GAWK: Effective AWK Programming

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286 GAWK: Effective AWK Programming7. Submit changes as context diffs or unified diffs. Use ‘diff -c -r -N’ or ‘diff -u -r-N’ to compare the original gawk source tree with your version. (I find context diffs tobe more readable but unified diffs are more compact.) I recommend using the GNUversion of diff. Send the output produced by either run of diff to me when yousubmit your changes. (See Section B.5 [Reporting Problems and Bugs], page 280, forthe electronic mail information.)Using this format makes it easy for me to apply your changes to the master version ofthe gawk source code (using patch). If I have to apply the changes manually, using atext editor, I may not do so, particularly if there are lots of changes.8. Include an entry for the ‘ChangeLog’ file with your submission. This helps furtherminimize the amount of work I have to do, making it easier for me to accept patches.Although this sounds like a lot of work, please remember that while you may write thenew code, I have to maintain it and support it. If it isn’t possible for me to do that with aminimum of extra work, then I probably will not.C.2.2 Porting gawk to a New Operating SystemIf you want to port gawk to a new operating system, there are several steps:1. Follow the guidelines in the previous section concerning coding style, submission ofdiffs, and so on.2. When doing a port, bear in mind that your code must coexist peacefully with the restof gawk and the other ports. Avoid gratuitous changes to the system-independent partsof the code. If at all possible, avoid sprinkling ‘#ifdef’s just for your port throughoutthe code.If the changes needed for a particular system affect too much of the code, I probablywill not accept them. In such a case, you can, of course, distribute your changes onyour own, as long as you comply with the GPL (see [GNU General Public License],page 316).3. A number of the files that come with gawk are maintained by other people at theFree Software Foundation. Thus, you should not change them unless it is for a verygood reason; i.e., changes are not out of the question, but changes to these filesare scrutinized extra carefully. The files are ‘getopt.h’, ‘getopt.c’, ‘getopt1.c’,‘regex.h’, ‘regex.c’, ‘regcomp.c’, ‘regex_internal.c’, ‘regex_internal.h’,‘regexec.c’, ‘dfa.h’, ‘dfa.c’, ‘install-sh’, and ‘mkinstalldirs’.4. Be willing to continue to maintain the port. Non-Unix operating systems are supportedby volunteers who maintain the code needed to compile and run gawk on their systems.If noone volunteers to maintain a port, it becomes unsupported and it may be necessaryto remove it from the distribution.5. Supply an appropriate ‘gawkmisc.???’ file. Each port has its own ‘gawkmisc.???’that implements certain operating system specific functions. This is cleaner than aplethora of ‘#ifdef’s scattered throughout the code. The ‘gawkmisc.c’ in the mainsource directory includes the appropriate ‘gawkmisc.???’ file from each subdirectory.Be sure to update it as well.Each port’s ‘gawkmisc.???’ file has a suffix reminiscent of the machine or operatingsystem for the port—for example, ‘pc/gawkmisc.pc’ and ‘vms/gawkmisc.vms’. The
Appendix C: Implementation Notes 287use of separate suffixes, instead of plain ‘gawkmisc.c’, makes it possible to move filesfrom a port’s subdirectory into the main subdirectory, without accidentally destroyingthe real ‘gawkmisc.c’ file. (Currently, this is only an issue for the PC operating systemports.)6. Supply a ‘Makefile’ as well as any other C source and header files that are necessary foryour operating system. All your code should be in a separate subdirectory, with a namethat is the same as, or reminiscent of, either your operating system or the computersystem. If possible, try to structure things so that it is not necessary to move files outof the subdirectory into the main source directory. If that is not possible, then be sureto avoid using names for your files that duplicate the names of files in the main sourcedirectory.7. Update the documentation. Please write a section (or sections) for this book describingthe installation and compilation steps needed to compile and/or install gawk for yoursystem.8. Be prepared to sign the appropriate paperwork. In order for the FSF to distributeyour code, you must either place your code in the public domain and submit a signedstatement to that effect, or assign the copyright in your code to the FSF.Following these steps makes it much easier to integrate your changes into gawk and havethem coexist happily with other operating systems’ code that is already there.In the code that you supply and maintain, feel free to use a coding style and brace layoutthat suits your taste.C.3 Adding New Built-in Functions to gawkDanger Will Robinson! Danger!!Warning! Warning!The RobotBeginning with gawk 3.1, it is possible to add new built-in functions to gawk usingdynamically loaded libraries. This facility is available on systems (such as GNU/Linux)that support the dlopen and dlsym functions. This section describes how to write anduse dynamically loaded extensions for gawk. Experience with programming in C or C++ isnecessary when reading this section.Caution: The facilities described in this section are very much subject to change in afuture gawk release. Be aware that you may have to re-do everything, perhaps from scratch,at some future time.Caution: If you have written your own dynamic extensions, be sure to recompile themfor each new gawk release. There is no guarantee of binary compatibility between differentreleases, nor will there ever be such a guarantee.C.3.1 A Minimal Introduction to gawk InternalsThe truth is that gawk was not designed for simple extensibility. The facilities for addingfunctions using shared libraries work, but are something of a “bag on the side.” Thus, thistour is brief and simplistic; would-be gawk hackers are encouraged to spend some time readingthe source code before trying to write extensions based on the material presented here.Of particular note are the files ‘awk.h’, ‘builtin.c’, and ‘eval.c’. Reading ‘awkgram.y’in order to see how the parse tree is built would also be of use.
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