/[pcre]/code/trunk/README

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-revision 33 by nigel,
Sat Feb 24 21:39:01 2007 UTC
+revision 35 by nigel,
Sat Feb 24 21:39:05 2007 UTC
 Line 16 
 README file for PCRE (Perl-compatible re
  * possible to pass over a pointer to character tables built in the current    *
  * locale by pcre_maketables(). To use the default tables, this new arguement  *
  * should be passed as NULL.                                                   *
+ *                                                                             *
+ *           IMPORTANT FOR THOSE UPGRADING FROM VERSION 2.05                   *
+ *                                                                             *
+ * Yet another (and again I hope this really is the last) change has been made *
+ * to the API for the pcre_exec() function. An additional argument has been    *
+ * added to make it possible to start the match other than at the start of the *
+ * subject string. This is important if there are lookbehinds. The new man     *
+ * page has the details, but you just want to convert existing programs, all   *
+ * you need to do is to stick in a new fifth argument to pcre_exec(), with a   *
+ * value of zero. For example, change                                          *
+ *                                                                             *
+ *   pcre_exec(pattern, extra, subject, length, options, ovec, ovecsize)       *
+ * to                                                                          *
+ *   pcre_exec(pattern, extra, subject, length, 0, options, ovec, ovecsize)    *
  *******************************************************************************
  The distribution should contain the following files:
    ChangeLog         log of changes to the code
-Line 45 
 The distribution should contain the foll
+Line 60 
 The distribution should contain the foll
    testinput2        test data for error messages and non-Perl things
    testinput3        test data, compatible with Perl 5.005
    testinput4        test data for locale-specific tests
-   testoutput1       test results corresponding to testinput
+   testoutput1       test results corresponding to testinput1
    testoutput2       test results corresponding to testinput2
    testoutput3       test results corresponding to testinput3
    testoutput4       test results corresponding to testinput4
-Line 112 
 Character tables
+Line 127 
 Character tables
  PCRE uses four tables for manipulating and identifying characters. The final
  argument of the pcre_compile() function is a pointer to a block of memory
- containing the concatenated tables. A call to pcre_maketables() is used to
+ containing the concatenated tables. A call to pcre_maketables() can be used to
- generate a set of tables in the current locale. However, if the final argument
+ generate a set of tables in the current locale. If the final argument for
- is passed as NULL, a set of default tables that is built into the binary is
+ pcre_compile() is passed as NULL, a set of default tables that is built into
- used.
+ the binary is used.
  The source file called chartables.c contains the default set of tables. This is
  not supplied in the distribution, but is built by the program dftables
  (compiled from dftables.c), which uses the ANSI C character handling functions
  such as isalnum(), isalpha(), isupper(), islower(), etc. to build the table
- sources. This means that the default C locale set your system will control the
+ sources. This means that the default C locale which is set for your system will
- contents of the tables. You can change the default tables by editing
+ control the contents of these default tables. You can change the default tables
- chartables.c and then re-building PCRE. If you do this, you should probably
+ by editing chartables.c and then re-building PCRE. If you do this, you should
- also edit Makefile to ensure that the file doesn't ever get re-generated.
+ probably also edit Makefile to ensure that the file doesn't ever get
+ re-generated.
  The first two 256-byte tables provide lower casing and case flipping functions,
  respectively. The next table consists of three 32-byte bit maps which identify
-Line 178 
 example,
+Line 194 
 example,
    /abc/\
- then a backslash is added to the end of the pattern. This provides a way of
+ then a backslash is added to the end of the pattern. This is done to provide a
- testing the error condition that arises if a pattern finishes with a backslash,
+ way of testing the error condition that arises if a pattern finishes with a
- because
+ backslash, because
    /abc\/
-Line 188 
 is interpreted as the first line of a pa
+Line 204 
 is interpreted as the first line of a pa
  pcretest to read the next line as a continuation of the regular expression.
  The pattern may be followed by i, m, s, or x to set the PCRE_CASELESS,
- PCRE_MULTILINE, PCRE_DOTALL, or PCRE_EXTENDED options, respectively. These
+ PCRE_MULTILINE, PCRE_DOTALL, or PCRE_EXTENDED options, respectively. For
- options have the same effect as they do in Perl.
+ example:
+   /caseless/i
- There are also some upper case options that do not match Perl options: /A, /E,
+ These modifier letters have the same effect as they do in Perl. There are
- and /X set PCRE_ANCHORED, PCRE_DOLLAR_ENDONLY, and PCRE_EXTRA respectively.
+ others which set PCRE options that do not correspond to anything in Perl: /A,
+ /E, and /X set PCRE_ANCHORED, PCRE_DOLLAR_ENDONLY, and PCRE_EXTRA respectively.
+ Searching for all possible matches within each subject string can be requested
+ by the /g or /G modifier. The /g modifier behaves similarly to the way it does
+ in Perl. After finding a match, PCRE is called again to search the remainder of
+ the subject string. The difference between /g and /G is that the former uses
+ the start_offset argument to pcre_exec() to start searching at a new point
+ within the entire string, whereas the latter passes over a shortened substring.
+ This makes a difference to the matching process if the pattern begins with a
+ lookbehind assertion (including \b or \B).
+ There are a number of other modifiers for controlling the way pcretest
+ operates.
