs are similar to (but more poweful than) the "wildcards" used in the command-line interfaces found in operating systems such as Unix and MS-DOS. REs are used by sophisticated search engines, as well as by many Unix-based languages and tools ( e.g., awk, grep, lex, perl, and sed ).
>
>
REs are similar to (but more powerful than) the "wildcards" used in the command-line interfaces found in operating systems such as Unix and MS-DOS. REs are used by sophisticated search engines, as well as by many Unix-based languages and tools ( e.g., awk, grep, lex, perl, and sed ).
 

Examples

Changed:
<
<
compan(y|ies) Search for company, companies
(peter|paul) Search for peter, paul
>
>
compan(y|ies) Search for company, companies
(peter|paul) Search for peter, paul
 
bug* Search for bug, bugg, buggg or simply bu (a star matches zero or more instances of the previous character)
bug.* Search for bug, bugs, bugfix (a dot-star matches zero or more instances of any character)
[Bb]ag Search for Bag, bag
b[aiueo]g Second letter is a vowel. Matches bag, bug, big
b.g Second letter is any letter. Matches also b&g
[a-zA-Z] Matches any one letter (but not a number or a symbol)
[^0-9a-zA-Z] Matches any symbol (but not a number or a letter)
[A-Z][A-Z]* Matches one or more uppercase letters
[0-9]{3}-[0-9]{2}-[0-9]{4} US social security number, e.g. 123-45-6789
Chart;PNG;!JPG Search for topics containing the words Chart and PNG and not JPG. The ";" and "!" are TWiki-specific operators and are not part of regular expression

Searches with "and" combinations

A TWiki type="regex" SEARCH introduces two special characters to regular expressions:

  • The semicolon ";" is an AND-operator.
    Example search for "form" and "template": form;template
  • The exclamation point "!" as a NOT-operator.
    Example search for "soap" and "wsdl" and not "shampoo": soap;wsdl;!shampoo

TWiki also supports a SQL-like query search where you can literally use AND and NOT operators.

Use Google if your TWiki site is public. Example search for "form" and "template" at TWiki.org: site:twiki.org +form +template

Advanced

Here is stuff for our UNIX freaks: (copied from 'man egrep')

A regular expression is a pattern that describes a set of strings. Regular expressions are constructed analogously to arithmetic expressions, by using various operators to combine smaller expressions.

The fundamental building blocks are the regular expressions that match a single character. Most characters, including all letters and digits, are regular expressions that match themselves. Any metacharacter with special meaning may be quoted by preceding it with a backslash.

A bracket expression is a list of characters enclosed by [ and ]. It matches any single character in that list; if the first character of the list is the caret ^ then it matches any character not in the list. For example, the regular expression [0123456789] matches any single digit.

Within a bracket expression, a range expression consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, inclusive, using the locale's collating sequence and character set. For example, in the default C locale, [a-d] is equivalent to [abcd]. Many locales sort characters in dictionary order, and in these locales [a-d] is typically not equivalent to [abcd]; it might be equivalent to [aBbCcDd], for example.

Finally, certain named classes of characters are predefined within bracket expressions, as follows. Their names are self explanatory, and they are [:alnum:], [:alpha:], [:cntrl:], [:digit:], [:graph:], [:lower:], [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:]. For example, [[:alnum:]] means [0-9A-Za-z], except the latter form depends upon the C locale and the ASCII character encoding, whereas the former is independent of locale and character set. (Note that the brackets in these class names are part of the symbolic names, and must be included in addition to the brackets delimiting the bracket list.) Most metacharacters lose their special meaning inside lists. To include a literal ] place it first in the list. Similarly, to include a literal ^ place it anywhere but first. Finally, to include a literal - place it last.

The period . matches any single character. The symbol \w is a synonym for [[:alnum:]] and \W is a synonym for [^[:alnum]].

The caret ^ and the dollar sign $ are metacharacters that respectively match the empty string at the beginning and end of a line. The symbols \< and \> respectively match the empty string at the beginning and end of a word. The symbol \b matches the empty string at the edge of a word, and \B matches the empty string provided it's not at the edge of a word.

A regular expression may be followed by one of several repetition operators:

? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{n,m} The preceding item is matched at least n times, but not more than m times.

Two regular expressions may be concatenated; the resulting regular expression matches any string formed by concatenating two substrings that respectively match the concatenated subexpressions.

Two regular expressions may be joined by the infix operator |; the resulting regular expression matches any string matching either subexpression.

Repetition takes precedence over concatenation, which in turn takes precedence over alternation. A whole subexpression may be enclosed in parentheses to override these precedence rules.

The backreference \n, where n is a single digit, matches the substring previously matched by the nth parenthesized subexpression of the regular expression.

Related Links:

Related Topics: UserDocumentationCategory, VarSEARCH, FormattedSearch, QuerySearch

-- Contributors: PeterThoeny, TWiki:Main.JohnTalintyre

Revision 102013-03-10 - TWikiContributor

 

Regular Expressions

Introduction

Regular expressions (REs), unlike simple queries, allow you to search for text which matches a particular pattern.

REs are similar to (but more poweful than) the "wildcards" used in the command-line interfaces found in operating systems such as Unix and MS-DOS. REs are used by sophisticated search engines, as well as by many Unix-based languages and tools ( e.g., awk, grep, lex, perl, and sed ).

Examples

compan(y|ies) Search for company, companies
(peter|paul) Search for peter, paul
bug* Search for bug, bugg, buggg or simply bu (a star matches zero or more instances of the previous character)
bug.* Search for bug, bugs, bugfix (a dot-star matches zero or more instances of any character)
[Bb]ag Search for Bag, bag
b[aiueo]g Second letter is a vowel. Matches bag, bug, big
b.g Second letter is any letter. Matches also b&g
[a-zA-Z] Matches any one letter (but not a number or a symbol)
[^0-9a-zA-Z] Matches any symbol (but not a number or a letter)
[A-Z][A-Z]* Matches one or more uppercase letters
[0-9]{3}-[0-9]{2}-[0-9]{4} US social security number, e.g. 123-45-6789
Chart;PNG;!JPG Search for topics containing the words Chart and PNG and not JPG. The ";" and "!" are TWiki-specific operators and are not part of regular expression

Searches with "and" combinations

A TWiki type="regex" SEARCH introduces two special characters to regular expressions:

  • The semicolon ";" is an AND-operator.
    Example search for "form" and "template": form;template
  • The exclamation point "!" as a NOT-operator.
    Example search for "soap" and "wsdl" and not "shampoo": soap;wsdl;!shampoo

TWiki also supports a SQL-like query search where you can literally use AND and NOT operators.

Use Google if your TWiki site is public. Example search for "form" and "template" at TWiki.org: site:twiki.org +form +template

Advanced

Here is stuff for our UNIX freaks: (copied from 'man egrep')

A regular expression is a pattern that describes a set of strings. Regular expressions are constructed analogously to arithmetic expressions, by using various operators to combine smaller expressions.

The fundamental building blocks are the regular expressions that match a single character. Most characters, including all letters and digits, are regular expressions that match themselves. Any metacharacter with special meaning may be quoted by preceding it with a backslash.

A bracket expression is a list of characters enclosed by [ and ]. It matches any single character in that list; if the first character of the list is the caret ^ then it matches any character not in the list. For example, the regular expression [0123456789] matches any single digit.

