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1  The files in the "maintain" directory of the PCRE source contain data, scripts,  MAINTENANCE README FOR PCRE
2  and programs that are used for the maintenance of PCRE, but do not form part of  ===========================
3  the PCRE distribution tarballs.  
4    The files in the "maint" directory of the PCRE source contain data, scripts,
5  132html         A Perl script that converts a .1 or .3 man page into HTML. It  and programs that are used for the maintenance of PCRE, but which do not form
6                  is called from MakeRelease. It "knows" the relevant troff  part of the PCRE distribution tarballs. This document describes these files and
7                  constructs that are used in the PCRE man pages.  also contains some notes for maintainers. Its contents are:
9  Builducptable   A Perl script that creates the contents of the ucptable.h file    Files in the maint directory
10                  from two Unicode data files, which themselves are downloaded    Updating to a new Unicode release
11                  from the Unicode web site. Run this script in the "maintain"    Preparing for a PCRE release
12                  directory.    Making a PCRE release
13      Long-term ideas (wish list)
14  CleanTxt        A Perl script that cleans up the output of "nroff -man" by  
15                  removing backspaces and other redundant text so as to produce  
16                  a readable .txt file. It is called from MakeRelease.  Files in the maint directory
17    ============================
18  Detrail         A Perl script that removes trailing spaces from files. It is  
19                  called from MakeRelease.  ---------------- This file is now OBSOLETE and no longer used ----------------
20    Builducptable    A Perl script that creates the contents of the ucptable.h file
21  Index.html      A file that is copied as index.html into the doc/html                   from two Unicode data files, which themselves are downloaded
22                  directory when the HTML documentation is being built. It works                   from the Unicode web site. Run this script in the "maint"
23                  like this so that doc/html can be deleted and re-created from                   directory.
24                  scratch.  ---------------- This file is now OBSOLETE and no longer used ----------------
26  MakeRelease     My script for creating a new release. It processes the  GenerateUtt.py   A Python script to generate part of the pcre_tables.c file
27                  documentation man pages into .text and HTML formats before                   that contains Unicode script names in a long string with
28                  creating tarballs and putting them in the Releases directory.                   offsets, which is tedious to maintain by hand.
30  Tech.Notes      Some notes about the internals of the PCRE code.  ManyConfigTests  A shell script that runs "configure, make, test" a number of
31                     times with different configuration settings.
32  Unicode.tables  The files in this directory, Scripts.txt and UnicodeData.txt,  
33                  were downloaded from the Unicode web site. They contain  MultiStage2.py   A Python script that generates the file pcre_ucd.c from three
34                  information about Unicode characters and scripts.                   Unicode data tables, which are themselves downloaded from the
35                     Unicode web site. Run this script in the "maint" directory.
36  ucptest.c       A short C program for testing the Unicode property functions in                   The generated file contains the tables for a 2-stage lookup
37                  pcre_ucp_searchfuncs.c, mainly useful after rebuilding the                   of Unicode properties.
38                  Unicode property table. Compile and run this in the "maintain"  
39                  directory.  pcre_chartables.c.non-standard
40                     This is a set of character tables that came from a Windows
41  ucptestdata     A directory containing two files, testinput1 and testoutput1,                   system. It has characters greater than 128 that are set as
42                  to use in conjunction with the ucptest program.                   spaces, amongst other things. I kept it so that it can be
43                     used for testing from time to time.
44  utf8.c          A short, freestanding C program for converting a Unicode code  
45                  point into a sequence of bytes in the UTF-8 encoding, and vice  README           This file.
46                  versa. If its argument is a hex number such as 0x1234, it  
47                  outputs a list of the equivalent UTF-8 bytes. If its argument  Unicode.tables   The files in this directory (CaseFolding.txt,
48                  is sequence of concatenated UTF-8 bytes (e.g. e188b4) it treats                   DerivedGeneralCategory.txt, GraphemeBreakProperty.txt,
49                  them as a UTF-8 character and outputs the equivalent code point                   Scripts.txt and UnicodeData.txt) were downloaded from the
50                  in hex.                   Unicode web site. They contain information about Unicode
51                     characters and scripts.
