1PUTENV(3) Linux Programmer's Manual PUTENV(3)
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6 putenv - change or add an environment variable
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9 #include <stdlib.h>
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11 int putenv(char *string);
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13 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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15 putenv():
16 _XOPEN_SOURCE
17 || /* Glibc since 2.19: */ _DEFAULT_SOURCE
18 || /* Glibc <= 2.19: */ _SVID_SOURCE
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21 The putenv() function adds or changes the value of environment vari‐
22 ables. The argument string is of the form name=value. If name does
23 not already exist in the environment, then string is added to the envi‐
24 ronment. If name does exist, then the value of name in the environment
25 is changed to value. The string pointed to by string becomes part of
26 the environment, so altering the string changes the environment.
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29 The putenv() function returns zero on success. On failure, it returns
30 a nonzero value, and errno is set to indicate the error.
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33 ENOMEM Insufficient space to allocate new environment.
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36 For an explanation of the terms used in this section, see at‐
37 tributes(7).
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39 ┌────────────────────────────────┬───────────────┬─────────────────────┐
40 │Interface │ Attribute │ Value │
41 ├────────────────────────────────┼───────────────┼─────────────────────┤
42 │putenv() │ Thread safety │ MT-Unsafe const:env │
43 └────────────────────────────────┴───────────────┴─────────────────────┘
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46 POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
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49 The putenv() function is not required to be reentrant, and the one in
50 glibc 2.0 is not, but the glibc 2.1 version is.
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52 Since version 2.1.2, the glibc implementation conforms to SUSv2: the
53 pointer string given to putenv() is used. In particular, this string
54 becomes part of the environment; changing it later will change the en‐
55 vironment. (Thus, it is an error to call putenv() with an automatic
56 variable as the argument, then return from the calling function while
57 string is still part of the environment.) However, glibc versions 2.0
58 to 2.1.1 differ: a copy of the string is used. On the one hand this
59 causes a memory leak, and on the other hand it violates SUSv2.
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61 The 4.4BSD version, like glibc 2.0, uses a copy.
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63 SUSv2 removes the const from the prototype, and so does glibc 2.1.3.
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65 The GNU C library implementation provides a nonstandard extension. If
66 string does not include an equal sign:
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68 putenv("NAME");
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70 then the named variable is removed from the caller's environment.
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73 clearenv(3), getenv(3), setenv(3), unsetenv(3), environ(7)
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76 This page is part of release 5.13 of the Linux man-pages project. A
77 description of the project, information about reporting bugs, and the
78 latest version of this page, can be found at
79 https://www.kernel.org/doc/man-pages/.
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83GNU 2021-03-22 PUTENV(3)