1CONFSTR(3P) POSIX Programmer's Manual CONFSTR(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
13 confstr — get configurable variables
14
16 #include <unistd.h>
17 size_t confstr(int name, char *buf, size_t len);
19
21 The confstr() function shall return configuration-defined string val‐
22 ues. Its use and purpose are similar to sysconf(), but it is used where
23 string values rather than numeric values are returned.
24 The name argument represents the system variable to be queried. The
26 implementation shall support the following name values, defined in
27 <unistd.h>. It may support others:
28 _CS_PATH
30 _CS_POSIX_V7_ILP32_OFF32_CFLAGS
31 _CS_POSIX_V7_ILP32_OFF32_LDFLAGS
32 _CS_POSIX_V7_ILP32_OFF32_LIBS
33 _CS_POSIX_V7_ILP32_OFFBIG_CFLAGS
34 _CS_POSIX_V7_ILP32_OFFBIG_LDFLAGS
35 _CS_POSIX_V7_ILP32_OFFBIG_LIBS
36 _CS_POSIX_V7_LP64_OFF64_CFLAGS
37 _CS_POSIX_V7_LP64_OFF64_LDFLAGS
38 _CS_POSIX_V7_LP64_OFF64_LIBS
39 _CS_POSIX_V7_LPBIG_OFFBIG_CFLAGS
40 _CS_POSIX_V7_LPBIG_OFFBIG_LDFLAGS
41 _CS_POSIX_V7_LPBIG_OFFBIG_LIBS
42 _CS_POSIX_V7_THREADS_CFLAGS
43 _CS_POSIX_V7_THREADS_LDFLAGS
44 _CS_POSIX_V7_WIDTH_RESTRICTED_ENVS
45 _CS_V7_ENV
46 _CS_POSIX_V6_ILP32_OFF32_CFLAGS
47 _CS_POSIX_V6_ILP32_OFF32_LDFLAGS
48 _CS_POSIX_V6_ILP32_OFF32_LIBS
49 _CS_POSIX_V6_ILP32_OFFBIG_CFLAGS
50 _CS_POSIX_V6_ILP32_OFFBIG_LDFLAGS
51 _CS_POSIX_V6_ILP32_OFFBIG_LIBS
52 _CS_POSIX_V6_LP64_OFF64_CFLAGS
53 _CS_POSIX_V6_LP64_OFF64_LDFLAGS
54 _CS_POSIX_V6_LP64_OFF64_LIBS
55 _CS_POSIX_V6_LPBIG_OFFBIG_CFLAGS
56 _CS_POSIX_V6_LPBIG_OFFBIG_LDFLAGS
57 _CS_POSIX_V6_LPBIG_OFFBIG_LIBS
58 _CS_POSIX_V6_WIDTH_RESTRICTED_ENVS
59 _CS_V6_ENV
60 If len is not 0, and if name has a configuration-defined value, conf‐
62 str() shall copy that value into the len-byte buffer pointed to by buf.
63 If the string to be returned is longer than len bytes, including the
64 terminating null, then confstr() shall truncate the string to len−1
65 bytes and null-terminate the result. The application can detect that
66 the string was truncated by comparing the value returned by confstr()
67 with len.
68 If len is 0 and buf is a null pointer, then confstr() shall still
70 return the integer value as defined below, but shall not return a
71 string. If len is 0 but buf is not a null pointer, the result is
72 unspecified.
73 After a call to:
75 confstr(_CS_V7_ENV, buf, sizeof(buf))
77 the string stored in buf will contain the <space>-separated list of
79 variable=value environment variable pairs required by the implementa‐
80 tion to create a conforming environment, as described in the implemen‐
81 tations' conformance documentation.
82 If the implementation supports the POSIX shell option, the string
84 stored in buf after a call to:
85 confstr(_CS_PATH, buf, sizeof(buf))
87 can be used as a value of the PATH environment variable that accesses
89 all of the standard utilities of POSIX.1‐2008, if the return value is
90 less than or equal to sizeof(buf).
91
93 If name has a configuration-defined value, confstr() shall return the
94 size of buffer that would be needed to hold the entire configuration-
95 defined value including the terminating null. If this return value is
96 greater than len, the string returned in buf is truncated.
97 If name is invalid, confstr() shall return 0 and set errno to indicate
99 the error.
100 If name does not have a configuration-defined value, confstr() shall
102 return 0 and leave errno unchanged.
103
105 The confstr() function shall fail if:
106 EINVAL The value of the name argument is invalid.
108 The following sections are informative.
110
112 None.
113
115 An application can distinguish between an invalid name parameter value
116 and one that corresponds to a configurable variable that has no config‐
117 uration-defined value by checking if errno is modified. This mirrors
118 the behavior of sysconf().
119 The original need for this function was to provide a way of finding the
121 configuration-defined default value for the environment variable PATH.
122 Since PATH can be modified by the user to include directories that
123 could contain utilities replacing the standard utilities in the Shell
124 and Utilities volume of POSIX.1‐2008, applications need a way to deter‐
125 mine the system-supplied PATH environment variable value that contains
126 the correct search path for the standard utilities.
127 An application could use:
129 confstr(name, (char *)NULL, (size_t)0)
131 to find out how big a buffer is needed for the string value; use mal‐
133 loc() to allocate a buffer to hold the string; and call confstr() again
134 to get the string. Alternately, it could allocate a fixed, static buf‐
135 fer that is big enough to hold most answers (perhaps 512 or 1024
136 bytes), but then use malloc() to allocate a larger buffer if it finds
137 that this is too small.
138
140 Application developers can normally determine any configuration vari‐
141 able by means of reading from the stream opened by a call to:
142 popen("command -p getconf variable", "r");
144 The confstr() function with a name argument of _CS_PATH returns a
146 string that can be used as a PATH environment variable setting that
147 will reference the standard shell and utilities as described in the
148 Shell and Utilities volume of POSIX.1‐2008.
149 The confstr() function copies the returned string into a buffer sup‐
151 plied by the application instead of returning a pointer to a string.
152 This allows a cleaner function in some implementations (such as those
153 with lightweight threads) and resolves questions about when the appli‐
154 cation must copy the string returned.
155
157 None.
158
160 exec, fpathconf(), sysconf()
161 The Base Definitions volume of POSIX.1‐2008, <unistd.h>
163 The Shell and Utilities volume of POSIX.1‐2008, c99
165
167 Portions of this text are reprinted and reproduced in electronic form
168 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
169 -- Portable Operating System Interface (POSIX), The Open Group Base
170 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
171 cal and Electronics Engineers, Inc and The Open Group. (This is
172 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
173 event of any discrepancy between this version and the original IEEE and
174 The Open Group Standard, the original IEEE and The Open Group Standard
175 is the referee document. The original Standard can be obtained online
176 at http://www.unix.org/online.html .
177 Any typographical or formatting errors that appear in this page are
179 most likely to have been introduced during the conversion of the source
180 files to man page format. To report such errors, see https://www.ker‐
181 nel.org/doc/man-pages/reporting_bugs.html .
182IEEE/The Open Group 2013 CONFSTR(3P)