gno/usr.man/man7/environ.7

.\" This man page has been written to conform with the lenviron v1.1.3
.\" release for Gno v2.0.3 and later by Devin Reade.  glyn@cs.ualberta.ca
.\"
.TH ENVIRON 7 "15 April 1998" GNO "Miscellaneous"
.SH NAME
environ \- user environment
.SH SYNOPSIS
#include <stdlib.h>
.LP
.B "extern char **environ;"
.SH DESCRIPTION
Under UNIX, an array of strings called the `environment' is made available by
.BR execve (2)
when a process begins.  By convention these strings have the
form \fIname=value\fR.
However, because of the shell variable and environment passing mechanisms
normally provided for the IIgs (and with GNO and ORCA in particular), this
method of controlling and accessing the environment has not previously been
available.  Specifically, under GNO and ORCA
.BR environ
is not initialized by the
.BR exec (3)
family of calls.  To accomodate this \'feature\', the library call
.BR environInit (3)
has been provided to properly initialize
.BR environ .
.LP
The following names are used by various commands:
.RS
.IP \fBPATH\fR
The sequence of directory prefixes that
.BR gsh (1),
.BR sh (1),
.BR time (1V),
.BR nice (1),
etc., apply in searching for a file known by an incomplete path name.
The prefixes are delimited by spaces since colons are valid pathname
characters under GS/OS.  Current versions of
.B gsh
parse
.B PATH
backwards, that is from back to front.
.B lenviron
has been compiled to match this behavior, but can be easily recompiled
to conform to the more usual parsing method, front to back.  See the
.B lenviron
distribution README file for more information.
.IP \fBHOME\fR
The name of the user's login directory, set by
.BR login (1)
from the password file
.B /etc/passwd
(see
.BR passwd (5)).
.IP \fBTERM\fR
The type of terminal on which the user is logged in.
This information is used by commands, such as
.BR nroff (1)
or
.BR plot (1G),
which may exploit special terminal capabilities.  See
.B /etc/termcap
.RB ( termcap (5))
for a list of terminal types.
.IP \fBSHELL\fR
The path name of the user's login shell.
.IP \fBTERMCAP\fR
The string describing the terminal in
.SM TERM,
or the name of the
.B termcap
file, see
.BR termcap (3),
.BR termcap (5).
.IP \fBEXINIT\fR
A startup list of commands read by
.BR ex (1),
.BR edit ,
and
.BR vi (1).
.IP "\fBUSER\fR or \fBLOGNAME\fR"
The user's login name.
.IP \fBTZ\fR
The name of the time zone that the user is located in.  If
.B TZ
is not present in the environment, the system's default time zone,
normally the time zone that the computer is located in, is used.
.RE
.LP
Further names may be placed in the environment by the
.IR set " and " setenv
commands under
.BR gsh (1),
the
.I export
command and
.IR name = value
arguments in
.BR sh (1),
or by the
.B setenv
command if you use
.BR csh (1).
It is unwise to conflict with certain
.BR sh (1)
variables that are frequently exported by
.B .profile
files:
.BR \s-1MAIL\s0 ,
.BR \s-1PS\s01 ,
.BR \s-1PS\s02 ,
.BR \s-1IFS\s0 .
.LP
Various names are expected to be defined and used by
locale dependent commands and functions
(see
.BR locale (5)).
.SH GNO IMPLEMENTATION
The GNO implementation of the environment actually has two sets of shell
variables.  The first is the NULL\-terminated array of strings pointed to by
.BR environ .
The second is the set of internal shell variables set by such system calls as
.BR SetGS " and " UnsetVariableGS .
The latter of these is the one normally used by ORCA/C.  Unfortunately, the
latter implementation makes the porting of some UNIX utilities more
difficult.  The
.BR environ
library was created to solve this problem without adding significant overhead
to environment calls when reference to
.BR environ
is not needed.
.LP
When the
.BR environ
variable is not needed, calls made to
.BR putenv (3),
.BR setenv "(3), and"
.BR getenv (3)
result in only the internal shell variables to be set, and
.BR environ
will remain NULL; its default value.
.LP
If, however,
.BR environ
is to be accessed, then an initial call must be made to
.BR environInit (3).
This produces the array of strings based on the shell variables defined
internally, and keeps the array current with further calls to
.BR putenv "(3), or"
.BR setenv (3).
.SH CAVEATS                                                  
Under the ORCA shell, three `extraneous' shell variables are defined:
.BR STATUS ,
.BR Command ", and"
.BR Exit .
These are reset with every call to the ORCA shell and should not, in general,
be considered to be current.
.LP
When one of the
.BR exec (3)
family of calls is carried out, the environment will not be passed on through
.BR environ .
In order for the next process to use
.BR environ ,
it must make another call to
.BR environInit (3).
Note, however, that child processes will still have residing in the internal
shell variables all previous modifications to the environment.
.LP
In order to conduct an environment context switch, you must invoke the functions
.BR environPush (3)
and
.BR environPop (3).
This context switch behaves similarily to
.BR PushVariableGS " or " PopVariableGS ,
but will result in both internal and external shell variables being saved
and restored, rather than just the internal variables.
.LP
While the
.BR environ
array may be read by user applications, it cannot be directly modified with
impudence; any additions or deletions to the
.BR environ
array other that through the mentioned routines will not be reflected in the
internal shell variables. Also, since environ entries are dynamically
allocated and freed, modifying those entries without using the library
routines may result in memory trashing and unpredicable behavior.
.SH FILES                                 
/etc/passwd
.br
/etc/termcap
.SH HISTORY
This
.BR environ
implementation was first made available in the (now deprecated) 
.IR lenviron
library.  It was incorporated into 
.IR libc
as of GNO v2.0.6.
.SH AUTHORS
The original environ library (and consequently portions of the current
libc) was created for GNO and ORCA/Shell by Devin Reade.  This implementation
also contains code fragments from Dave Tribby and James Brookes.
.LP
The environ library also contains code is derived from software contributed
to Berkeley by the American National Standards Committee X3, on
Information Processing Systems.  Those portions are copyright (c) 1988,
1991.  The Regents of the University of California.  All rights reserved.
.SH SEE ALSO
.BR gsh (1),
.BR execve (2),
.BR exec (3),
.BR execl (3),
.BR getenv (3),
.BR system (3),
.BR termcap (3),
.BR passwd (5),
.BR termcap (5)