10-20-2010
Quote:
Originally Posted by
methyl
This is not strictly true.
Those environment variables are set by the program "login". See "man login". The program "login" executes before Shell starts. However not every Shell starts from "login".
It is quite possible to start a Shell without anything setting $HOME $PATH etc..
There are also differences in "csh".
The when you run in other milieu, such as "rsh/ssh/ssh2 host command", the environment may be even less. That is where 'set' is so nice: try it and see. Your cron may vary.
Especially if you write commands for set-uid or set-groupid, the environment is removed and shell scripts generally need not apply, just C and the like compiled with -R for trustworthy, hard-wired library search path to foil hackers.
10 More Discussions You Might Find Interesting
1. UNIX for Dummies Questions & Answers
what is the actual use of environment variables.
I know only PS1, LOGNAME, PS2 variables
what are the other variables & what is there use (2 Replies)
Discussion started by: indianguru
2 Replies
2. Programming
Hi!
How-to get the environment variables in GNU.
getenv() only fetches the ones that you can find under export (not the ones under declare)...
best regars .David (2 Replies)
Discussion started by: Esaia
2 Replies
3. UNIX for Dummies Questions & Answers
Hi Folks,
Is it possible somehow to unset all the environment variables which have been defined before in UNIX (Solaris).
Thanks,
Slava (3 Replies)
Discussion started by: spavlov
3 Replies
4. UNIX for Dummies Questions & Answers
hi,
1). i would like to know what is meant by environment variables?
2). is the number of envi variables is a constant number for unix systems?
3). how to see the list of envi variables (and the values of the envi variables)in a single command?
4). if this questions were already asked... (3 Replies)
Discussion started by: sekar sundaram
3 Replies
5. Programming
hi,
I want to create a new EV(Environment Variable) through a c program and I done this thing through setenv() method. But the newly created EV is not permanent, i.e. when I exit from the program the EV also no longer lives. But I want to make it a permanent EV for the current user. Actually I... (6 Replies)
Discussion started by: sumsin
6 Replies
6. Shell Programming and Scripting
Hi,
If i have a variable set and exported in my pofile file will that variable be available in all shell scripts created.
Thanks,
Radhika. (3 Replies)
Discussion started by: radhika03
3 Replies
7. Shell Programming and Scripting
I have read tons of posts about how you can't set persisting environment variable in a child script of a shell and have it persist. The only way is to source a file as
% . <scriptname>
I am finding that true... but I know there is a way around it. I just don't know how. I worked for 6... (5 Replies)
Discussion started by: rwa25
5 Replies
8. HP-UX
Hi Experts,
Need your help in understanding the commands to setup the environment variables in hp-ux.
Beleive need to use either set,setenv or export.
I am confused between above three options, when to use which option?
On command line, I have tried both set and setenv but couldn't... (1 Reply)
Discussion started by: sai_2507
1 Replies
9. Homework & Coursework Questions
1. The problem statement:
What is the mesg value set for your environment? If it is on, how would you turn off your current
session? How would you set it permanently?
3. The attempts at a solution :
Read Unix The textbook.
3rd chapter has many things like environment variables and... (5 Replies)
Discussion started by: mahinkhan22
5 Replies
10. HP-UX
Hi All,
I need to understand following three environment variables and their usages in HP Unix.
_M_ARENA_OPTS
_M_CACHE_OPTS
PTHREAD_SCOPE_SYSTEM
How does these environment variables influence multi threaded applciation and how do we decide the value of these variables? Is there... (0 Replies)
Discussion started by: angshuman
0 Replies
LEARN ABOUT OPENDARWIN
su
SU(1) BSD General Commands Manual SU(1)
NAME
su -- substitute user identity
SYNOPSIS
su [-flm] [login] [-c shell arguments]
DESCRIPTION
su requests the password for login and switches to that user and group ID after obtaining proper authentication. A shell is then executed,
and any additional shell arguments after the login name are passed to the shell. If su is executed by root, no password is requested and a
shell with the appropriate user ID is executed.
The options are as follows:
-c Invoke the following command in a subshell as the specified user.
-f If the invoked shell is csh(1), this option prevents it from reading the ``.cshrc'' file.
-l Simulate a full login. The environment is discarded except for HOME, SHELL, PATH, TERM, and USER. HOME and SHELL are modified as
above. USER is set to the target login. PATH is set to ``/bin:/usr/bin''. TERM is imported from your current environment. The
invoked shell is the target login's, and su will change directory to the target login's home directory. This option is identical to
just passing "-", as in "su -".
-m Leave the environment unmodified. The invoked shell is your login shell, and no directory changes are made. As a security precau-
tion, if the target user's shell is a non-standard shell (as defined by getusershell(3)) and the caller's real uid is non-zero, su
will fail.
The -l and -m options are mutually exclusive; the last one specified overrides any previous ones.
Only users in group ``wheel'' (normally gid 0) or group ``admin'' (normally gid 20) can su to ``root''.
By default (unless the prompt is reset by a startup file) the super-user prompt is set to ``#'' to remind one of its awesome power.
SEE ALSO
csh(1), login(1), sh(1), skey(1), kinit(1), kerberos(1), passwd(5), group(5), environ(7)
ENVIRONMENT
Environment variables used by su :
HOME Default home directory of real user ID unless modified as specified above.
PATH Default search path of real user ID unless modified as specified above.
TERM Provides terminal type which may be retained for the substituted user ID.
USER The user ID is always the effective ID (the target user ID) after an su unless the user ID is 0 (root).
HISTORY
A su command appeared in Version 7 AT&T UNIX.
BSD
April 18, 1994 BSD