Compaq AA-PWCBD-TE manual Pat1 = Anchor + abc

DEC Text Processing Utility Data Types

3.7 Pattern Data Type

3.7.6 Anchoring a Pattern

Anchoring a pattern forces SEARCH or SEARCH_QUIETLY to match the anchored part of the pattern to text starting at the current search position. If the anchored part of a pattern fails to match that text, SEARCH or SEARCH_ QUIETLY stops searching.

Usually, all pattern elements other than the first pattern element of a pattern are anchored. This means that a pattern can match text starting at any point in the searched text but that once it starts matching, each pattern element must match the text immediately following the text that matched the previous pattern element.

To direct DECTPU to stop searching if the characters starting at the editing point do not match the pattern, use the ANCHOR keyword as the first pattern element. For example, the following pattern matches only if the string abc occurs at the editing point:

pat1 := ANCHOR + "abc";

There are two ways to unanchor pattern elements in the midst of a pattern. The easiest is to concatenate or link the UNANCHOR keyword before the pattern element you want to unanchor. The following pattern unanchors the pattern element xyz:

pat1 := "abc" + UNANCHOR + "xyz";

This means that the pattern pat1 matches any text beginning with the characters abc and ending with the characters xyz. It does not matter what or how many characters or line breaks appear between the two sets of characters. Since SEARCH or SEARCH_QUIETLY matches the first xyz it finds, the text between the two sets of characters by definition does not contain the string xyz.

The second way to unanchor a pattern element is to use the special properties of the link operator ( & ). While the concatenation operator always anchors the right pattern element to the left, the link operator does so only if the right pattern element is not a pattern variable. If the link operator’s right pattern element is a pattern variable, the link operator unanchors that pattern element. The pattern pat2 defined by the following assignments matches any sequence of text that begins with the letter a and ends with a digit.

pat1 := ANY ("0123456789"); pat2 := "a" & pat1;

Any amount of text can occur between the a and the digit. Pat2 matches the same text as the following pattern:

pat3 := "a" + UNANCHOR + ANY( "0123456789" );

The link operator unanchors a pattern variable regardless of what the left pattern element is. In particular, the following two patterns match the same text:

pat2 := "a" & pat1;

pat3 := "a" & ANCHOR & pat1;

If you are using pattern variables to form patterns and you wish those variables to be anchored, you have two choices: you can use the concatenation operator, or you can use the ANCHOR keyword as the first element of any pattern the pattern variables reference.

DEC Text Processing Utility Data Types 3–17