Very Computer

I am still very new to scripting in Unix and hope you will help me a bit.
Here are a couple of examples of my troubles.

-------------------------------------------------
How do I check a username (or uid). I have tried man getuid, man uid etc.
and nothing comes up. Here is what I am trying to do:

if [ "${User}" != "root" ]; then
# Only su may run this script
    echo " Im sorry, but you may not use this script"
    exit 1
else
    continue
fi
--------------------------------------------------

Here is another test problem.

until [ "${test}" = 1 ]
# testvar is made to authenticate correct keystroke
do

echo " ---------------------------------------"
echo " -       Menusomething                         -"
echo " - Hit (U)ser, (G)roup or (D)isconnect -"
echo " ---------------------------------------"

read menu
if [ "${menu} = "u-U" ]; then
# should I use case instead? and what syntax makes u the same as U?
test=1
adduser;
# calls preveously defined function
elif [ "${menu} = "g-G" ]; then
test =1
addgr;
elif [ "${menu} = "d-D" ]; then
exit 0
else
echo "you mistyped"
echo
fi
done

echo "You made it through the Until sentence"
-----------------------------------------------------

  I have several other questions to making my little program work. But I
quess it's better to ask a little at a time.

regards from

Leif

PS: Thanks for helping me earlier. Scripting is a lot easyer than making C
programs.
Being not very educated I learn easyer by example (stealing or recycling)
and links to already made scripts will be most welcome

if [ "`whoami`" != root ]; then

Quote:>--------------------------------------------------

>Here is another test problem.

>until [ "${test}" = 1 ]
># testvar is made to authenticate correct keystroke
>do

>echo " ---------------------------------------"
>echo " -       Menusomething                         -"
>echo " - Hit (U)ser, (G)roup or (D)isconnect -"
>echo " ---------------------------------------"

>read menu
>if [ "${menu} = "u-U" ]; then
># should I use case instead? and what syntax makes u the same as U?

case "$menu" in
  u|U) ... ;;
  g|G) ... ;;
  d|D) ... ;;
  *) echo "you mistyped" ;;
esac

Quote:>PS: Thanks for helping me earlier. Scripting is a lot easyer than making C
>programs.
>Being not very educated I learn easyer by example (stealing or recycling)
>and links to already made scripts will be most welcome

--

Genuity, Woburn, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.

[...]
  > -------------------------------------------------
  > How do I check a username (or uid). I have tried man getuid, man uid etc.
  > and nothing comes up. Here is what I am trying to do:
  >
  > if [ "${User}" != "root" ]; then
  > # Only su may run this script
  >     echo " Im sorry, but you may not use this script"
  >     exit 1
  > else
  >     continue
  > fi
  > --------------------------------------------------

If the script can only be run with system administrator
privileges, it's a better idea to check for the numerical
user id instead of the login name. Although it's rare, there
may be other users with system administratore privileges.

The "id" command is suitable for this purpose.
Example output:

     $ id
     uid=500(heiner) gid=100(users)
     $ su -
     Password:
     # id
     uid=0(root) gid=1(other)

You could use "id" in the following way to check
for a user with user id "0" (= "root" privileges):

     case "`/usr/bin/id`" in
         "uid=0("*)   ;; # permissions are right
         *)         echo >&2 "invalid permissions"; exit 1;;
     esac

Heiner
--
  ___ _

\__ \  _/ -_) V / -_) ' \    Shell Script Programmers: visit
|___/\__\___|\_/\___|_||_|   http://www.shelldorado.com/

Quote:> It might be easier for you to read books on scripting than to post a
> question every time you stumble.  Otherwise you'll spend most of the next
> few months waiting for answers from the net.

Thanks for your answer.

I'm using "Linux in a nuttshell" and an old danish book on unix. Preaviously
posted links like http://linux.wuxi.net.cn/docs/shelllearn,
http://linux.nixcraft.com/lsst/ and google helped also helped me a lot. Any
suggestions for other material is most welcome.

It seems to me that what workes in some examples in books, doesn't always
work on my mashine (Probably my fault).
I have tried different shells, but now use the Gnome shell (Bash) and it
seems more compatible with the examples.

In hope of not annoying anybody with to simple questions.

regards from

Leif

Quote:>Being not very educated I learn easyer by example (stealing or recycling)
>and links to already made scripts will be most welcome

===============================================================================

Quote:

> Heiner

Tim

  >

  >>
  >>[...]
  >>  > -------------------------------------------------
  >>  > How do I check a username (or uid). I have tried man getuid, man uid etc.
  >>  > and nothing comes up. Here is what I am trying to do:
[...]

