GSP
Quick Navigator

Search Site

Unix VPS
A - Starter
B - Basic
C - Preferred
D - Commercial
MPS - Dedicated
Previous VPSs
* Sign Up! *

Support
Contact Us
Online Help
Handbooks
Domain Status
Man Pages

FAQ
Virtual Servers
Pricing
Billing
Technical

Network
Facilities
Connectivity
Topology Map

Miscellaneous
Server Agreement
Year 2038
Credits
 

USA Flag

 

 

Man Pages


Manual Reference Pages  -  PUTENV (3)

NAME

getenv, putenv, setenv, unsetenv - environment variable functions

CONTENTS

Library
Synopsis
Description
Return Values
Errors
See Also
Standards
History
Bugs

LIBRARY


.Lb libc

SYNOPSIS


.In 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, name. The application should not modify the string pointed to by the getenv function.

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 puts it directly into the current environment, so altering the argument shall change the environment. If the variable name does not exist in the list, it is inserted with the given value. If the variable name does exist, it is reset to the given value.

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

If corruption (e.g., a name without a value) is detected while making a copy of environ for internal usage, then setenv, unsetenv and putenv will output a warning to stderr about the issue, drop the corrupt entry and complete the task without error.

RETURN VALUES

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


.Rv -std setenv putenv unsetenv

ERRORS

[EINVAL]
  The function getenv, setenv or unsetenv failed because the name is a NULL pointer, points to an empty string, or points to a string containing an "=" character.

The function putenv failed because string is a NULL pointer, string is without an "=" character or "=" is the first character in string. This does not follow the POSIX specification.

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

SEE ALSO

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

STANDARDS

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

HISTORY

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

Until
.Fx 7.0 , putenv would make a copy of string and insert it into the environment using setenv. This was changed to use 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 value than any previous value to the same name will result in a memory leak. The
.Fx semantics for this function (namely, that the contents of 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.
Search for    or go to Top of page |  Section 3 |  Main Index


Powered by GSP Visit the GSP FreeBSD Man Page Interface.
Output converted with manServer 1.07.