Simplifed use of Regular Expressions from within your Scripts

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Introduction

Knowing the Regular Expression-capabilities and -syntax of Perl, I wanted to have a similar syntax from within my VBScript code. VBScript uses the RegExp object, so I wrapped the calls to the RegExp object inside three function.

Functions

rxTest

function rxTest( text, pattern, flags )

Use this function to test for a pattern inside a string. Acts similar to the =~ s// operator in Perl.

The arguments are:

• text
  The text string upon which the regular expression is executed.
• pattern
  Regular string expression being searched for.
• flags
i: case insensitive, g: global, m: multiline

Returns true if found, false if not found.

rxReplace

function rxReplace( text, pattern, replace_text, flags )

Use this function to replace a pattern inside a string with another string. Acts similar to the =~ m// operator in Perl.

The arguments are:

• text
  The text string upon which the regular expression is executed.
• pattern
  Regular string expression being searched for.
• replace_text
  The replacement text string.
• flags
i: case insensitive, g: global, m: multiline

Returns the modified string. The input-string is not modified by this function.

rxExec

function rxExec( text, pattern, flags )

Use this function to test for a pattern inside a string and return the matched elements. Acts similar to the =~ s// operator in Perl.

The arguments are:

• text
  The text string upon which the regular expression is executed.
• pattern
  Regular string expression being searched for.
• flags
i: case insensitive, g: global, m: multiline

Returns a Matches collection if a match is found, otherwise returns nothing.

Examples

• Check whether a given URL starts with a certain protocol

  dim is_absolute
  is_absolute = rxTest( url, "^(https|http|ftp|mailto|javascript|jscript)://", "gis" )

• Remove a certain HTML tag from a string (stupid simple version!)

  dim blank
  blank = rxReplace( html, "<"&tag_name&"\b[^>]*>", "", "gi")

• Replace all ocurrences of a certain syntax by a value, looked up from a database

  do
    set matches = rxExec(html, "oid://([0-9]+)", "g")
  
    if not IsNothing(matches) then
      if matches.Count>0 then
        set match = matches(0)
  
        dim replacement
        if match.SubMatches.Count>0 then
          replacement = GetNameFromDatabaseByID(match.SubMatches(0))
        else
          replacement = ""
        end if
  
        html = Replace(html, match.Value, replacement)
      else
        exit do
      end if
    else
      exit do
    end if
  loop

The last example uses the function IsNothing which is defined as followed:

function IsNothing( byref obj )
	IsNothing = CBool(LCase(TypeName(obj))="nothing")
end function