Class: Pattern

The Pattern built-ins implement a simplified and slightly modified subset of UNIX's regular expression pattern matching. They allow find patterns to be compiled for finding patterns within text, as well as change patterns which replacing that text as well.

A find pattern may consist of the following elements:

Any element of a find pattern may be 'tagged' with the angle brackets <>. The tagged elements are numbered 1..n from left to right and can be specially extracted from the return value of Pattern.Find() or specially referred to in a change pattern.

A character class consists of zero or more of the following elements, surrounded by brackets ([]):

Special meaning of characters in a character class is lost when escaped or for exclamation point (!) when it is not at the beginning, and dash (-) when it is not at the beginning or end of the character class.

A change pattern is used to map the results of a find pattern to some replacement patter, as for a find and replace operation. It consists of zero or more of the following elements:

In any pattern, an escape sequence consists of the character @ followed by a single character:

For those familiar with UNIX's regexp, use of OScript's pattern built-ins is easy keeping the following in mind:

• Use at sign @ instead of backslash (\) to escape characters.
• Use percent (%) instead of caret (^) to match beginning of line.
• Use exclamation point (!) instead of caret (^) to negate at the beginning of a character class.
• Use question mark (?) instead of dot (.) to match any character.
• Remember that OScript's patterns are a small subset and do not support composition, etc.

Here is an example of Pattern.Find() which retrieves name value pairs, formatted in a particular way (" name = value;"), from a data string:

String  target = 
    "<data> firstname   =  Mary;lastname =Joe; phone = 555-5555; address= 4 Some Lane, Nowhere, SS 99999; </data>"
String  search = " *<[A-Za-z]+> *= *<[!;]+>;"
String  s = target
PatFind finder = Pattern.CompileFind( search )
List    result = Pattern.Find( s, finder )

while ( IsDefined( result ) )
    Echo( result[ 4 ], ' = "', result[ 5 ], '"' )

    s = s[ result[ 2 ] : ]
    result = Pattern.Find( s, finder )
end

The output of the example is:

address = "4 Some Lane, Nowhere, SS 99999"
firstname = "Mary"
lastname = "Joe"
phone = "555-5555"

Here is an example of Pattern.Change() which operates on the same data, but instead produces an alteration of the input string with quoted data values and extraneous spaces removed:

String      target = 
    "<data> firstname   =  Mary;lastname =Joe; phone = 555-5555; address= 4 Some Lane, Nowhere, SS 99999; </data>"
String      search = " *<[A-Za-z]+> *= *<[!;]+>;"
String      change = '#1="#2";'
PatFind     finder = Pattern.CompileFind( search )
PatChange   replacer = Pattern.CompileChange( change )
String      result = Pattern.Change( target, finder, replacer )

Echo( "Input: ", target )
Echo( "Result: ", result )

The output of the example is:

Input:
    <data> firstname   =  Mary;lastname =Joe; phone = 555-5555; address= 4 Some Lane, Nowhere, SS 99999; </data>
Result:
    <data>firstname="Mary";lastname="Joe";phone="555-5555";address="4 Some Lane, Nowhere, SS 99999"; </data>