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unsetenv (3)
  • unsetenv (1) ( Solaris man: Команды и прикладные программы пользовательского уровня )
  • unsetenv (1) ( FreeBSD man: Команды и прикладные программы пользовательского уровня )
  • unsetenv (3) ( Solaris man: Библиотечные вызовы )
  • >> unsetenv (3) ( FreeBSD man: Библиотечные вызовы )
  • unsetenv (3) ( Русские man: Библиотечные вызовы )
  • unsetenv (3) ( Linux man: Библиотечные вызовы )
  • unsetenv (3) ( POSIX man: Библиотечные вызовы )

  • BSD mandoc
     

    NAME

    
    
    getenv
    
     
    putenv
    
     
    setenv
    
     
    unsetenv
    
     - environment variable functions
    
     
    

    LIBRARY

    Lb libc
    
     
    

    SYNOPSIS

       #include <stdlib.h>
    char * getenv (const char *name);
    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

    The getenv ();
    function obtains the current value of the environment variable, Fa name . The application should not modify the string pointed to by the getenv ();
    function.

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

    The putenv ();
    function takes an argument of the form ``name=value'' and puts it directly into the current environment, so altering the argument shall change the environment. If the variable Fa name does not exist in the list, it is inserted with the given Fa value . If the variable Fa name does exist, it is reset to the given Fa value .

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

    RETURN VALUES

    The getenv ();
    function returns the value of the environment variable as a NUL -terminated string. If the variable Fa name is not in the current environment, NULL is returned.

    Rv -std setenv putenv unsetenv  

    ERRORS

    Bq Er EINVAL
    The function getenv (,);
    setenv ();
    or unsetenv ();
    failed because the Fa name is a NULL pointer, points to an empty string, or points to a string containing an ``= '' character.

    The function putenv ();
    failed because Fa string is a NULL pointer, Fa string is without an ``= '' character or ``= '' is the first character in Fa string . This does not follow the POSIX specification.

    Bq Er ENOMEM
    The function setenv (,);
    unsetenv ();
    or putenv ();
    failed because they were unable to allocate memory for the environment.
    Bq Er EFAULT
    The functions setenv (,);
    unsetenv ();
    or putenv ();
    failed to make a valid copy of the environment due to the environment being corrupt (i.e., a name without a value). A warning will be output to stderr with information about the issue.

     

    SEE ALSO

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

    STANDARDS

    The getenv ();
    function conforms to St -isoC . The setenv (,);
    putenv ();
    and unsetenv ();
    functions conforms to St -p1003.1-2001 .  

    HISTORY

    The functions setenv ();
    and unsetenv ();
    appeared in AT&T System v7 . The putenv ();
    function appeared in BSD 4.3 Reno

    Until Fx 7.0 , putenv ();
    would make a copy of Fa string and insert it into the environment using setenv (.);
    This was changed to use Fa string as the memory location of the ``name=value'' pair to follow the POSIX specification.  

    BUGS

    Successive calls to setenv ();
    that assign a larger-sized Fa value than any previous value to the same Fa name will result in a memory leak. The Fx semantics for this function (namely, that the contents of Fa value are copied and that old values remain accessible indefinitely) make this bug unavoidable. Future versions may eliminate one or both of these semantic guarantees in order to fix the bug.


     

    Index

    NAME
    LIBRARY
    SYNOPSIS
    DESCRIPTION
    RETURN VALUES
    ERRORS
    SEE ALSO
    STANDARDS
    HISTORY
    BUGS


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