getenv.3

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 3 代码 · 共 61 行

.\" SCCSID: @(#)getenv.3	8.1	9/11/90
.TH getenv 3
.SH Name
getenv, setenv, unsetenv  \- manipulate environment variables
.SH Syntax
.nf
.B char *getenv(\fIname\fP)
.B char *\fIname\fP;
.PP
.B setenv(\fIname\fP, \fIvalue\fP, \fIoverwrite\fP)
.B char *\fIname\fP, \fIvalue\fP;
.B int \fIoverwrite\fP;
.PP
.B void unsetenv(\fIname\fP)
.B char *\fIname\fP;
.fi
.SH Description
.NXR "getenv subroutine (standard C)"
.NXR "environment" "getting variable values"
The
.PN getenv
subroutine searches the environment list
for a string of the form
.I name = value
and returns a pointer to the string
.I value
if such a string is present, otherwise 
.PN getenv
returns the value 0 (NULL).
For further information, see 
.MS environ 7 .
.PP
The 
.PN setenv 
subroutine searches the environment list in the same manner as 
.PN getenv. 
If the string \fIname\fP is not found, a string of the form
\fIname\fP=\fIvalue\fP is added to the environment.  If it is
found, and \fIoverwrite\fP is non-zero, its value is changed to
\fIvalue\fP.  The
.PN setenv 
subroutine returns 0 on success and \-1 on failure,
where failure is caused by an inability to allocate space for the
environment.
.PP
The 
.PN unsetenv 
subroutine removes all occurrences of the string \fIname\fP from
the environment.  There is no library provision for completely removing
the current environment.  It is suggested that the following code be
used to do so.
.EX
static char     *envinit[1];
extern char     **environ;
environ = envinit;
.EE
All of these routines permit, but do not require, a trailing equals
sign (=) on \fIname\fP or a leading equals sign on \fIvalue\fP.
.SH See Also
 csh(1), sh(1), execve(2), putenv(3), environ(7)