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SETENV(3) Linux Programmer's Manual SETENV(3)


     setenv - change or add an environment variable


     #include <stdlib.h>
     int setenv(const char *name, const char *value, int overwrite);
     int unsetenv(const char *name);
 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
     setenv(), unsetenv():
         _POSIX_C_SOURCE >= 200112L
             || /* Glibc versions <= 2.19: */ _BSD_SOURCE


     The  setenv()  function  adds the variable name to the environment with
     the value value, if name does not already exist.  If name does exist in
     the  environment,  then  its  value is changed to value if overwrite is
     nonzero; if overwrite is zero, then the value of name  is  not  changed
     (and setenv() returns a success status).  This function makes copies of
     the strings pointed to by name and value (by contrast with  putenv(3)).
     The unsetenv() function deletes the variable name from the environment.
     If name does not exist in the environment, then the function  succeeds,
     and the environment is unchanged.


     The  setenv()  function  returns  zero on success, or -1 on error, with
     errno set to indicate the cause of the error.
     The unsetenv() function returns zero on success, or -1 on  error,  with
     errno set to indicate the cause of the error.


     EINVAL name is NULL, points to a string of length 0, or contains an '='
     ENOMEM Insufficient memory to add a new variable to the environment.


     For  an  explanation  of  the  terms  used   in   this   section,   see
     allbox; lb lb lb l l l.  Interface Attribute Value T{ setenv(),
     unsetenv() T}   Thread safety  MT-Unsafe const:env


     POSIX.1-2001, POSIX.1-2008, 4.3BSD.


     POSIX.1 does not require setenv() or unsetenv() to be reentrant.
     Prior to glibc 2.2.2, unsetenv() was prototyped as returning void; more
     recent  glibc  versions follow the POSIX.1-compliant prototype shown in
     the SYNOPSIS.


     POSIX.1 specifies that if name contains an '=' character, then setenv()
     should  fail  with  the error EINVAL; however, versions of glibc before
     2.3.4 allowed an '=' sign in name.


     clearenv(3), getenv(3), putenv(3), environ(7)


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     description  of  the project, information about reporting bugs, and the
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GNU 2017-09-15 SETENV(3)

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