Compaq AA-PWCBD-TE manual Pattern Alternation Operator, 3.4 @ Partial Pattern Assignment Operator

DEC Text Processing Utility Data Types

3.7 Pattern Data Type

Given this sequence of definitions, a search for pat_var succeeds if DECTPU encounters the following string:

a5xcd

Because two pattern variables are linked, DECTPU searches first for the text that matches p1, then unanchors the search, and then searches for the text that matches p2.

To specify an anchored search when the right-hand subpattern is a pattern or keyword variable, use a plus sign ( + ). You must use a plus sign ( + ) to anchor the search if the right-hand subpattern is a keyword variable. If the right-hand subpattern is a pattern variable, you can use the ANCHOR keyword as the first element of that subpattern to anchor the right-hand subpattern.

For example, suppose you defined the following patterns:

p1 := LINE_BEGIN + "a";

p2 := "b" + LINE_END;

You anchor the search for p2 by using ( + ) as follows:

pat_var := p1 + p2;

If you use an ampersand ( & ), you unanchor the search for p2.

You can also anchor the search for p2 by defining p2 as follows:

p2 := ANCHOR + "b" + LINE_END;

3.7.3.3 (Pattern Alternation Operator)

The alternation operator ( ) tells SEARCH or SEARCH_QUIETLY to match a sequence of characters if those characters match either of the pattern elements separated by the alternation operator. The following pattern matches either the string abc or the string xes:

pat1 := "abc" "xes";

If the text being searched contains text that matches both alternatives, SEARCH or SEARCH_QUIETLY matches the earliest occurring match. If two matches start at the same character, SEARCH or SEARCH_QUIETLY matches the left element. For example, suppose you had the search text abcd and the following pattern definitions:

pat1 := "abc"		"bcd";
pat2 := "bcd"		"abc";
pat3 :=	"bc"	"bcd";
pat4 :=	"bcd"	"bc";

Given these definitions and search text, a search for the patterns pat1 and pat2 would return a range that contains the text abc. A search for the pattern pat3 would return a range that contains the text bc. Finally, a search for the pattern pat4 would return a range that contains the text bcd.

3.7.3.4 @ (Partial Pattern Assignment Operator)

The partial pattern assignment operator ( @ ) tells SEARCH or SEARCH_ QUIETLY to create a range that contains the text matching the pattern element to the left of the partial pattern assignment operator. When the search is completed, the variable to the right of the partial pattern assignment operator references the created range. If SEARCH or SEARCH_QUIETLY is given the search text abcdefg and the following pattern, it returns a range that contains the text abcdefg:

3–14DEC Text Processing Utility Data Types