C.2.2 Adding New Features

You are free to add any new features you like to gawk. However, if you want your changes to be incorporated into the gawk distribution, there are several steps that you need to take in order to make it possible to include them:

1. Before building the new feature into gawk itself, consider writing it as an extension (see Dynamic Extensions). If that’s not possible, continue with the rest of the steps in this list.
2. Be prepared to sign the appropriate paperwork. In order for the FSF to distribute your changes, you must either place those changes in the public domain and submit a signed statement to that effect, or assign the copyright in your changes to the FSF. Both of these actions are easy to do and many people have done so already. If you have questions, please contact me (see Bugs), or “assign at gnu dot org”.
3. Get the latest version. It is much easier for me to integrate changes if they are relative to the most recent distributed version of gawk, or better yet, relative to the latest code in the Git repository. If your version of gawk is very old, I may not be able to integrate your changes at all. (See Getting, for information on getting the latest version of gawk.)
4. Follow the GNU Coding Standards. This document describes how GNU software should be written. If you haven’t read it, please do so, preferably before starting to modify gawk. (The GNU Coding Standards are available from the GNU Project’s website. Texinfo, Info, and DVI versions are also available.)
5. Use the gawk coding style. The C code for gawk follows the instructions in the GNU Coding Standards, with minor exceptions. The code is formatted using the traditional “K&R” style, particularly as regards to the placement of braces and the use of TABs. In brief, the coding rules for gawk are as follows:
   • Use ANSI/ISO style (prototype) function headers when defining functions.
   • Put the name of the function at the beginning of its own line.
   • Use ‘#elif’ instead of nesting ‘#if’ inside ‘#else’.
   • Put the return type of the function, even if it is int, on the line above the line with the name and arguments of the function.
   • Put spaces around parentheses used in control structures (if, while, for, do, switch, and return).
   • Do not put spaces in front of parentheses used in function calls.
   • Put spaces around all C operators and after commas in function calls.
   • Do not use the comma operator to produce multiple side effects, except in for loop initialization and increment parts, and in macro bodies.
   • Use real TABs for indenting, not spaces.
   • Use the “K&R” brace layout style.
   • Use comparisons against NULL and '\0' in the conditions of if, while, and for statements, as well as in the cases of switch statements, instead of just the plain pointer or character value.
   • Use true and false for bool values, the NULL symbolic constant for pointer values, and the character constant '\0' where appropriate, instead of 1 and 0.
   • Provide one-line descriptive comments for each function.
   • Do not use the alloca() function for allocating memory off the stack. Its use causes more portability trouble than is worth the minor benefit of not having to free the storage. Instead, use malloc() and free().
   • Do not use comparisons of the form ‘! strcmp(a, b)’ or similar. As Henry Spencer once said, “strcmp() is not a boolean!” Instead, use ‘strcmp(a, b) == 0’.
   • If adding new bit flag values, use explicit hexadecimal constants (0x001, 0x002, 0x004, and son on) instead of shifting one left by successive amounts (‘(1<<0)’, ‘(1<<1)’, and so on).

   NOTE: If I have to reformat your code to follow the coding style used in gawk, I may not bother to integrate your changes at all.

6. Update the documentation. Along with your new code, please supply new sections and/or chapters for this Web page. If at all possible, please use real Texinfo, instead of just supplying unformatted ASCII text (although even that is better than no documentation at all). Conventions to be followed in GAWK: Effective AWK Programming are provided after the ‘@bye’ at the end of the Texinfo source file. If possible, please update the man page as well.

   You will also have to sign paperwork for your documentation changes.

7. Submit changes as unified diffs. Use ‘diff -u -r -N’ to compare the original gawk source tree with your version. I recommend using the GNU version of diff, or best of all, ‘git diff’ or ‘git format-patch’. Send the output produced by diff to me when you submit your changes. (See Bugs, for the electronic mail information.)

   Using this format makes it easy for me to apply your changes to the master version of the gawk source code (using patch). If I have to apply the changes manually, using a text 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 further minimize the amount of work I have to do, making it easier for me to accept patches. It is simplest if you just make this part of your diff.

Although this sounds like a lot of work, please remember that while you may write the new code, I have to maintain it and support it. If it isn’t possible for me to do that with a minimum of extra work, then I probably will not.