  > What, Heiner?!?!  You didn't EXPLICITLY direct him to shelldorado?
  >                   Don't want him 'stealing' or 'recycling' your stuff. :-)

Hey, I put the examples on the SHELLdorado because they
are intended to be "stolen" ;-)

Surprising as it seems, there is no script showing how to
check the user id at the SHELLdorado. I try to avoid
limiting the usage of a script to certain user ids, because

  (1) it's not safe, because the user could just create his own
      copy of the script, remove the check, and run it again

  (2) there could be other means of granting access permissions,
      not related to the user id. Example: Solaris' "Role Based
      Accounting" (RBAC), or ACLs

Heiner
--
  ___ _

\__ \  _/ -_) V / -_) ' \    Shell Script Programmers: visit
|___/\__\___|\_/\___|_||_|   http://www.shelldorado.com/

Quote:

>   (2) there could be other means of granting access permissions,
>       not related to the user id. Example: Solaris' "Role Based
>       Accounting" (RBAC), or ACLs

Quote:

> Heiner

Quote:>      # id
>      uid=0(root) gid=1(other)

~$ id -u
501
~$ echo "int geteuid() { return 0; }" > fakeid.c
~$ cc -shared -fPIC fakeid.c
~$ LD_PRELOAD=$PWD/a.out export LD_PRELOAD
~$ /usr/bin/id -u
0

case `/usr/bin/env -i /usr/bin/id -u; /usr/bin/env -i /usr/bin/id -ru` in
  0?0) echo "you are a previledged user";;
esac

--
Stphane

1) That a 'x=value export x' is acceptable syntax.

2) That $PWD is not reliable for all shells
   Cygwin/sh being the exception.  I prefer
   `pwd` anyway.

3) That my Cygwin cc/gcc compilers don't like -fPIC ...
   probably because Cygwin is not quite there yet.

4) That 'zsh' does not like statements contained
   wiin DOS-compatible text files.

5) That:

  echo "int geteuid() { return 0; }" > fakeid.c
  cc -shared -fPIC fakeid.c
  LD_PRELOAD="`pwd`/a.out" export LD_PRELOAD

  /usr/bin/id -u

  case `/usr/bin/env /usr/bin/id -u; /usr/bin/env /usr/bin/id -ru` in
    0?500) echo "you are a previledged user";;
  esac

  Actually works on Linux 2.8!  I like the way you think ...
  I'm putting a firewall in ASAP. :-)

Keep Up the Good Work!

Tim

[...]

  >>  (2) there could be other means of granting access permissions,
  >>      not related to the user id. Example: Solaris' "Role Based
  >>      Accounting" (RBAC), or ACLs
  >
  > I don't know what this means, frankly.  But I'm a little fatigued.

I'm feeling fatigued, too, after searching for RBAC information ;-)

RBAC ("Role-Based Access Control") is a Solaris way of giving users
certain privileges usually only "root" has (like "sudo"), or even to
diminish the permissions "root" has:

     http://docs.sun.com/db/doc/805-7229/6j6q8svdf?q=role+based+access+con...

I don't know if RBAC is part of a (POSIX?) standard, or
just Sun's way of solving this frequently seen problem.

Heiner
--
  ___ _

\__ \  _/ -_) V / -_) ' \    Shell Script Programmers: visit
|___/\__\___|\_/\___|_||_|   http://www.shelldorado.com/

Quote:> 2) That $PWD is not reliable for all shells
>    Cygwin/sh being the exception.  I prefer
>    `pwd` anyway.

`pwd` is not reliable because it doesn't work in directoies
whose name is terminated by newline characters.

Note that the pwd builtin and /bin/pwd may not give the same
results. Components of `pwd` (or $PWD) can be symlinks, that's
not the case in /bin/pwd output.

Quote:> 3) That my Cygwin cc/gcc compilers don't like -fPIC ...
>    probably because Cygwin is not quite there yet.

Anyway the geteuid can't be safe in a cygwin environment.

--
Stphane

eval "PWD='$(pwd |sed -e 's/'\''/&\\&&/g' -e '$s/$/'\''/' )"

Of course if a shell has not got POSIX command substitution it may be
difficult get the right syntax here, and otherwise it's pretty unusable
I suppose; but it does work, it's not broken.

Of course you do have an excellent point, the more natural;

PWD=$(pwd)

*is* broken.

elonex486$ cat >fil
+ cat
+ > fil

directory '1'

elonex486$ eval "PWD='$(cat fil |sed -e 's/'\''/&\\&&/g' -e '$s/$/'\''/' )"
+ cat fil
+ sed -e s/'/&\\&&/g -e $s/$/'/
+ eval PWD='
directory '\''1'\''
'
+ PWD=
directory '1'

elonex486$

byefornow
laura

--
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  The only case where I found PWD to be 'readonly' was in
  'zsh' version 3.0.8.  It must have been a problem, because
  in the 4.0.6 version it is not.  True, one would not alter
  PWD conciously, but there are such things as bugs. At least
  the 'pwd' command/built-in can't be accidentally assigned a
  value.

  Curiously, the SUN ksh(1) man page says of the 'pwd' built-in:

     pwd

         Equivalent to print -r - $PWD.

   I wonder if is true because, in my four Linux shells, the
   PWD variable can be assigned values without affecting
   the 'pwd' accuracy.

Quote:

> `pwd` is not reliable because it doesn't work in directoies
> whose name is terminated by newline characters.

   Rather than trying to treat the symptoms of embedded/terminating
   newlines, perhaps the problem should be addressed more directly
   by renaming all afflicted directories/files to meet an acceptable
   standard.

Quote:

> Note that the pwd builtin and /bin/pwd may not give the same
> results. Components of `pwd` (or $PWD) can be symlinks, that's
> not the case in /bin/pwd output.

Quote:

> Anyway the geteuid can't be safe in a cygwin environment.

Tim