Within a bracket expression, a range expression consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, inclusive, using the locale's collating sequence and character set. For example, in the default C locale, [a-d] is equivalent to [abcd]. Many locales sort characters in dictionary order, and in these locales [a-d] is typically not equivalent to [abcd]; it might be equivalent to [aBbCcDd], for example.

Finally, certain named classes of characters are predefined within bracket expressions, as follows. Their names are self explanatory, and they are [:alnum:], [:alpha:], [:cntrl:], [:digit:], [:graph:], [:lower:], [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:]. For example, [[:alnum:]] means [0-9A-Za-z], except the latter form depends upon the C locale and the ASCII character encoding, whereas the former is independent of locale and character set. (Note that the brackets in these class names are part of the symbolic names, and must be included in addition to the brackets delimiting the bracket list.) Most metacharacters lose their special meaning inside lists. To include a literal ] place it first in the list. Similarly, to include a literal ^ place it anywhere but first. Finally, to include a literal - place it last.

The period . matches any single character. The symbol \w is a synonym for [[:alnum:]] and \W is a synonym for [^[:alnum]].

The caret ^ and the dollar sign $ are metacharacters that respectively match the empty string at the beginning and end of a line. The symbols \< and \> respectively match the empty string at the beginning and end of a word. The symbol \b matches the empty string at the edge of a word, and \B matches the empty string provided it's not at the edge of a word.

A regular expression may be followed by one of several repetition operators:

? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{n,m} The preceding item is matched at least n times, but not more than m times.

Two regular expressions may be concatenated; the resulting regular expression matches any string formed by concatenating two substrings that respectively match the concatenated subexpressions.

Two regular expressions may be joined by the infix operator |; the resulting regular expression matches any string matching either subexpression.

Repetition takes precedence over concatenation, which in turn takes precedence over alternation. A whole subexpression may be enclosed in parentheses to override these precedence rules.

The backreference \n, where n is a single digit, matches the substring previously matched by the nth parenthesized subexpression of the regular expression.

Related Links:

Added:
>
>
 

Related Topics: UserDocumentationCategory, VarSEARCH, FormattedSearch, QuerySearch

Changed:
<
<
-- Contributors: PeterThoeny, JohnTalintyre
>
>
-- Contributors: PeterThoeny, TWiki:Main.JohnTalintyre
 

Revision 92010-05-03 - TWikiContributor

 

Regular Expressions

Added:
>
>
 

Introduction

Regular expressions (REs), unlike simple queries, allow you to search for text which matches a particular pattern.

REs are similar to (but more poweful than) the "wildcards" used in the command-line interfaces found in operating systems such as Unix and MS-DOS. REs are used by sophisticated search engines, as well as by many Unix-based languages and tools ( e.g., awk, grep, lex, perl, and sed ).

Examples

compan(y|ies) Search for company, companies
(peter|paul) Search for peter, paul
bug* Search for bug, bugg, buggg or simply bu (a star matches zero or more instances of the previous character)
bug.* Search for bug, bugs, bugfix (a dot-star matches zero or more instances of any character)
[Bb]ag Search for Bag, bag
b[aiueo]g Second letter is a vowel. Matches bag, bug, big
b.g Second letter is any letter. Matches also b&g
[a-zA-Z] Matches any one letter (but not a number or a symbol)
[^0-9a-zA-Z] Matches any symbol (but not a number or a letter)
[A-Z][A-Z]* Matches one or more uppercase letters
[0-9]{3}-[0-9]{2}-[0-9]{4} US social security number, e.g. 123-45-6789
Changed:
<
<
PNG;Chart Search for topics containing the words PNG and Chart. The ";" and separator is TWiki-specific and is not a regular expression; it is a useful facility that is enabled when regular expression searching is enabled.
>
>
Chart;PNG;!JPG Search for topics containing the words Chart and PNG and not JPG. The ";" and "!" are TWiki-specific operators and are not part of regular expression
 

Searches with "and" combinations

Changed:
<
<
  • TWiki extends the regular expressions with an and search. The delimiter is a semicolon ;. Example search for "form" and "template": form;template
>
>
A TWiki type="regex" SEARCH introduces two special characters to regular expressions:
 
Changed:
<
<
  • Use Google if your TWiki site is public. Example search for "form" and "template" at TWiki.org: site:twiki.org +form +template
>
>
  • The semicolon ";" is an AND-operator.
    Example search for "form" and "template": form;template
Added:
>
>
  • The exclamation point "!" as a NOT-operator.
    Example search for "soap" and "wsdl" and not "shampoo": soap;wsdl;!shampoo
 
Added:
>
>
TWiki also supports a SQL-like query search where you can literally use AND and NOT operators.

Use Google if your TWiki site is public. Example search for "form" and "template" at TWiki.org: site:twiki.org +form +template

 

Advanced

Here is stuff for our UNIX freaks: (copied from 'man egrep')

A regular expression is a pattern that describes a set of strings. Regular expressions are constructed analogously to arithmetic expressions, by using various operators to combine smaller expressions.

The fundamental building blocks are the regular expressions that match a single character. Most characters, including all letters and digits, are regular expressions that match themselves. Any metacharacter with special meaning may be quoted by preceding it with a backslash.

A bracket expression is a list of characters enclosed by [ and ]. It matches any single character in that list; if the first character of the list is the caret ^ then it matches any character not in the list. For example, the regular expression [0123456789] matches any single digit.

Within a bracket expression, a range expression consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, inclusive, using the locale's collating sequence and character set. For example, in the default C locale, [a-d] is equivalent to [abcd]. Many locales sort characters in dictionary order, and in these locales [a-d] is typically not equivalent to [abcd]; it might be equivalent to [aBbCcDd], for example.

Finally, certain named classes of characters are predefined within bracket expressions, as follows. Their names are self explanatory, and they are [:alnum:], [:alpha:], [:cntrl:], [:digit:], [:graph:], [:lower:], [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:]. For example, [[:alnum:]] means [0-9A-Za-z], except the latter form depends upon the C locale and the ASCII character encoding, whereas the former is independent of locale and character set. (Note that the brackets in these class names are part of the symbolic names, and must be included in addition to the brackets delimiting the bracket list.) Most metacharacters lose their special meaning inside lists. To include a literal ] place it first in the list. Similarly, to include a literal ^ place it anywhere but first. Finally, to include a literal - place it last.

The period . matches any single character. The symbol \w is a synonym for [[:alnum:]] and \W is a synonym for [^[:alnum]].

The caret ^ and the dollar sign $ are metacharacters that respectively match the empty string at the beginning and end of a line. The symbols \< and \> respectively match the empty string at the beginning and end of a word. The symbol \b matches the empty string at the edge of a word, and \B matches the empty string provided it's not at the edge of a word.

A regular expression may be followed by one of several repetition operators:

? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{n,m} The preceding item is matched at least n times, but not more than m times.

Two regular expressions may be concatenated; the resulting regular expression matches any string formed by concatenating two substrings that respectively match the concatenated subexpressions.

Two regular expressions may be joined by the infix operator |; the resulting regular expression matches any string matching either subexpression.

Repetition takes precedence over concatenation, which in turn takes precedence over alternation. A whole subexpression may be enclosed in parentheses to override these precedence rules.

The backreference \n, where n is a single digit, matches the substring previously matched by the nth parenthesized subexpression of the regular expression.

