putenv(3) - NetBSD Manual Pages

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GETENV(3)               NetBSD Library Functions Manual              GETENV(3)


NAME

     getenv, getenv_r, putenv, setenv, unsetenv -- environment variable func-
     tions


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <stdlib.h>

     char *
     getenv(const char *name);

     int
     getenv_r(const char *name, char *buf, size_t len);

     int
     setenv(const char *name, const char *value, int overwrite);

     int
     putenv(char *string);

     int
     unsetenv(const char *name);


DESCRIPTION

     These functions set, unset and fetch environment variables from the host
     environment list.  For compatibility with differing environment conven-
     tions, the getenv() or getenv_r() given argument name may be appended
     with an equal sign ``=''.

     The getenv() function obtains the current value of the environment vari-
     able name.  If the variable name is not in the current environment, a
     NULL pointer is returned.

     The getenv_r() function obtains the current value of the environment
     variable name and copies it to buf.  If name is not in the current envi-
     ronment, or the string length of the value of name is longer than len
     characters, then -1 is returned and errno is set to indicate the error.

     The setenv() function inserts or resets the environment variable name in
     the current environment list.  If the variable name does not exist in the
     list, it is inserted with the given value.  If the variable does exist,
     the argument overwrite is tested; if overwrite is zero, the variable is
     not reset, otherwise it is reset to the given value.

     The putenv() function takes an argument of the form ``name=value'' and it
     will set the environment variable ``name'' equal to ``value'' by altering
     an existing entry, or creating a new one if an existing one does not
     exist.  The actual string argument passed to putenv() will become part of
     the environment.  If one changes the string, the environment will also
     change.

     The unsetenv() function deletes all instances of the variable name
     pointed to by name from the list.


RETURN VALUES

     The functions getenv_r(), setenv(), putenv(), and unsetenv() return zero
     if successful; otherwise the global variable errno is set to indicate the
     error and a -1 is returned.

     If getenv() is successful, the string returned should be considered read-
     only.


ERRORS

     [EINVAL]           The name argument to setenv() or unsetenv() is a null
                        pointer, points to an empty string, or points to a
                        string containing an ``='' character.  The value argu-
                        ment to setenv() is a null pointer.  The string argu-
                        ment to putenv() is a null pointer, or points to a
                        string that either starts with a ``='' character or
                        does not contain one at all.

     [ENOMEM]           The function setenv() or putenv() failed because they
                        were unable to allocate memory for the environment.

     The function getenv_r() can return the following errors:

     [ENOENT]           The variable name was not found in the environment.

     [ERANGE]           The value of the named variable is too long to fit in
                        the supplied buffer.


SEE ALSO

     csh(1), sh(1), execve(2), environ(7)


STANDARDS

     The getenv() function conforms to ANSI X3.159-1989 (``ANSI C89'').  The
     putenv() function conforms to X/Open Portability Guide Issue 4
     (``XPG4'').  The unsetenv() function conforms to IEEE Std 1003.1-2001
     (``POSIX.1'').


HISTORY

     The functions setenv() and unsetenv() appeared in Version 7 AT&T UNIX.
     The putenv() function appeared in 4.3BSD-Reno.

NetBSD 8.2                     October 25, 2010                     NetBSD 8.2