52  When there is a new release of Unicode, the files in Unicode.tables must be  
53  refreshed from the web site, and the Buildupctable script can then be run to  ucptest.c        A short C program for testing the Unicode property macros
54  generate a new version of ucptable.h. The ucptest program can be used to check                   that do lookups in the pcre_ucd.c data, mainly useful after
55  that the resulting table works properly, using the data files in ucptestdata to                   rebuilding the Unicode property table. Compile and run this in
56  check a number of test characters.                   the "maint" directory (see comments at its head).
58  ****  ucptestdata      A directory containing two files, testinput1 and testoutput1,
59                     to use in conjunction with the ucptest program.
61    utf8.c           A short, freestanding C program for converting a Unicode code
62                     point into a sequence of bytes in the UTF-8 encoding, and vice
63                     versa. If its argument is a hex number such as 0x1234, it
64                     outputs a list of the equivalent UTF-8 bytes. If its argument
65                     is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
66                     treats them as a UTF-8 character and outputs the equivalent
67                     code point in hex.
70    Updating to a new Unicode release
71    =================================
73    When there is a new release of Unicode, the files in Unicode.tables must be
74    refreshed from the web site. If the new version of Unicode adds new character
75    scripts, the source file ucp.h and both the MultiStage2.py and the
76    GenerateUtt.py scripts must be edited to add the new names. Then MultiStage2.py
77    can be run to generate a new version of pcre_ucd.c, and GenerateUtt.py can be
78    run to generate the tricky tables for inclusion in pcre_tables.c.
80    If MultiStage2.py gives the error "ValueError: list.index(x): x not in list",
81    the cause is usually a missing (or misspelt) name in the list of scripts. I
82    couldn't find a straightforward list of scripts on the Unicode site, but
83    there's a useful Wikipedia page that list them, and notes the Unicode version
84    in which they were introduced:
86    http://en.wikipedia.org/wiki/Unicode_scripts#Table_of_Unicode_scripts
88    The ucptest program can be compiled and used to check that the new tables in
89    pcre_ucd.c work properly, using the data files in ucptestdata to check a number
90    of test characters. The source file ucptest.c must be updated whenever new
91    Unicode script names are added.
93    Note also that both the pcresyntax.3 and pcrepattern.3 man pages contain lists
94    of Unicode script names.
97    Preparing for a PCRE release
98    ============================
100    This section contains a checklist of things that I consult before building a
101    distribution for a new release.
103    . Ensure that the version number and version date are correct in configure.ac.
105    . Update the library version numbers in configure.ac according to the rules
106      given below.
108    . If new build options have been added, ensure that they are added to the CMake
109      files as well as to the autoconf files. The relevant files are CMakeLists.txt
110      and config-cmake.h.in. After making a release tarball, test it out with CMake
111      if there have been changes here.
113    . Run ./autogen.sh to ensure everything is up-to-date.
115    . Compile and test with many different config options, and combinations of
116      options. Also, test with valgrind by running "RunTest valgrind" and
117      "RunGrepTest valgrind" (which takes quite a long time). The script
118      maint/ManyConfigTests now encapsulates this testing. It runs tests with
119      different configurations, and it also runs some of them with valgrind, all of
120      which can take quite some time.
122    . Run perltest.pl on the test data for tests 1, 4, and 6. The output
123      should match the PCRE test output, apart from the version identification at
124      the start of each test. The other tests are not Perl-compatible (they use
125      various PCRE-specific features or options).
127    . It is possible to test with the emulated memmove() function by undefining
128      HAVE_MEMMOVE and HAVE_BCOPY in config.h, though I do not do this often. You
129      may see a number of "pcre_memmove defined but not used" warnings for the
130      modules in which there is no call to memmove(). These can be ignored.
132    . Documentation: check AUTHORS, ChangeLog (check version and date), LICENCE,
133      NEWS (check version and date), NON-AUTOTOOLS-BUILD, and README. Many of these
134      won't need changing, but over the long term things do change.