Related Links:

Changed:
<
<
Related Topics: UserDocumentationCategory
>
>
Related Topics: UserDocumentationCategory, VarSEARCH, FormattedSearch, QuerySearch
Added:
>
>
-- Contributors: PeterThoeny, JohnTalintyre
 

Revision 82006-11-22 - TWikiContributor

 

Regular Expressions

Introduction

Regular expressions (REs), unlike simple queries, allow you to search for text which matches a particular pattern.

REs are similar to (but more poweful than) the "wildcards" used in the command-line interfaces found in operating systems such as Unix and MS-DOS. REs are used by sophisticated search engines, as well as by many Unix-based languages and tools ( e.g., awk, grep, lex, perl, and sed ).

Examples

compan(y|ies) Search for company, companies
(peter|paul) Search for peter, paul
bug* Search for bug, bugg, buggg or simply bu (a star matches zero or more instances of the previous character)
bug.* Search for bug, bugs, bugfix (a dot-star matches zero or more instances of any character)
[Bb]ag Search for Bag, bag
b[aiueo]g Second letter is a vowel. Matches bag, bug, big
b.g Second letter is any letter. Matches also b&g
[a-zA-Z] Matches any one letter (but not a number or a symbol)
[^0-9a-zA-Z] Matches any symbol (but not a number or a letter)
[A-Z][A-Z]* Matches one or more uppercase letters
[0-9]{3}-[0-9]{2}-[0-9]{4} US social security number, e.g. 123-45-6789
PNG;Chart Search for topics containing the words PNG and Chart. The ";" and separator is TWiki-specific and is not a regular expression; it is a useful facility that is enabled when regular expression searching is enabled.

Searches with "and" combinations

  • TWiki extends the regular expressions with an and search. The delimiter is a semicolon ;. Example search for "form" and "template": form;template

  • Use Google if your TWiki site is public. Example search for "form" and "template" at TWiki.org: site:twiki.org +form +template

Advanced

Here is stuff for our UNIX freaks: (copied from 'man egrep')

A regular expression is a pattern that describes a set of strings. Regular expressions are constructed analogously to arithmetic expressions, by using various operators to combine smaller expressions.

The fundamental building blocks are the regular expressions that match a single character. Most characters, including all letters and digits, are regular expressions that match themselves. Any metacharacter with special meaning may be quoted by preceding it with a backslash.

A bracket expression is a list of characters enclosed by [ and ]. It matches any single character in that list; if the first character of the list is the caret ^ then it matches any character not in the list. For example, the regular expression [0123456789] matches any single digit.

Within a bracket expression, a range expression consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, inclusive, using the locale's collating sequence and character set. For example, in the default C locale, [a-d] is equivalent to [abcd]. Many locales sort characters in dictionary order, and in these locales [a-d] is typically not equivalent to [abcd]; it might be equivalent to [aBbCcDd], for example.

Finally, certain named classes of characters are predefined within bracket expressions, as follows. Their names are self explanatory, and they are [:alnum:], [:alpha:], [:cntrl:], [:digit:], [:graph:], [:lower:], [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:]. For example, [[:alnum:]] means [0-9A-Za-z], except the latter form depends upon the C locale and the ASCII character encoding, whereas the former is independent of locale and character set. (Note that the brackets in these class names are part of the symbolic names, and must be included in addition to the brackets delimiting the bracket list.) Most metacharacters lose their special meaning inside lists. To include a literal ] place it first in the list. Similarly, to include a literal ^ place it anywhere but first. Finally, to include a literal - place it last.

The period . matches any single character. The symbol \w is a synonym for [[:alnum:]] and \W is a synonym for [^[:alnum]].

The caret ^ and the dollar sign $ are metacharacters that respectively match the empty string at the beginning and end of a line. The symbols \< and \> respectively match the empty string at the beginning and end of a word. The symbol \b matches the empty string at the edge of a word, and \B matches the empty string provided it's not at the edge of a word.

A regular expression may be followed by one of several repetition operators:

? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{n,m} The preceding item is matched at least n times, but not more than m times.

Two regular expressions may be concatenated; the resulting regular expression matches any string formed by concatenating two substrings that respectively match the concatenated subexpressions.

Two regular expressions may be joined by the infix operator |; the resulting regular expression matches any string matching either subexpression.

Repetition takes precedence over concatenation, which in turn takes precedence over alternation. A whole subexpression may be enclosed in parentheses to override these precedence rules.

The backreference \n, where n is a single digit, matches the substring previously matched by the nth parenthesized subexpression of the regular expression.

Added:
>
>
Related Links:
  Related Topics: UserDocumentationCategory

Revision 72005-03-27 - TWikiContributor

 

Regular Expressions

Introduction

Regular expressions (REs), unlike simple queries, allow you to search for text which matches a particular pattern.

REs are similar to (but more poweful than) the "wildcards" used in the command-line interfaces found in operating systems such as Unix and MS-DOS. REs are used by sophisticated search engines, as well as by many Unix-based languages and tools ( e.g., awk, grep, lex, perl, and sed ).

Examples

compan(y|ies) Search for company, companies
(peter|paul) Search for peter, paul
bug* Search for bug, bugg, buggg or simply bu (a star matches zero or more instances of the previous character)
bug.* Search for bug, bugs, bugfix (a dot-star matches zero or more instances of any character)
[Bb]ag Search for Bag, bag
b[aiueo]g Second letter is a vowel. Matches bag, bug, big
b.g Second letter is any letter. Matches also b&g
[a-zA-Z] Matches any one letter (but not a number or a symbol)
[^0-9a-zA-Z] Matches any symbol (but not a number or a letter)
[A-Z][A-Z]* Matches one or more uppercase letters
[0-9]{3}-[0-9]{2}-[0-9]{4} US social security number, e.g. 123-45-6789
PNG;Chart Search for topics containing the words PNG and Chart. The ";" and separator is TWiki-specific and is not a regular expression; it is a useful facility that is enabled when regular expression searching is enabled.

Searches with "and" combinations

Changed:
<
<
  • TWiki extends the regular expressions with an and search. The delimiter is a semicolon ;. Example search for "form" and "template": form;template
>
>
  • TWiki extends the regular expressions with an and search. The delimiter is a semicolon ;. Example search for "form" and "template": form;template
 
Changed:
<
<
  • Use Google if your TWiki site is public. Example search for "form" and "template" at TWiki.org: site:twiki.org +form +template
>
>
  • Use Google if your TWiki site is public. Example search for "form" and "template" at TWiki.org: site:twiki.org +form +template
 

Advanced

Here is stuff for our UNIX freaks: (copied from 'man egrep')

A regular expression is a pattern that describes a set of strings. Regular expressions are constructed analogously to arithmetic expressions, by using various operators to combine smaller expressions.

The fundamental building blocks are the regular expressions that match a single character. Most characters, including all letters and digits, are regular expressions that match themselves. Any metacharacter with special meaning may be quoted by preceding it with a backslash.

A bracket expression is a list of characters enclosed by [ and ]. It matches any single character in that list; if the first character of the list is the caret ^ then it matches any character not in the list. For example, the regular expression [0123456789] matches any single digit.

Within a bracket expression, a range expression consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, inclusive, using the locale's collating sequence and character set. For example, in the default C locale, [a-d] is equivalent to [abcd]. Many locales sort characters in dictionary order, and in these locales [a-d] is typically not equivalent to [abcd]; it might be equivalent to [aBbCcDd], for example.

