September 25, 2005 GETENV 3

### NAME

getenv, getenv_r, putenv, setenv, unsetenv - environment variable functions

### LIBRARY

Standard C Library (libc, -lc)

### SYNOPSIS

```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(```const 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 conventions, the given arguments name and value may be appended and prepended, respectively, with an equal sign `````=`'', except for unsetenv(``).

The getenv(``) function obtains the current value of the environment variable 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 environment, 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 is equivalent to:

  `

      setenv(name, value, 1);

  `

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 unsetenv(``) is a null pointer, points to an empty string, or points to a string containing an `````=`'' character.

[```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 4.3BSDReno.