136    . I used to test new releases myself on a number of different operating
137      systems, using different compilers as well. For example, on Solaris it is
138      helpful to test using Sun's cc compiler as a change from gcc. Adding
139      -xarch=v9 to the cc options does a 64-bit test, but it also needs -S 64 for
140      pcretest to increase the stack size for test 2. Since I retired I can no
141      longer do this, but instead I rely on putting out release candidates for
142      folks on the pcre-dev list to test.
145    Updating version info for libtool
146    =================================
148    This set of rules for updating library version information came from a web page
149    whose URL I have forgotten. The version information consists of three parts:
150    (current, revision, age).
152    1. Start with version information of 0:0:0 for each libtool library.
154    2. Update the version information only immediately before a public release of
155       your software. More frequent updates are unnecessary, and only guarantee
156       that the current interface number gets larger faster.
158    3. If the library source code has changed at all since the last update, then
159       increment revision; c:r:a becomes c:r+1:a.
161    4. If any interfaces have been added, removed, or changed since the last
162       update, increment current, and set revision to 0.
164    5. If any interfaces have been added since the last public release, then
165       increment age.
167    6. If any interfaces have been removed or changed since the last public
168       release, then set age to 0.
170    The following explanation may help in understanding the above rules a bit
171    better. Consider that there are three possible kinds of reaction from users to
172    changes in a shared library:
174    1. Programs using the previous version may use the new version as a drop-in
175       replacement, and programs using the new version can also work with the
176       previous one. In other words, no recompiling nor relinking is needed. In
177       this case, increment revision only, don't touch current or age.
179    2. Programs using the previous version may use the new version as a drop-in
180       replacement, but programs using the new version may use APIs not present in
181       the previous one. In other words, a program linking against the new version
182       may fail if linked against the old version at run time. In this case, set
183       revision to 0, increment current and age.
185    3. Programs may need to be changed, recompiled, relinked in order to use the
186       new version. Increment current, set revision and age to 0.
189    Making a PCRE release
190    =====================
192    Run PrepareRelease and commit the files that it changes (by removing trailing
193    spaces). The first thing this script does is to run CheckMan on the man pages;
194    if it finds any markup errors, it reports them and then aborts.
196    Once PrepareRelease has run clean, run "make distcheck" to create the tarballs
197    and the zipball. Double-check with "svn status", then create an SVN tagged
198    copy:
200      svn copy svn://vcs.exim.org/pcre/code/trunk \
201               svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
203    Don't forget to update Freshmeat when the new release is out, and to tell
204    webmaster@pcre.org and the mailing list. Also, update the list of version
205    numbers in Bugzilla (edit products).
208    Future ideas (wish list)
209    ========================
211    This section records a list of ideas so that they do not get forgotten. They
212    vary enormously in their usefulness and potential for implementation. Some are
213    very sensible; some are rather wacky. Some have been on this list for years;
214    others are relatively new.
216    . Optimization
218      There are always ideas for new optimizations so as to speed up pattern
219      matching. Most of them try to save work by recognizing a non-match without
220      having to scan all the possibilities. These are some that I've recorded:
222      * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
223        slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
224        OTOH, this is pathological - the user could easily fix it.
226      * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
227        to have little effect, and maybe makes things worse.
229      * "Ends with literal string" - note that a single character doesn't gain much
230        over the existing "required byte" (reqbyte) feature that just remembers one
231        data unit.
233      * These probably need to go in pcre_study():
235        o Remember an initial string rather than just 1 char?
237        o A required data unit from alternatives - not just the last unit, but an
238          earlier one if common to all alternatives.
240        o Friedl contains other ideas.
242      * pcre_study() does not set initial byte flags for Unicode property types
243        such as \p; I don't know how much benefit there would be for, for example,
244        setting the bits for 0-9 and all bytes >= xC0 when a pattern starts with
245        \p{N}.
247      * There is scope for more "auto-possessifying" in connection with \p and \P.
249    . If Perl gets to a consistent state over the settings of capturing sub-
250      patterns inside repeats, see if we can match it. One example of the
251      difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
252      leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
253      because I think it needs much more state to be remembered.