Finally, certain named classes of characters are predefined within bracket expressions, as follows. Their names are self explanatory, and they are [:alnum:], [:alpha:], [:cntrl:], [:digit:], [:graph:], [:lower:], [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:]. For example, [[:alnum:]] means [0-9A-Za-z], except the latter form depends upon the C locale and the ASCII character encoding, whereas the former is independent of locale and character set. (Note that the brackets in these class names are part of the symbolic names, and must be included in addition to the brackets delimiting the bracket list.) Most metacharacters lose their special meaning inside lists. To include a literal ] place it first in the list. Similarly, to include a literal ^ place it anywhere but first. Finally, to include a literal - place it last.

The period . matches any single character. The symbol \w is a synonym for [[:alnum:]] and \W is a synonym for [^[:alnum]].

The caret ^ and the dollar sign $ are metacharacters that respectively match the empty string at the beginning and end of a line. The symbols \< and \> respectively match the empty string at the beginning and end of a word. The symbol \b matches the empty string at the edge of a word, and \B matches the empty string provided it's not at the edge of a word.

A regular expression may be followed by one of several repetition operators:

? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{n,m} The preceding item is matched at least n times, but not more than m times.

Two regular expressions may be concatenated; the resulting regular expression matches any string formed by concatenating two substrings that respectively match the concatenated subexpressions.

Two regular expressions may be joined by the infix operator |; the resulting regular expression matches any string matching either subexpression.

Repetition takes precedence over concatenation, which in turn takes precedence over alternation. A whole subexpression may be enclosed in parentheses to override these precedence rules.

The backreference \n, where n is a single digit, matches the substring previously matched by the nth parenthesized subexpression of the regular expression.

Related Topics: UserDocumentationCategory

Revision 62005-03-27 - TWikiContributor

Changed:
<
<

Regular Expressions

Introduction

Regular expressions (REs), unlike simple queries, allow you to search for text which matches a particular pattern.

REs are similar to (but more poweful than) the "wildcards" used in the command-line interfaces found in operating systems such as Unix and MS-DOS. REs are used by sophisticated search engines, as well as by many Unix-based languages and tools ( e.g., awk, grep, lex, perl, and sed ).

Examples

compan(y|ies) Search for company, companies
(peter|paul) Search for peter, paul
bug* Search for bug, bugg, buggg or simply bu (a star matches zero or more instances of the previous character)
bug.* Search for bug, bugs, bugfix (a dot-star matches zero or more instances of any character)
[Bb]ag Search for Bag, bag
b[aiueo]g Second letter is a vowel. Matches bag, bug, big
b.g Second letter is any letter. Matches also b&g
[a-zA-Z] Matches any one letter (but not a number or a symbol)
[^0-9a-zA-Z] Matches any symbol (but not a number or a letter)
[A-Z][A-Z]* Matches one or more uppercase letters
[0-9]{3}-[0-9]{2}-[0-9]{4} US social security number, e.g. 123-45-6789
PNG;Chart Search for topics containing the words PNG and Chart. The ";" and separator is TWiki-specific and is not a regular expression; it is a useful facility that is enabled when regular expression searching is enabled.

Searches with "and" combinations

  • TWiki extends the regular expressions with an and search. The delimiter is a semicolon ;. Example search for "form" and "template": form;template

  • Use Google if your TWiki site is public. Example search for "form" and "template" at TWiki.org: site:twiki.org +form +template

Advanced

Here is stuff for our UNIX freaks: (copied from 'man egrep')

A regular expression is a pattern that describes a set of strings. Regular expressions are constructed analogously to arithmetic expressions, by using various operators to combine smaller expressions.

The fundamental building blocks are the regular expressions that match a single character. Most characters, including all letters and digits, are regular expressions that match themselves. Any metacharacter with special meaning may be quoted by preceding it with a backslash.

A bracket expression is a list of characters enclosed by [ and ]. It matches any single character in that list; if the first character of the list is the caret ^ then it matches any character not in the list. For example, the regular expression [0123456789] matches any single digit.

Within a bracket expression, a range expression consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, inclusive, using the locale's collating sequence and character set. For example, in the default C locale, [a-d] is equivalent to [abcd]. Many locales sort characters in dictionary order, and in these locales [a-d] is typically not equivalent to [abcd]; it might be equivalent to [aBbCcDd], for example.

Finally, certain named classes of characters are predefined within bracket expressions, as follows. Their names are self explanatory, and they are [:alnum:], [:alpha:], [:cntrl:], [:digit:], [:graph:], [:lower:], [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:]. For example, [[:alnum:]] means [0-9A-Za-z], except the latter form depends upon the C locale and the ASCII character encoding, whereas the former is independent of locale and character set. (Note that the brackets in these class names are part of the symbolic names, and must be included in addition to the brackets delimiting the bracket list.) Most metacharacters lose their special meaning inside lists. To include a literal ] place it first in the list. Similarly, to include a literal ^ place it anywhere but first. Finally, to include a literal - place it last.

The period . matches any single character. The symbol \w is a synonym for [[:alnum:]] and \W is a synonym for [^[:alnum]].

The caret ^ and the dollar sign $ are metacharacters that respectively match the empty string at the beginning and end of a line. The symbols \< and \> respectively match the empty string at the beginning and end of a word. The symbol \b matches the empty string at the edge of a word, and \B matches the empty string provided it's not at the edge of a word.

A regular expression may be followed by one of several repetition operators:

? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{n,m} The preceding item is matched at least n times, but not more than m times.

Two regular expressions may be concatenated; the resulting regular expression matches any string formed by concatenating two substrings that respectively match the concatenated subexpressions.

Two regular expressions may be joined by the infix operator |; the resulting regular expression matches any string matching either subexpression.

Repetition takes precedence over concatenation, which in turn takes precedence over alternation. A whole subexpression may be enclosed in parentheses to override these precedence rules.

The backreference \n, where n is a single digit, matches the substring previously matched by the nth parenthesized subexpression of the regular expression.

>
>

Regular Expressions

Introduction

Regular expressions (REs), unlike simple queries, allow you to search for text which matches a particular pattern.

REs are similar to (but more poweful than) the "wildcards" used in the command-line interfaces found in operating systems such as Unix and MS-DOS. REs are used by sophisticated search engines, as well as by many Unix-based languages and tools ( e.g., awk, grep, lex, perl, and sed ).

Examples

compan(y|ies) Search for company, companies
(peter|paul) Search for peter, paul
bug* Search for bug, bugg, buggg or simply bu (a star matches zero or more instances of the previous character)
bug.* Search for bug, bugs, bugfix (a dot-star matches zero or more instances of any character)
[Bb]ag Search for Bag, bag
b[aiueo]g Second letter is a vowel. Matches bag, bug, big
b.g Second letter is any letter. Matches also b&g
[a-zA-Z] Matches any one letter (but not a number or a symbol)
[^0-9a-zA-Z] Matches any symbol (but not a number or a letter)
[A-Z][A-Z]* Matches one or more uppercase letters
[0-9]{3}-[0-9]{2}-[0-9]{4} US social security number, e.g. 123-45-6789
PNG;Chart Search for topics containing the words PNG and Chart. The ";" and separator is TWiki-specific and is not a regular expression; it is a useful facility that is enabled when regular expression searching is enabled.

