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ABENREGEX_PCRE_SYNTAX - REGEX PCRE SYNTAX

ABENREGEX_PCRE_SYNTAX - REGEX PCRE SYNTAX

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- PCRE Syntax

Regular expressions with PCRE syntax can be specified after the addition PCRE of the statements FIND and REPLACE and the argument pcre of built-in functions for strings. Objects for PCRE regular expressions can be created with the factory method CREATE_PCRE of the system class CL_ABAP_REGEX to be used in statements FIND and REPLACE or with the system class CL_ABAP_MATCHER.

Currently, there is no detailed description of the PCRE syntax for regular expressions in the ABAP keyword documentation.

  • For a short syntax overview, see
Special Characters in PCRE Regular Expressions
  • For the complete documentation, please refer to:
Perl documentation perlre

A regular expression in PCRE syntax can be compiled in a normal or extended mode. In the extended mode, most unescaped whitespace characters (blanks and line breaks) of the pattern are ignored outside character classes and comments can be placed behind #. In ABAP statements and built-in functions, the extended mode is switched on by default and can be switched off with (?-x) in the regular expression. When using CL_ABAP_REGEX, it can be switched by the parameter EXTENDED of method CREATE_PCRE.

For regular expressions in PCRE syntax, it can be defined whether valid UTF-16 character strings are expected or not. In ABAP statements and built-in functions, a PCRE regular expression can be introduced with (*UTF) in order to check for valid UTF-16 strings. When using CL_ABAP_REGEX, the parameter UNICODE_HANDLING of method CREATE_PCRE can be used. When the strict mode for working with UTF-16 strings is switched on, a surrogate pair is handled as a single character (see example for counting).

Notes

  • The PCRE syntax supports callouts that call ABAP methods during matching an regular expression with CL_ABAP_MATCHER.
  • The test and demonstration program DEMO_REGEX allows PCRE syntax to be tested by selecting PCRE.

Example

Searching for a PCRE regular expression in a character string. See also the program DEMO_FIND_REGEX.

Example

PCRE regular expressions support non-greedy behavior by placing a question mark (?) behind quantifiers as for example the wildcard character asterisk (*). In the following example, the asterisk in the first regular expression is greedy and finds everything between the first <i> and the last /i>. In the second regular expression, the asterisk is marked as non-greedy and only the substring between the first <i> and the following /i> is found. Non-greedy behavior is not supported in the obsolete POSIX syntax and other workarounds as for example [^<]* have to be used. For more information, see New features in PCRE compared to POSIX.

Example

This example shows the effect of the extended mode, that is switched on by default and might lead to unexpected results. All replacements yield the same result a-b except the one in r5, where the line break character is not found but instead all empty spaces are replaced by the replacement character -. The reason is that the pattern |\n| consists of nothing but the line break character and this is ignored in the extended mode. Therefore, the pattern is in fact an empty string and yields the same result as specifying an empty string directly. By switching of the extended mode with (?-x), the line break character is not ignored an yields the same result as the special PCRE character \n, which is expressed in different ways here.

Copyright Note

This software uses the PCRE2 library under the PCRE2 LICENCE.






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