255    . Perl 6 will be a revolution. Is it a revolution too far for PCRE?
257    . Allow errorptr and erroroffset to be NULL. I don't like this idea.
259    . Line endings:
261      * Option to use NUL as a line terminator in subject strings. This could now
262        be done relatively easily since the extension to support LF, CR, and CRLF.
263        If it is done, a suitable option for pcregrep is also required.
265    . Option to provide the pattern with a length instead of with a NUL terminator.
266      This affects quite a few places in the code and is not trivial.
268    . Catch SIGSEGV for stack overflows?
270    . A feature to suspend a match via a callout was once requested.
272    . Option to convert results into character offsets and character lengths.
274    . Option for pcregrep to scan only the start of a file. I am not keen - this is
275      the job of "head".
277    . A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
278      preceded by a blank line, instead of adding it to every matched line, and (b)
279      support --outputfile=name.
281    . Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
282      (And now presumably UTF-16 and UCP for the 16-bit library, and UTF-32 and UCP
283      for the 32-bit library.)
285    . Add a user pointer to pcre_malloc/free functions -- some option would be
286      needed to retain backward compatibility.
288    . Define a union for the results from pcre_fullinfo().
290    . Provide a "random access to the subject" facility so that the way in which it
291      is stored is independent of PCRE. For efficiency, it probably isn't possible
292      to switch this dynamically. It would have to be specified when PCRE was
293      compiled. PCRE would then call a function every time it wanted a character.
295    . Wild thought: the ability to compile from PCRE's internal byte code to a real
296      FSM and a very fast (third) matcher to process the result. There would be
297      even more restrictions than for pcre_dfa_exec(), however. This is not easy.
298      This is probably obsolete now that we have the JIT support.
300    . Should pcretest have some private locale data, to avoid relying on the
301      available locales for the test data, since different OS have different ideas?
302      This won't be as thorough a test, but perhaps that doesn't really matter.
304    . pcregrep: add -rs for a sorted recurse? Having to store file names and sort
305      them will of course slow it down.
307    . Someone suggested --disable-callout to save code space when callouts are
308      never wanted. This seems rather marginal.
310    . Check names that consist entirely of digits: PCRE allows, but do Perl and
311      Python, etc?
313    . A user suggested a parameter to limit the length of string matched, for
314      example if the parameter is N, the current match should fail if the matched
315      substring exceeds N. This could apply to both match functions. The value
316      could be a new field in the extra block.
318    . Callouts with arguments: (?Cn:ARG) for instance.
320    . A user is going to supply a patch to generalize the API for user-specific
321      memory allocation so that it is more flexible in threaded environments. This
322      was promised a long time ago, and never appeared. However, this is a live
323      issue not only for threaded environments, but for libraries that use PCRE and
324      want not to be beholden to their caller's memory allocation.
326    . Write a wrapper to maintain a structure with specified runtime parameters,
327      such as recurse limit, and pass these to PCRE each time it is called. Also
328      maybe malloc and free. A user sent a prototype. This relates the the previous
329      item.
331    . Write a function that generates random matching strings for a compiled regex.
333    . Pcregrep: an option to specify the output line separator, either as a string
334      or select from a fixed list. This is not dead easy, because at the moment it
335      outputs whatever is in the input file.
337    . Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
338      non-thread-safe patch showed that this can help performance for patterns
339      where there are many alternatives. However, a simple thread-safe
340      implementation that I tried made things worse in many simple cases, so this
341      is not an obviously good thing.
343    . PCRE cannot at present distinguish between subpatterns with different names,
344      but the same number (created by the use of ?|). In order to do so, a way of
345      remembering *which* subpattern numbered n matched is needed. Bugzilla #760.
346      Now that (*MARK) has been implemented, it can perhaps be used as a way round
347      this problem.
349    . Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
350      "something" and the the #ifdef appears only in one place, in "something".
352    Philip Hazel
353    Email local part: ph10
354    Email domain: cam.ac.uk
355    Last updated: 09 November 2012

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