Searches with "and" combinations

  • TWiki extends the regular expressions with an and search. The delimiter is a semicolon ;. Example search for "form" and "template": form;template

  • Use Google if your TWiki site is public. Example search for "form" and "template" at TWiki.org: site:twiki.org +form +template

Advanced

Here is stuff for our UNIX freaks: (copied from 'man egrep')

A regular expression is a pattern that describes a set of strings. Regular expressions are constructed analogously to arithmetic expressions, by using various operators to combine smaller expressions.

The fundamental building blocks are the regular expressions that match a single character. Most characters, including all letters and digits, are regular expressions that match themselves. Any metacharacter with special meaning may be quoted by preceding it with a backslash.

A bracket expression is a list of characters enclosed by [ and ]. It matches any single character in that list; if the first character of the list is the caret ^ then it matches any character not in the list. For example, the regular expression [0123456789] matches any single digit.

Within a bracket expression, a range expression consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, inclusive, using the locale's collating sequence and character set. For example, in the default C locale, [a-d] is equivalent to [abcd]. Many locales sort characters in dictionary order, and in these locales [a-d] is typically not equivalent to [abcd]; it might be equivalent to [aBbCcDd], for example.

Finally, certain named classes of characters are predefined within bracket expressions, as follows. Their names are self explanatory, and they are [:alnum:], [:alpha:], [:cntrl:], [:digit:], [:graph:], [:lower:], [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:]. For example, [[:alnum:]] means [0-9A-Za-z], except the latter form depends upon the C locale and the ASCII character encoding, whereas the former is independent of locale and character set. (Note that the brackets in these class names are part of the symbolic names, and must be included in addition to the brackets delimiting the bracket list.) Most metacharacters lose their special meaning inside lists. To include a literal ] place it first in the list. Similarly, to include a literal ^ place it anywhere but first. Finally, to include a literal - place it last.

The period . matches any single character. The symbol \w is a synonym for [[:alnum:]] and \W is a synonym for [^[:alnum]].

The caret ^ and the dollar sign $ are metacharacters that respectively match the empty string at the beginning and end of a line. The symbols \< and \> respectively match the empty string at the beginning and end of a word. The symbol \b matches the empty string at the edge of a word, and \B matches the empty string provided it's not at the edge of a word.

A regular expression may be followed by one of several repetition operators:

? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{n,m} The preceding item is matched at least n times, but not more than m times.

Two regular expressions may be concatenated; the resulting regular expression matches any string formed by concatenating two substrings that respectively match the concatenated subexpressions.

Two regular expressions may be joined by the infix operator |; the resulting regular expression matches any string matching either subexpression.

Repetition takes precedence over concatenation, which in turn takes precedence over alternation. A whole subexpression may be enclosed in parentheses to override these precedence rules.

The backreference \n, where n is a single digit, matches the substring previously matched by the nth parenthesized subexpression of the regular expression.

Added:
>
>
Related Topics: UserDocumentationCategory
 

Revision 52003-04-15 - PeterThoeny

 

Regular Expressions

Introduction

Regular expressions (REs), unlike simple queries, allow you to search for text which matches a particular pattern.

REs are similar to (but more poweful than) the "wildcards" used in the command-line interfaces found in operating systems such as Unix and MS-DOS. REs are used by sophisticated search engines, as well as by many Unix-based languages and tools ( e.g., awk, grep, lex, perl, and sed ).

Examples

compan(y|ies) Search for company, companies
(peter|paul) Search for peter, paul
Changed:
<
<
bug* Search for bug, bugs, bugfix
>
>
bug* Search for bug, bugg, buggg or simply bu (a star matches zero or more instances of the previous character)
Added:
>
>
bug.* Search for bug, bugs, bugfix (a dot-star matches zero or more instances of any character)
 
[Bb]ag Search for Bag, bag
b[aiueo]g Second letter is a vowel. Matches bag, bug, big
b.g Second letter is any letter. Matches also b&g
[a-zA-Z] Matches any one letter (but not a number or a symbol)
[^0-9a-zA-Z] Matches any symbol (but not a number or a letter)
[A-Z][A-Z]* Matches one or more uppercase letters
[0-9]{3}-[0-9]{2}-[0-9]{4} US social security number, e.g. 123-45-6789
PNG;Chart Search for topics containing the words PNG and Chart. The ";" and separator is TWiki-specific and is not a regular expression; it is a useful facility that is enabled when regular expression searching is enabled.

Searches with "and" combinations

  • TWiki extends the regular expressions with an and search. The delimiter is a semicolon ;. Example search for "form" and "template": form;template

  • Use Google if your TWiki site is public. Example search for "form" and "template" at TWiki.org: site:twiki.org +form +template

Advanced

Here is stuff for our UNIX freaks: (copied from 'man egrep')

A regular expression is a pattern that describes a set of strings. Regular expressions are constructed analogously to arithmetic expressions, by using various operators to combine smaller expressions.

The fundamental building blocks are the regular expressions that match a single character. Most characters, including all letters and digits, are regular expressions that match themselves. Any metacharacter with special meaning may be quoted by preceding it with a backslash.

A bracket expression is a list of characters enclosed by [ and ]. It matches any single character in that list; if the first character of the list is the caret ^ then it matches any character not in the list. For example, the regular expression [0123456789] matches any single digit.

Within a bracket expression, a range expression consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, inclusive, using the locale's collating sequence and character set. For example, in the default C locale, [a-d] is equivalent to [abcd]. Many locales sort characters in dictionary order, and in these locales [a-d] is typically not equivalent to [abcd]; it might be equivalent to [aBbCcDd], for example.

Finally, certain named classes of characters are predefined within bracket expressions, as follows. Their names are self explanatory, and they are [:alnum:], [:alpha:], [:cntrl:], [:digit:], [:graph:], [:lower:], [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:]. For example, [[:alnum:]] means [0-9A-Za-z], except the latter form depends upon the C locale and the ASCII character encoding, whereas the former is independent of locale and character set. (Note that the brackets in these class names are part of the symbolic names, and must be included in addition to the brackets delimiting the bracket list.) Most metacharacters lose their special meaning inside lists. To include a literal ] place it first in the list. Similarly, to include a literal ^ place it anywhere but first. Finally, to include a literal - place it last.

The period . matches any single character. The symbol \w is a synonym for [[:alnum:]] and \W is a synonym for [^[:alnum]].

The caret ^ and the dollar sign $ are metacharacters that respectively match the empty string at the beginning and end of a line. The symbols \< and \> respectively match the empty string at the beginning and end of a word. The symbol \b matches the empty string at the edge of a word, and \B matches the empty string provided it's not at the edge of a word.

A regular expression may be followed by one of several repetition operators:

? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{n,m} The preceding item is matched at least n times, but not more than m times.

Two regular expressions may be concatenated; the resulting regular expression matches any string formed by concatenating two substrings that respectively match the concatenated subexpressions.

Two regular expressions may be joined by the infix operator |; the resulting regular expression matches any string matching either subexpression.

Repetition takes precedence over concatenation, which in turn takes precedence over alternation. A whole subexpression may be enclosed in parentheses to override these precedence rules.

The backreference \n, where n is a single digit, matches the substring previously matched by the nth parenthesized subexpression of the regular expression.

Revision 42003-03-22 - PeterThoeny

 

Regular Expressions

Deleted:
<
<
 

Introduction

Changed:
<
<
Regular expressions (REs), unlike simple queries, allow you to search for text which matches a particular pattern.
>
>
Regular expressions (REs), unlike simple queries, allow you to search for text which matches a particular pattern.
  REs are similar to (but more poweful than) the "wildcards" used in the command-line interfaces found in operating systems such as Unix and MS-DOS. REs are used by sophisticated search engines, as well as by many Unix-based languages and tools ( e.g., awk, grep, lex, perl, and sed ).

