POSIX programmer's guide: writing portable UNIX programs with the POSIX.1 standard

574 Pages·1991·2.606 MB·English

by  Donald Lewine

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POSIX Programmer's Guide
Writing Portable UNIX Programs with the POSIX.1 Standard
Donald A. Lewine
Data General Corporation
O'Reilly & Associates, Inc
103 Morris Street, Suite A
Sebastopol, CA 95472
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POSIX Programmer's Guide
by Donald A. Lewine
Editor: Dale Dougherty
Copyright © 1991 O'Reilly & Associates, Inc.
All rights reserved
Printed in the United States of America
Printing History
April 1991: First edition
December 1991: Minor corrections. Appendix G added.
July 1992: Minor corrections.
November 1992: Minor corrections.
March 1994: Minor corrections and updates.
NOTICE
Portions of this text have been reprinted from IEEE Std 1003.1-1988, IEEE Standard Portable
Operating System for Computer Environments, copyright © 1988 by the Institute of Electrical
and Electronics Engineers, Inc., and IEEE Std 1003.1-1990, Information
Technology—Portable Operating System Interface (POSIX)—Part 1: System Application
Program Interface (API) [C Language], copyright © 1990 by the Institute of Electrical and
Electronics Engineers, Inc., with the permission of the IEEE Standards Department.
Nutshell Handbook and the Nutshell Handbook logo are registered trademarks of O'Reilly &
Associates, Inc. Many of the designations used by manufacturers and sellers to distinguish their
products are claimed as trademarks. Where those designations appear in this book, and
O'Reilly and Associates, Inc. was aware of a trademark claim, the designations have been
printed in caps or initial caps.
While every precaution has been taken in the preparation of this book, the publisher assumes no
responsibility for errors or omissions, or for damages resulting from the use of the information
contained herein.
Please address comments and questions in care of the publisher:
O'Reilly & Associates, Inc. INTERNET: [email protected]
103 Morris Street, Suite A
Sebastopol, CA 9547
[phone]
[8/98] ISBN: 0-937175-73-0
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To all my students
To my wife, Susan,
who convinced me to do this
book and who put up with
all the time this effort took
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Acknowledgments
I would like to thank all of my students who put up with all of the beta test quality revisions.
They provided many useful suggestions.
I would like to thank some people who provided very complete technical reviews and
provided useful comments: Hal Jespersen (Posix Software Group), Chuck Karish (Mindcraft,
Inc.), Thomas Mitas (HBO & Company), Neil Todd (European UNIX Systems User Group),
Andy Huber (Data General Corporation), Richard Eckhouse (University of Massachusetts),
Andy Silverman (88open Consortium), Henry Spencer (University of Toronto), Jeffrey S.
Haemer (Interactive Systems Corporation), Paul Rabin, Dave Kirschen, and Michael Meissner
(Open Software Foundation), and John S. Quarterman (Texas Internet Consulting).
Thanks go to the following readers of previous printings who pointed out errors and typos:
Eric Boweles, Eric Hanchrow, Milt Ratcliff, Stephen J. Friedl, Ed Myer, Chesley Reyburn.
Derek M. Jones, Todd Stevenson, Bob Burchfield, Anthony Scian, and Wayne Pallock
Thanks to Allen Gray for his help with the reference material. Thanks to Mike Sierra and Ellie
Cutler of O'Reilly & Associates for doing the production work and for writing the index.
Special thanks to Dale Dougherty for a great job of editing. His many useful suggestions were
worth the months they took to implement.
Thanks to the POSIX standards committees for making this book possible.
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Table of Contents
Preface xxiii
The POSIX Standard Documents xxiv
Guide to POSIX for Programmers xxv
Programming Guide xxv
Reference Guide and Appendixes xxvi
Assumptions xxvi
Conventions xxvii
Chapter 1 Introduction to POSIX and Portability 1
Who is Backing POSIX? 2
The POSIX Family of Standards 3
The POSIX.1 Standard Document 5
The Design of POSIX 7
POSIX and UNIX 7
7
POSIX and Non-UNIX Operating Systems 8
POSIX, C, ANSI C, and Standard C 8
Why Standard C? 9
Working Outside the Standards 10
Finding The POSIX Libraries 11
Converting Existing Programs 11
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Chapter 2 Developing POSIX Applications 13
The POSIX Development Environment 13
The Standard C Compiler 13
POSIX and C Libraries 14