+ The /+ modifier requests that as well as outputting the substring that matched
+ the entire pattern, pcretest should in addition output the remainder of the
+ subject string. This is useful for tests where the subject contains multiple
+ copies of the same substring.
- The /L option must be followed directly by the name of a locale, for example,
+ The /L modifier must be followed directly by the name of a locale, for example,
    /pattern/Lfr
- For this reason, it must be the last option letter. The given locale is set,
+ For this reason, it must be the last modifier letter. The given locale is set,
  pcre_maketables() is called to build a set of character tables for the locale,
  and this is then passed to pcre_compile() when compiling the regular
- expression. Without an /L option, NULL is passed as the tables pointer; that
+ expression. Without an /L modifier, NULL is passed as the tables pointer; that
  is, /L applies only to the expression on which it appears.
- The /I option requests that pcretest output information about the compiled
+ The /I modifier requests that pcretest output information about the compiled
  expression (whether it is anchored, has a fixed first character, and so on). It
  does this by calling pcre_info() after compiling an expression, and outputting
  the information it gets back. If the pattern is studied, the results of that
  are also output.
- The /D option is a PCRE debugging feature, which also assumes /I. It causes the
+ The /D modifier is a PCRE debugging feature, which also assumes /I. It causes
- internal form of compiled regular expressions to be output after compilation.
+ the internal form of compiled regular expressions to be output after
+ compilation.
- The /S option causes pcre_study() to be called after the expression has been
+ The /S modifier causes pcre_study() to be called after the expression has been
  compiled, and the results used when the expression is matched.
- The /M option causes information about the size of memory block used to hold
+ The /M modifier causes information about the size of memory block used to hold
  the compile pattern to be output.
- Finally, the /P option causes pcretest to call PCRE via the POSIX wrapper API
+ Finally, the /P modifier causes pcretest to call PCRE via the POSIX wrapper API
- rather than its native API. When this is done, all other options except /i and
+ rather than its native API. When this is done, all other modifiers except /i,
- /m are ignored. REG_ICASE is set if /i is present, and REG_NEWLINE is set if /m
+ /m, and /+ are ignored. REG_ICASE is set if /i is present, and REG_NEWLINE is
- is present. The wrapper functions force PCRE_DOLLAR_ENDONLY always, and
+ set if /m is present. The wrapper functions force PCRE_DOLLAR_ENDONLY always,
- PCRE_DOTALL unless REG_NEWLINE is set.
+ and PCRE_DOTALL unless REG_NEWLINE is set.
  Before each data line is passed to pcre_exec(), leading and trailing whitespace
  is removed, and it is then scanned for \ escapes. The following are recognized:
-Line 263 
 pcre_exec() returns, starting with numbe
+Line 300 
 pcre_exec() returns, starting with numbe
  whole pattern. Here is an example of an interactive pcretest run.
    $ pcretest
-   Testing Perl-Compatible Regular Expressions
+   PCRE version 2.06 08-Jun-1999
-   PCRE version 0.90 08-Sep-1997
      re> /^abc(\d+)/
    data> abc123
 : abc123
 : 123
    data> xyz
    No match
+ If the strings contain any non-printing characters, they are output as \0x
+ escapes. If the pattern has the /+ modifier, then the output for substring 0 is
+ followed by the the rest of the subject string, identified by "0+" like this:
+     re> /cat/+
+   data> cataract
+: cat
++ aract
+ If the pattern has the /g or /G modifier, the results of successive matching
+ attempts are output in sequence, like this:
+     re> /\Bi(\w\w)/g
+   data> Mississippi
+: iss
+: ss
+: iss
+: ss
+: ipp
+: pp
+ "No match" is output only if the first match attempt fails.
  If any of \C, \G, or \L are present in a data line that is successfully
  matched, the substrings extracted by the convenience functions are output with
  C, G, or L after the string number instead of a colon. This is in addition to
-Line 313 
 The perltest program
+Line 372 
 The perltest program
  The perltest program tests Perl's regular expressions; it has the same
  specification as pcretest, and so can be given identical input, except that
- input patterns can be followed only by Perl's lower case options. The contents
+ input patterns can be followed only by Perl's lower case modifiers. The
- of testinput1 and testinput3 meet this condition.
+ contents of testinput1 and testinput3 meet this condition.
  The data lines are processed as Perl strings, so if they contain $ or @
  characters, these have to be escaped. For this reason, all such characters in
- the testinput file are escaped so that it can be used for perltest as well as
+ testinput1 and testinput3 are escaped so that they can be used for perltest as
- for pcretest, and the special upper case options such as /A that pcretest
+ well as for pcretest, and the special upper case modifiers such as /A that
- recognizes are not used in this file. The output should be identical, apart
+ pcretest recognizes are not used in these files. The output should be
- from the initial identifying banner.
+ identical, apart from the initial identifying banner.
- The testinput2 and testinput4 files are not suitable for feeding to Perltest,
+ The testinput2 and testinput4 files are not suitable for feeding to perltest,
- since they do make use of the special upper case options and escapes that
+ since they do make use of the special upper case modifiers and escapes that
  pcretest uses to test some features of PCRE. The first of these files also
  contains malformed regular expressions, in order to check that PCRE diagnoses
  them correctly.
  Philip Hazel <ph10@cam.ac.uk>
- April 1999
+ June 1999

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