Examples

compan(y|ies) Search for company, companies
(peter|paul) Search for peter, paul
bug* Search for bug, bugs, bugfix
[Bb]ag Search for Bag, bag
b[aiueo]g Second letter is a vowel. Matches bag, bug, big
b.g Second letter is any letter. Matches also b&g
[a-zA-Z] Matches any one letter (but not a number or a symbol)
[^0-9a-zA-Z] Matches any symbol (but not a number or a letter)
[A-Z][A-Z]* Matches one or more uppercase letters
[0-9]{3}-[0-9]{2}-[0-9]{4} US social security number, e.g. 123-45-6789
Changed:
<
<
PNG;Chart Search for topics containing the words PNG and Chart. This is not a regular expression! But a useful facility that is enabled when regular expression searching is enabled.
>
>
PNG;Chart Search for topics containing the words PNG and Chart. The ";" and separator is TWiki-specific and is not a regular expression; it is a useful facility that is enabled when regular expression searching is enabled.
 

Searches with "and" combinations

  • TWiki extends the regular expressions with an and search. The delimiter is a semicolon ;. Example search for "form" and "template": form;template

  • Use Google if your TWiki site is public. Example search for "form" and "template" at TWiki.org: site:twiki.org +form +template

Advanced

Here is stuff for our UNIX freaks: (copied from 'man egrep')

A regular expression is a pattern that describes a set of strings. Regular expressions are constructed analogously to arithmetic expressions, by using various operators to combine smaller expressions.

The fundamental building blocks are the regular expressions that match a single character. Most characters, including all letters and digits, are regular expressions that match themselves. Any metacharacter with special meaning may be quoted by preceding it with a backslash.

A bracket expression is a list of characters enclosed by [ and ]. It matches any single character in that list; if the first character of the list is the caret ^ then it matches any character not in the list. For example, the regular expression [0123456789] matches any single digit.

Changed:
<
<
Within a bracket expression, a range expression consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, inclusive, using the locale's collating sequence and character set. For example, in the default C locale, [a-d] is equivalent to [abcd]. Many locales sort characters in dictionary order, and in these locales [a-d] is typically not equivalent to [abcd]; it might be equivalent to [aBbCcDd], for example.
>
>
Within a bracket expression, a range expression consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, inclusive, using the locale's collating sequence and character set. For example, in the default C locale, [a-d] is equivalent to [abcd]. Many locales sort characters in dictionary order, and in these locales [a-d] is typically not equivalent to [abcd]; it might be equivalent to [aBbCcDd], for example.
  Finally, certain named classes of characters are predefined within bracket expressions, as follows. Their names are self explanatory, and they are [:alnum:], [:alpha:], [:cntrl:], [:digit:], [:graph:], [:lower:], [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:]. For example, [[:alnum:]] means [0-9A-Za-z], except the latter form depends upon the C locale and the ASCII character encoding, whereas the former is independent of locale and character set. (Note that the brackets in these class names are part of the symbolic names, and must be included in addition to the brackets delimiting the bracket list.) Most metacharacters lose their special meaning inside lists. To include a literal ] place it first in the list. Similarly, to include a literal ^ place it anywhere but first. Finally, to include a literal - place it last.

The period . matches any single character. The symbol \w is a synonym for [[:alnum:]] and \W is a synonym for [^[:alnum]].

The caret ^ and the dollar sign $ are metacharacters that respectively match the empty string at the beginning and end of a line. The symbols \< and \> respectively match the empty string at the beginning and end of a word. The symbol \b matches the empty string at the edge of a word, and \B matches the empty string provided it's not at the edge of a word.

A regular expression may be followed by one of several repetition operators:

? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{n,m} The preceding item is matched at least n times, but not more than m times.

Two regular expressions may be concatenated; the resulting regular expression matches any string formed by concatenating two substrings that respectively match the concatenated subexpressions.

Two regular expressions may be joined by the infix operator |; the resulting regular expression matches any string matching either subexpression.

Repetition takes precedence over concatenation, which in turn takes precedence over alternation. A whole subexpression may be enclosed in parentheses to override these precedence rules.

The backreference \n, where n is a single digit, matches the substring previously matched by the nth parenthesized subexpression of the regular expression.

Revision 32002-11-23 - PeterThoeny

Added:
>
>

Regular Expressions

Introduction

 Regular expressions (REs), unlike simple queries, allow you to search for text which matches a particular pattern.

REs are similar to (but more poweful than) the "wildcards" used in the command-line interfaces found in operating systems such as Unix and MS-DOS. REs are used by sophisticated search engines, as well as by many Unix-based languages and tools ( e.g., awk, grep, lex, perl, and sed ).

Changed:
<
<
Examples
>
>

Examples

 
Changed:
<
<
compan(y|ies) Search for company , companies
(peter|paul)
>
>
compan(y|ies) Search for company, companies
(peter|paul) Search for peter, paul
bug* Search for bug, bugs, bugfix
[Bb]ag Search for Bag, bag
b[aiueo]g Second letter is a vowel. Matches bag, bug, big
b.g Second letter is any letter. Matches also b&g
[a-zA-Z] Matches any one letter (but not a number or a symbol)
[^0-9a-zA-Z] Matches any symbol (but not a number or a letter)
[A-Z][A-Z]* Matches one or more uppercase letters
[0-9]{3}-[0-9]{2}-[0-9]{4} US social security number, e.g. 123-45-6789
PNG;Chart Search for topics containing the words PNG and Chart. This is not a regular expression! But a useful facility that is enabled when regular expression searching is enabled.
Deleted:
<
<
Search for peter , paul
bug* Search for bug , bugs , bugfix
[Bb]ag Search for Bag , bag
b[aiueo]g Second letter is a vowel. Matches bag , bug , big
b.g Second letter is any letter. Matches also b&g
[a-zA-Z] Matches any one letter (not a number and a symbol)
[^0-9a-zA-Z] Matches any symbol (not a number or a letter)
[A-Z][A-Z]* Matches one or more uppercase letters
[0-9][0-9][0-9]-[0-9][0-9]-
[0-9][0-9][0-9][0-9]
US social security number, e.g. 123-45-6789
 
Changed:
<
<
Here is stuff for our UNIX freaks:
>
>

Searches with "and" combinations

Deleted:
<
<
(copied from 'man grep')
 
Changed:
<
<

>
>
  • TWiki extends the regular expressions with an and search. The delimiter is a semicolon ;. Example search for "form" and "template": form;template
Deleted:
<
<
\c A backslash (\) followed by any special character is a one-character regular expression that matches the spe- cial character itself. The special characters are:
 
Changed:
<
<
+ `.', `*', `[', and `\' (period, asterisk,
>
>
  • Use Google if your TWiki site is public. Example search for "form" and "template" at TWiki.org: site:twiki.org +form +template
Deleted:
<
<
left square bracket, and backslash, respec- tively), which are always special, except when they appear within square brackets ([]).
 
Changed:
<
<
+ `^' (caret or circumflex), which is special
>
>

Advanced

Deleted:
<
<
at the beginning of an entire regular expres- sion, or when it immediately follows the left of a pair of square brackets ([]).
 
