GAWK: Effective AWK Programming

More documents

Recommendations

Info

206 GAWK: Effective AWK Programmingerror x -- invalid option⊣ c = , optarg = ⊣ non-option arguments:⊣ ARGV[4] = ⊣ ARGV[5] = In both runs, the first ‘--’ terminates the arguments to awk, so that it does not try tointerpret the ‘-a’, etc., as its own options.NOTE: After getopt is through, it is the responsibility of the user level codeto clear out all the elements of ARGV from 1 to Optind, so that awk does not tryto process the command-line options as file names.Several of the sample programs presented in Chapter 13 [Practical awk Programs],page 215, use getopt to process their arguments.12.5 Reading the User DatabaseThe PROCINFO array (see Section 6.5 [Built-in Variables], page 110) provides access to thecurrent user’s real and effective user and group ID numbers, and if available, the user’ssupplementary group set. However, because these are numbers, they do not provide veryuseful information to the average user. There needs to be some way to find the userinformation associated with the user and group ID numbers. This section presents a suiteof functions for retrieving information from the user database. See Section 12.6 [Readingthe Group Database], page 210, for a similar suite that retrieves information from the groupdatabase.The POSIX standard does not define the file where user information is kept. Instead,it provides the header file and several C language subroutines for obtaining userinformation. The primary function is getpwent, for “get password entry.” The “password”comes from the original user database file, ‘/etc/passwd’, which stores user information,along with the encrypted passwords (hence the name).While an awk program could simply read ‘/etc/passwd’ directly, this file may not containcomplete information about the system’s set of users. 7 To be sure you are able to producea readable and complete version of the user database, it is necessary to write a small Cprogram that calls getpwent. getpwent is defined as returning a pointer to a structpasswd. Each time it is called, it returns the next entry in the database. When thereare no more entries, it returns NULL, the null pointer. When this happens, the C programshould call endpwent to close the database. Following is pwcat, a C program that “cats”the password database:/** pwcat.c** Generate a printable version of the password database*/#include #include 7 It is often the case that password information is stored in a network database.
Chapter 12: A Library of awk Functions 207intmain(argc, argv)int argc;char **argv;{struct passwd *p;}while ((p = getpwent()) != NULL)printf("%s:%s:%ld:%ld:%s:%s:%s\n",p->pw_name, p->pw_passwd, (long) p->pw_uid,(long) p->pw_gid, p->pw_gecos, p->pw_dir, p->pw_shell);endpwent();return 0;If you don’t understand C, don’t worry about it. The output from pwcat is the userdatabase, in the traditional ‘/etc/passwd’ format of colon-separated fields. The fields are:Login nameThe user’s login name.Encrypted passwordUser-IDGroup-IDFull nameHome directoryThe user’s encrypted password. This may not be availableon some systems.The user’s numeric user ID number.The user’s numeric group ID number.The user’s full name, and perhaps other informationassociated with the user.The user’s login (or “home”) directory (familiar toshell programmers as $HOME).Login shellThe program that is run when the user logs in. Thisis usually a shell, such as bash.A few lines representative of pwcat’s output are as follows:$ pwcat⊣ root:3Ov02d5VaUPB6:0:1:Operator:/:/bin/sh⊣ nobody:*:65534:65534::/:⊣ daemon:*:1:1::/:⊣ sys:*:2:2::/:/bin/csh⊣ bin:*:3:3::/bin:⊣ arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/sh⊣ miriam:yxaay:112:10:Miriam Robbins:/home/miriam:/bin/sh⊣ andy:abcca2:113:10:Andy Jacobs:/home/andy:/bin/sh...
