GAWK: Effective AWK Programming

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296 GAWK: Effective AWK ProgrammingNow comes the tedious part: filling in the array. Only a few of the calls are shown here,since they all follow the same pattern:/* fill in the array */aptr = assoc_lookup(array, tmp_string("name", 4), FALSE);*aptr = dupnode(file);aptr = assoc_lookup(array, tmp_string("mode", 4), FALSE);*aptr = make_number((AWKNUM) sbuf.st_mode);aptr = assoc_lookup(array, tmp_string("pmode", 5), FALSE);pmode = format_mode(sbuf.st_mode);*aptr = make_string(pmode, strlen(pmode));When done, we free the temporary value containing the file name, set the return value,and return:}free_temp(file);/* Set the return value */set_value(tmp_number((AWKNUM) ret));/* Just to make the interpreter happy */return tmp_number((AWKNUM) 0);Finally, it’s necessary to provide the “glue” that loads the new function(s) into gawk.By convention, each library has a routine named dlload that does the job:/* dlload --- load new builtins in this library */NODE *dlload(tree, dl)NODE *tree;void *dl;{make_builtin("chdir", do_chdir, 1);make_builtin("stat", do_stat, 2);return tmp_number((AWKNUM) 0);}And that’s it! As an exercise, consider adding functions to implement system calls suchas chown, chmod, and umask.C.3.2.3 Integrating the ExtensionsNow that the code is written, it must be possible to add it at runtime to the running gawkinterpreter. First, the code must be compiled. Assuming that the functions are in a filenamed ‘filefuncs.c’, and idir is the location of the gawk include files, the following stepscreate a GNU/Linux shared library:$ gcc -shared -DHAVE_CONFIG_H -c -O -g -Iidir filefuncs.c$ ld -o filefuncs.so -shared filefuncs.o
Appendix C: Implementation Notes 297Once the library exists, it is loaded by calling the extension built-in function. Thisfunction takes two arguments: the name of the library to load and the name of a functionto call when the library is first loaded. This function adds the new functions to gawk. Itreturns the value returned by the initialization function within the shared library:# file testff.awkBEGIN {extension("./filefuncs.so", "dlload")chdir(".")# no-op}data[1] = 1 # force ‘data’ to be an arrayprint "Info for testff.awk"ret = stat("testff.awk", data)print "ret =", retfor (i in data)printf "data[\"%s\"] = %s\n", i, data[i]print "testff.awk modified:",strftime("%m %d %y %H:%M:%S", data["mtime"])Here are the results of running the program:$ gawk -f testff.awk⊣ Info for testff.awk⊣ ret = 0⊣ data["blksize"] = 4096⊣ data["mtime"] = 932361936⊣ data["mode"] = 33188⊣ data["type"] = file⊣ data["dev"] = 2065⊣ data["gid"] = 10⊣ data["ino"] = 878597⊣ data["ctime"] = 971431797⊣ data["blocks"] = 2⊣ data["nlink"] = 1⊣ data["name"] = testff.awk⊣ data["atime"] = 971608519⊣ data["pmode"] = -rw-r--r--⊣ data["size"] = 607⊣ data["uid"] = 2076⊣ testff.awk modified: 07 19 99 08:25:36C.4 Probable Future ExtensionsAWK is a language similar to PERL, only considerably more elegant.Arnold RobbinsHey!Larry Wall
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