Changed:
<
<
+ $ (currency symbol), which is special at the
>
>
Here is stuff for our UNIX freaks: (copied from 'man egrep')
Deleted:
<
<
end of an entire regular expression.
 
Changed:
<
<
. A `.' (period) is a one-character regular expression that matches any character except NEWLINE.
>
>
A regular expression is a pattern that describes a set of strings. Regular expressions are constructed analogously to arithmetic expressions, by using various operators to combine smaller expressions.
Deleted:
<
<
[string] A non-empty string of characters enclosed in square brackets is a one-character regular expression that matches any one character in that string. If, however, the first character of the string is a `^' (a circum- flex or caret), the one-character regular expression matches any character except NEWLINE and the remaining characters in the string. The `^' has this special meaning only if it occurs first in the string. The `-' (minus) may be used to indicate a range of consecutive ASCII characters; for example, [0-9] is equivalent to [0123456789]. The `-' loses this special meaning if it occurs first (after an initial `^', if any) or last in the string. The `]' (right square bracket) does not terminate such a string when it is the first character within it (after an initial `^', if any); that is, []a-f] matches either `]' (a right square bracket ) or one of the letters a through f inclusive. The four characters `.', `*', `[', and `\' stand for themselves within such a string of characters.
 
Changed:
<
<
The following rules may be used to construct regular expres-
>
>
The fundamental building blocks are the regular expressions that match a single character. Most characters, including all letters and digits, are regular expressions that match themselves. Any metacharacter with special meaning may be quoted by preceding it with a backslash.
Deleted:
<
<
sions:
 
Changed:
<
<
* A one-character regular expression followed by `*' (an
>
>
A bracket expression is a list of characters enclosed by [ and ]. It matches any single character in that list; if the first character of the list is the caret ^ then it matches any character not in the list. For example, the regular expression [0123456789] matches any single digit.
Deleted:
<
<
asterisk) is a regular expression that matches zero or more occurrences of the one-character regular expres- sion. If there is any choice, the longest leftmost string that permits a match is chosen.
 
Changed:
<
<
^ A circumflex or caret (^) at the beginning of an entire
>
>
Within a bracket expression, a range expression consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, inclusive, using the locale's collating sequence and character set. For example, in the default C locale, [a-d] is equivalent to [abcd]. Many locales sort characters in dictionary order, and in these locales [a-d] is typically not equivalent to [abcd]; it might be equivalent to [aBbCcDd], for example.
Deleted:
<
<
regular expression constrains that regular expression to match an initial segment of a line.
 
Changed:
<
<
$ A currency symbol ($) at the end of an entire regular
>
>
Finally, certain named classes of characters are predefined within bracket expressions, as follows. Their names are self explanatory, and they are [:alnum:], [:alpha:], [:cntrl:], [:digit:], [:graph:], [:lower:], [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:]. For example, [[:alnum:]] means [0-9A-Za-z], except the latter form depends upon the C locale and the ASCII character encoding, whereas the former is independent of locale and character set. (Note that the brackets in these class names are part of the symbolic names, and must be included in addition to the brackets delimiting the bracket list.) Most metacharacters lose their special meaning inside lists. To include a literal ] place it first in the list. Similarly, to include a literal ^ place it anywhere but first. Finally, to include a literal - place it last.
Deleted:
<
<
expression constrains that regular expression to match a final segment of a line.
 
Changed:
<
<
* A regular expression (not just a one-
>
>
The period . matches any single character. The symbol \w is a synonym for [[:alnum:]] and \W is a synonym for [^[:alnum]].
Deleted:
<
<
character regular expression) followed by `*' (an asterisk) is a regular expression that matches zero or more occurrences of the one- character regular expression. If there is any choice, the longest leftmost string that permits a match is chosen.
 
Changed:
<
<
+ A regular expression followed by `+' (a plus
>
>
The caret ^ and the dollar sign $ are metacharacters that respectively match the empty string at the beginning and end of a line. The symbols \< and \> respectively match the empty string at the beginning and end of a word. The symbol \b matches the empty string at the edge of a word, and \B matches the empty string provided it's not at the edge of a word.
Deleted:
<
<
sign) is a regular expression that matches one or more occurrences of the one-character regular expression. If there is any choice, the longest leftmost string that permits a match is chosen.
 
Changed:
<
<
? A regular expression followed by `?' (a ques- tion mark) is a regular expression that matches zero or one occurrences of the one- character regular expression. If there is any choice, the longest leftmost string that permits a match is chosen.
>
>
A regular expression may be followed by one of several repetition operators:
? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
Added:
>
>
{n,m} The preceding item is matched at least n times, but not more than m times.
 
Changed:
<
<
| Alternation: two regular expressions
>
>
Two regular expressions may be concatenated; the resulting regular expression matches any string formed by concatenating two substrings that respectively match the concatenated subexpressions.
Deleted:
<
<
separated by `|' or NEWLINE match either a match for the first or a match for the second.
 
Changed:
<
<
() A regular expression enclosed in parentheses
>
>
Two regular expressions may be joined by the infix operator |; the resulting regular expression matches any string matching either subexpression.
Deleted:
<
<
matches a match for the regular expression.
 
Changed:
<
<
The order of precedence of operators at the same parenthesis
>
>
Repetition takes precedence over concatenation, which in turn takes precedence over alternation. A whole subexpression may be enclosed in parentheses to override these precedence rules.
Deleted:
<
<
level is `[ ]' (character classes), then `*' `+' `?' (closures),then concatenation, then `|' (alternation)and NEWLINE.
 
Added:
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The backreference \n, where n is a single digit, matches the substring previously matched by the nth parenthesized subexpression of the regular expression.
 

Revision 22000-08-23 - PeterThoeny

Changed:
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Regular expressions allow more specific queries then a simple query.
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Regular expressions (REs), unlike simple queries, allow you to search for text which matches a particular pattern.
Added:
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REs are similar to (but more poweful than) the "wildcards" used in the command-line interfaces found in operating systems such as Unix and MS-DOS. REs are used by sophisticated search engines, as well as by many Unix-based languages and tools ( e.g., awk, grep, lex, perl, and sed ).
  Examples

compan(y|ies) Search for company , companies
(peter|paul) Search for peter , paul
bug* Search for bug , bugs , bugfix
[Bb]ag Search for Bag , bag
b[aiueo]g Second letter is a vowel. Matches bag , bug , big
b.g Second letter is any letter. Matches also b&g
[a-zA-Z] Matches any one letter (not a number and a symbol)
[^0-9a-zA-Z] Matches any symbol (not a number or a letter)
[A-Z][A-Z]* Matches one or more uppercase letters
[0-9][0-9][0-9]-[0-9][0-9]-
[0-9][0-9][0-9][0-9]
US social security number, e.g. 123-45-6789

Here is stuff for our UNIX freaks:
(copied from 'man grep')

	  \c	A backslash (\) followed by any special character is  a
			 one-character  regular expression that matches the spe-
			 cial character itself.  The special characters are:

					+	 `.', `*', `[',  and  `\'  (period,  asterisk,
						  left  square  bracket, and backslash, respec-
						  tively), which  are  always  special,  except
						  when they appear within square brackets ([]).

					+	 `^' (caret or circumflex), which  is  special
						  at the beginning of an entire regular expres-
						  sion, or when it immediately follows the left
						  of a pair of square brackets ([]).

					+	 $ (currency symbol), which is special at  the
						  end of an entire regular expression.							  