Converting Existing Programs 15
A Porting Example 16
An Alternate Approach 19
Standard Header Files 20
Template for a POSIX Application 24
/* Feature test switches */ 25
/* System headers */ 25
/* Local headers */ 25
/* Macros */ 25
/* File scope variables */ 25
/* External variables */ 26
/* External functions */ 26
/* Structures and unions */ 26
/* Signal catching functions */ 26
26
/* Functions */ 26
/* Main */ 26
Sample Program 26
Portability Lab 38
Chapter 3 Standard File and Terminal I/O 39
Libraries and System Calls 39
Standard Files 39
Formatted Output 40
Examples 41
Pitfalls 42
The vfprintf(), vprintf(), and vsprintf() Functions 43
Character Output Functions 45
The fputs() and puts() Functions 45
The fputc(), putc(), and putchar() Functions 45
Reading Lines of Input 45
Pitfalls 47
Additional Pitfall 47
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Other Character Input Functions 47
The fgetc(), getc() and getchar() Functions 47
The fgets() Function 48
The gets() Function 48
The ungetc() Function 48
Opening and Closing Files 49
Direct Input/Output functions 50
50
The fwrite() and fread() Functions 50
File Positioning Functions 50
The fgetpos() and fsetpos() Functions 51
The ftell() and fseek() Function 51
The rewind() Function 51
Managing Buffers 52
Sample Program 53
Portability Lab 60
Chapter 4 Files and Directories 63
Portable Filenames 63
Directory Tree 64
Current Working Directory 64
Making and Removing Directories 66
The rmdir() Function 67
Simulating the mkdir() and rmdir() Functions 67
Directory Structure 67
Manipulating Directories 68
Linking to a File 69
Removing a File 69
Renaming a File 69
File Characteristics 69
Retrieving a File's Characteristics 72
Changing File Accessibility 73
Changing the Owner of a File 73
Setting File Access and Modification Times 74
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Reading Directories 75
The opendir() Function 76
The readdir() Function 76
The closedir() Function 76
The rewinddir() Function 76
General Comments 76
Complete Example 77
Pitfall: Symbolic Links 83
Portability Lab 84
Chapter 5 Advanced File Operations 85
Primitive File Operations 86
File Descriptors 87
Opening a file 87
Reading from a File 89
Writing to a File 89
Fast File Copy Example 90
Control Operations on a File 92
F_GETFD/F_SETFD 92
F_GETFL/F_SETFL 93
F_SETLK/F_SETLKW/F_GETLK 94
F_DUPFD 95
Setting the File Position 95
The dup() and dup2() Functions 96
Closing a File 96
FIFOs and Pipes 96
96
File Creation Mask 97
The umask() Function 98
Mixing the Levels 98
The fdopen() Function 98
The fileno() Function 98
Pitfalls 99
Portability Lab 99
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Chapter 6 Working with Processes 101
Process Creation 101
The fork() Function 101
The exec() Family of Function 102
Example: Piping Output Through more 103
Portability Note 105
Process Termination 106
The wait() and waitpid() Functions 106
Terminating the Current Process 108
Returning from main() 108
Calling exit() 109
Calling _exit() 109
Calling abort() 110
Terminating Another Process 110
Signals 110
Signal Actions 112
Signal-Catching Functions 112
112
Examine and Change Signal Action 113
Standard C Signals 113
POSIX Signals 114
Example: Timing a System Function 116
Signal Sets 117
The sigemptyset() Function 118
The sigfillset() Function 118
The sigaddset() Function 118
The sigdelset() Function 118
Using the sigset Functions 118
The sigismember() Function 119
The sigprocmask() Function 119
The sigpending() Function 119
Wait for a Signal 120
Sending a Signal 121
Portability Lab 122
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Chapter 7 Obtaining Information at Run-time 123
Process Identification 123
User Identification 123
User IDs 125
Group IDs 126
System Identification 132
Date and Time 133
The time() Function 133
133
The localtime() and gmtime() Functions 133
The mktime() Function 135
The strftime() Function 135
The asctime() and ctime() Functions 137
The difftime() Function 137
The clock() and times() Functions 137
Environment Variables 138
The getenv() Function 139
The sysconf() Function 140
The pathconf() and fpathconf() Functions 142
Portability Lab 143
Chapter 8 Terminal I/0 145
Terminal Concepts 146
Setting Terminal Parameters 147
The tcsetattr() and tcgetattr() Functions 147
The termios Structure 148
System V termio and POSIX termios Structures 149
Example: Reading a Password 150
Input Processing 152
Output Processing 152
Modem Control 153
Non-Canonical I/O 153
Input Modes 153
Output Modes 154
Control Modes 155
Local Modes 155