Page 1 and 2:
GAWK: Effective AWK ProgrammingA Us
Page 3:
To Miriam, for making me complete.T
Page 6 and 7:
iiGAWK: Effective AWK ProgrammingTa
Page 8 and 9:
ivGAWK: Effective AWK Programming5
Page 10 and 11:
viGAWK: Effective AWK Programming10
Page 12 and 13:
viiiGAWK: Effective AWK Programming
Page 14 and 15:
2 GAWK: Effective AWK Programmingea
Page 16 and 17:
4 GAWK: Effective AWK ProgrammingAf
Page 18 and 19:
6 GAWK: Effective AWK ProgrammingCh
Page 20 and 21:
8 GAWK: Effective AWK ProgrammingGN
Page 22 and 23:
10 GAWK: Effective AWK Programmingt
Page 24 and 25:
12 GAWK: Effective AWK ProgrammingT
Page 26 and 27:
14 GAWK: Effective AWK Programmingp
Page 28 and 29:
16 GAWK: Effective AWK Programming$
Page 30 and 31:
Page 32 and 33:
20 GAWK: Effective AWK Programming
Page 34 and 35:
22 GAWK: Effective AWK ProgrammingH
Page 36 and 37:
24 GAWK: Effective AWK Programming2
Page 38 and 39:
26 GAWK: Effective AWK Programming\
Page 40 and 41:
28 GAWK: Effective AWK Programming[
Page 42 and 43:
30 GAWK: Effective AWK Programmings
Page 44 and 45:
Page 46 and 47:
Page 48 and 49:
Page 50 and 51:
Page 52 and 53:
40 GAWK: Effective AWK Programming$
Page 54 and 55:
42 GAWK: Effective AWK Programmingh
Page 56 and 57:
Page 58 and 59:
46 GAWK: Effective AWK ProgrammingB
Page 60 and 61:
Page 62 and 63:
Page 64 and 65:
Page 66 and 67:
54 GAWK: Effective AWK Programming{
Page 68 and 69:
Page 70 and 71:
Page 72 and 73:
Page 74 and 75:
62 GAWK: Effective AWK Programming%
Page 76 and 77:
Page 78 and 79:
66 GAWK: Effective AWK ProgrammingI
Page 80 and 81:
Page 82 and 83:
Page 84 and 85:
72 GAWK: Effective AWK ProgrammingS
Page 86 and 87:
74 GAWK: Effective AWK Programmingo
Page 88 and 89:
Page 90 and 91:
78 GAWK: Effective AWK Programmingh
Page 92 and 93:
80 GAWK: Effective AWK Programmingf
Page 94 and 95:
82 GAWK: Effective AWK Programmingx
Page 96 and 97:
Page 98 and 99:
86 GAWK: Effective AWK ProgrammingA
Page 100 and 101:
88 GAWK: Effective AWK ProgrammingU
Page 102 and 103:
90 GAWK: Effective AWK ProgrammingI
Page 104 and 105:
92 GAWK: Effective AWK ProgrammingS
Page 106 and 107:
94 GAWK: Effective AWK ProgrammingA
Page 108 and 109:
Page 110 and 111:
Page 112 and 113:
Page 114 and 115:
Page 116 and 117:
Page 118 and 119:
Page 120 and 121:
Page 122 and 123:
Page 124 and 125:
Page 126 and 127:
Page 128 and 129:
Page 130 and 131:
Page 132 and 133:
Page 134 and 135:
Page 136 and 137:
Page 138 and 139:
Page 140 and 141:
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
Page 150 and 151:
Page 152 and 153:
Page 154 and 155:
Page 156 and 157:
Page 158 and 159:
Page 160 and 161:
Page 162 and 163:
Page 164 and 165:
Page 166 and 167:
Page 168 and 169: 156 GAWK: Effective AWK Programming
Page 268 and 269:
Page 270 and 271:
Page 272 and 273:
Page 274 and 275:
Page 276 and 277:
Page 278 and 279:
Page 280 and 281:
Page 282 and 283:
Page 284 and 285:
Page 286 and 287:
Page 288 and 289:
Page 290 and 291:
Page 292 and 293:
Page 294 and 295:
Page 296 and 297:
Page 298 and 299:
Page 300 and 301:
Page 302 and 303:
Page 304 and 305:
Page 306 and 307:
Page 308 and 309:
Page 310 and 311:
Page 312 and 313:
Page 314 and 315:
Page 316 and 317:
Page 318 and 319:
Page 320 and 321:
Page 322 and 323:
Page 324 and 325:
Page 326 and 327:
Page 328 and 329:
Page 330 and 331:
Page 332 and 333:
Page 334 and 335:
Page 336 and 337:
Page 338 and 339:
Page 340 and 341:
Page 342 and 343:
Page 344 and 345:
Page 346 and 347:
Page 348 and 349:
Page 350 and 351:
Page 352 and 353:
Page 354 and 355:
Page 356 and 357:
Page 358 and 359:
Page 360 and 361:
Page 362 and 363:
Page 364:
show all

GAWK: Effective AWK Programming

Create successful ePaper yourself

Delete template?

Save as template?