	  .	 A `.' (period) is a  one-character  regular  expression
			 that matches any character except NEWLINE.
 
	  [string]
			 A non-empty string of  characters  enclosed  in  square
			 brackets  is  a  one-character  regular expression that
			 matches any one character in that string.  If, however,
			 the  first  character of the string is a `^' (a circum-
			 flex or caret), the  one-character  regular  expression
			 matches  any character except NEWLINE and the remaining
			 characters in the string.  The  `^'  has  this  special
			 meaning only if it occurs first in the string.  The `-'
			 (minus) may be used to indicate a range of  consecutive
			 ASCII  characters;  for example, [0-9] is equivalent to
			 [0123456789].  The `-' loses this special meaning if it
			 occurs  first (after an initial `^', if any) or last in
			 the string.  The `]' (right square  bracket)  does  not
			 terminate  such a string when it is the first character
			 within it (after an initial  `^',  if  any);  that  is,
			 []a-f]  matches either `]' (a right square bracket ) or
			 one of the letters a through  f  inclusive.	The  four
			 characters  `.', `*', `[', and `\' stand for themselves
			 within such a string of characters.

	  The following rules may be used to construct regular expres-
	  sions:

	  *	 A one-character regular expression followed by `*'  (an
			 asterisk)  is a regular expression that matches zero or
			 more occurrences of the one-character  regular  expres-
			 sion.	If  there  is  any choice, the longest leftmost
			 string that permits a match is chosen.

	  ^	 A circumflex or caret (^) at the beginning of an entire
			 regular  expression  constrains that regular expression
			 to match an initial segment of a line.

	  $	 A currency symbol ($) at the end of an  entire  regular
			 expression  constrains that regular expression to match
			 a final segment of a line.

	  *	 A  regular  expression  (not  just	a	one-
			 character regular expression) followed by `*'
			 (an asterisk) is a  regular  expression  that
			 matches  zero or more occurrences of the one-
			 character regular expression.	If  there  is
			 any  choice, the longest leftmost string that
			 permits a match is chosen.

	  +	 A regular expression followed by `+' (a  plus
			 sign)  is  a  regular expression that matches
			 one or more occurrences of the  one-character
			 regular  expression.  If there is any choice,
			 the longest leftmost string  that  permits  a
			 match is chosen.

	  ?	 A regular expression followed by `?' (a ques-
			 tion  mark)  is  a  regular  expression  that
			 matches zero or one occurrences of  the  one-
			 character  regular  expression.	If there is
			 any choice, the longest leftmost string  that
			 permits a match is chosen.

	  |	 Alternation:	 two	 regular	 expressions
			 separated  by  `|'  or NEWLINE match either a
			 match for  the  first  or  a  match  for  the
			 second.

	  ()	A regular expression enclosed in  parentheses
			 matches a match for the regular expression.

	  The order of precedence of operators at the same parenthesis
	  level  is  `[ ]'  (character  classes),  then  `*'  `+'  `?'
	  (closures),then  concatenation,  then  `|'  (alternation)and
	  NEWLINE.

Revision 12000-08-18 - PeterThoeny

 Regular expressions allow more specific queries then a simple query.

Examples

compan(y|ies) Search for company , companies
(peter|paul) Search for peter , paul
bug* Search for bug , bugs , bugfix
[Bb]ag Search for Bag , bag
b[aiueo]g Second letter is a vowel. Matches bag , bug , big
b.g Second letter is any letter. Matches also b&g
[a-zA-Z] Matches any one letter (not a number and a symbol)
[^0-9a-zA-Z] Matches any symbol (not a number or a letter)
[A-Z][A-Z]* Matches one or more uppercase letters
[0-9][0-9][0-9]-[0-9][0-9]-
[0-9][0-9][0-9][0-9]
US social security number, e.g. 123-45-6789

Here is stuff for our UNIX freaks:
(copied from 'man grep')

	  \c	A backslash (\) followed by any special character is  a
			 one-character  regular expression that matches the spe-
			 cial character itself.  The special characters are:

					+	 `.', `*', `[',  and  `\'  (period,  asterisk,
						  left  square  bracket, and backslash, respec-
						  tively), which  are  always  special,  except
						  when they appear within square brackets ([]).

					+	 `^' (caret or circumflex), which  is  special
						  at the beginning of an entire regular expres-
						  sion, or when it immediately follows the left
						  of a pair of square brackets ([]).

					+	 $ (currency symbol), which is special at  the
						  end of an entire regular expression.							  

	  .	 A `.' (period) is a  one-character  regular  expression
			 that matches any character except NEWLINE.
 
	  [string]
			 A non-empty string of  characters  enclosed  in  square
			 brackets  is  a  one-character  regular expression that
			 matches any one character in that string.  If, however,
			 the  first  character of the string is a `^' (a circum-
			 flex or caret), the  one-character  regular  expression
			 matches  any character except NEWLINE and the remaining
			 characters in the string.  The  `^'  has  this  special
			 meaning only if it occurs first in the string.  The `-'
			 (minus) may be used to indicate a range of  consecutive
			 ASCII  characters;  for example, [0-9] is equivalent to
			 [0123456789].  The `-' loses this special meaning if it
			 occurs  first (after an initial `^', if any) or last in
			 the string.  The `]' (right square  bracket)  does  not
			 terminate  such a string when it is the first character
			 within it (after an initial  `^',  if  any);  that  is,
			 []a-f]  matches either `]' (a right square bracket ) or
			 one of the letters a through  f  inclusive.	The  four
			 characters  `.', `*', `[', and `\' stand for themselves
			 within such a string of characters.

	  The following rules may be used to construct regular expres-
	  sions:

	  *	 A one-character regular expression followed by `*'  (an
			 asterisk)  is a regular expression that matches zero or
			 more occurrences of the one-character  regular  expres-
			 sion.	If  there  is  any choice, the longest leftmost
			 string that permits a match is chosen.

	  ^	 A circumflex or caret (^) at the beginning of an entire
			 regular  expression  constrains that regular expression
			 to match an initial segment of a line.

	  $	 A currency symbol ($) at the end of an  entire  regular
			 expression  constrains that regular expression to match
			 a final segment of a line.

	  *	 A  regular  expression  (not  just	a	one-
			 character regular expression) followed by `*'
			 (an asterisk) is a  regular  expression  that
			 matches  zero or more occurrences of the one-
			 character regular expression.	If  there  is
			 any  choice, the longest leftmost string that
			 permits a match is chosen.

	  +	 A regular expression followed by `+' (a  plus
			 sign)  is  a  regular expression that matches
			 one or more occurrences of the  one-character
			 regular  expression.  If there is any choice,
			 the longest leftmost string  that  permits  a
			 match is chosen.

	  ?	 A regular expression followed by `?' (a ques-
			 tion  mark)  is  a  regular  expression  that
			 matches zero or one occurrences of  the  one-
			 character  regular  expression.	If there is
			 any choice, the longest leftmost string  that
			 permits a match is chosen.

	  |	 Alternation:	 two	 regular	 expressions
			 separated  by  `|'  or NEWLINE match either a
			 match for  the  first  or  a  match  for  the
			 second.

	  ()	A regular expression enclosed in  parentheses
			 matches a match for the regular expression.

	  The order of precedence of operators at the same parenthesis
	  level  is  `[ ]'  (character  classes),  then  `*'  `+'  `?'
	  (closures),then  concatenation,  then  `|'  (alternation)and
	  NEWLINE.
 
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