===============================================================================
5 - Practical Scripting Examples.
===============================================================================

I'd first like to add a note which you already probably knows:
./ == look in current directory instead of the "PATH".
To give that an example, say now that you have a script in your home
directory called "ls" or "dir", how would you execute that without
getting the contents of the directory ?
well, that's why you use "./"  before a name to execute it if it's in the
current directory.
../ == previous directory (one directory further up towards "/" then you are
currently in), this can be used as this, say that you have a script called
"script" in "/home/user/" and you are standing in "/home/user/nice/" and
you don't want to leave the directory but still want to execute the script.
Then you do, "../script" and if you are in "/home/user/nice/blah/" you
you would do, "../../script" ----- "../../" == 2 directory's back.
Get the idea ?

Anyway, now to the practical examples, which are working scripts for
various purposes, to give an idea about what you can do with shell scripting.
New things previously not explained will show up in this section, but
I will explain them as we go along.

Let's start with simple examples and move on to harder parts.
As for first I'll stick to useless scripts =) just for illustration.
Explanation on the scripts follow after them, as usual.
So here we go on that.

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#!/bin/bash

one="$1"
something="$2"

if [ "$one" = "" ]; then
echo "Usage: $0 [name] <anything goes here>"
exit 0
fi

function first {
clear
echo "this is a test script !"
echo
echo "name followed on $0 was - $one - "
echo
echo "if you typed anything after the name it was: $something"
echo
}

first

exit 0

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Executed without any thing after the script name it looks like this:

alien:~$ ./script
Usage: ./script [name] <anything goes here>
alien:~$

Executed with a name it looks like this:

alien:~$ ./script Jerry
----------------------------------------
this is a test script !

name followed on ./script was - Jerry -

if you typed anything after the name it was:

alien:~$

Executed with a name and something else it looks like this:

alien:~$ ./script Jerry homer
---------------------------------------
this is a test script !

name followed on ./script was - Jerry -

if you typed anything after the name it was: homer

alien:~$

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Notes: $0 == the script name's variable so you can do a "Usage: <scriptname>"
       whatever the script is named after you made it.
       $1 == the first thing that's typed after the script in the command line
       $2 == the second thing that's typed after the script in the command line
       $3, $4 and so on .....

       one="$1" this puts the contents of "$1" into the variable $one
       which can be very useful to avoid errors.

       clear == clears the screen

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This next example is a script which you really shouldn't use...
It's here as an example for a working help script, but *could*
cause harm if not used correctly.
So if you loose anything because of using it, it's all on you.
and don't say I didn't warn you.

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#!/bin/bash

if whoami | grep -v root >> /dev/null; then
    echo "you have to be root to use this"
 exit 1
else

cat /etc/passwd | cut -f1 -d : | grep -v halt | grep -v operator |
	grep -v root | grep -v shutdown | grep -v sync | grep -v bin |
	grep -v ftp | grep -v daemon | grep -v adm | grep -v lp |
	grep -v mail | grep -v postmaster | grep -v news  | grep -v uucp |
	grep -v man | grep -v games | grep -v guest | grep -v nobody > user.list
fi

for USER in `cat user.list`; do
 if cat /home/$USER/.bash_history | grep passwd >> /dev/null; then
    echo
    echo "user $USER have tried to access the passwd file"
    echo "do you want to remove $USER from your system [y/n] "
read YN
 if [ "$YN" = "y" ]; then
    echo "user $USER is being deleted"
    echo "home dir of user $USER is however intact"
    echo
    remuser $USER
 else
    echo "user $USER is not deleted"
    echo
 fi
else
    echo "$USER haven't tried to access the passwd file"
 fi
done

 rm user.list
    echo
    echo "Script finished"
    echo
exit 0

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I will just translate this script into real/clear English:

if (check own user-name) is anything else but root >> send output to a black hole
say, "you have to be root to use this"
terminate program.
in other cases (in this case that can only be if the user is root)

list the contents of the file "/etc/passwd" combined with - cut out the
user names (field 1 separated by ":") grep everything except lines containing the
following words/names: halt operator root shutdown sync bin ftp daemon
adm lp mail postmaster news uucp man games guest nobody and send it
to the file "user.list"
end "if" statement

for each user in the "user.list" file do the following
if the word "passwd" is present in "/home/$USER/.bash_history" >> output to
the systems black hole
say nothing
say "user $USER haver tried to access the passwd file"
say "do you want to remove $USER from your system [y/n]"
read if the input from the keyboard is a "y" or "n"

if the variable for the answer of the input is "y" then
say "user $USER is being deleted"
say "home dir of user $USER is however intact"
say nothing
removing the user from the system that tried to access the passwd file
in other cases
say "user $USER is not deleted"
say nothing
end "if" statement
in other cases
say $USER haven't tried to access the passwd file
end "if" statement
exit the for-loop

remove the "user.list" file
say nothing
say "Script finished"
say nothing

exit and return to the shell command line.

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Note: grep -v == show everything *except* what comes after the -v

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Here is another way of doing the exact same script, just to illustrate that
the same thing can be done in several different ways:

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#!/bin/bash

if [ "$UID" != "0" ]; then
    echo "you have to be root to use this"
    exit -1
fi

for uids in `cat /etc/passwd`; do
    useruid=`echo "$uids" | awk -F':' '{print $(3)}'`
    test "$useruid" -ge "500" 2>/dev/null &&
    echo "$uids" | awk -F':' '{print $(1)}' > user.list
done

for USER in `cat user.list`; do
    if (grep passwd /home/$USER/.bash_history >/dev/null); then
       echo
       echo "user $USER have tried to access the passwd file"
       echo "do you want to remove $USER from your system [y/n] "
       read YN

       case $YN in
            y* | Y*)
	       echo "user $USER is being deleted"
    	       echo "home dir of user $USER is however intact"
    	       remuser $USER
	       echo
	       ;;
            n* | N*)
	       echo "user $USER is not deleted"
	       echo
	       ;;
       esac
    else
       echo "$USER haven't tried to access the passwd file"
       rm -f user.list
       echo
       echo "Script finished"
       echo
    fi
done

exit 0

-------------------------------------------------------------------------------

Since this script does the exact same thing, but in another way, I'll leav you
with the experiance of trying to figure out the differences and how it
works with the help of this tutorial, you might not get this right until
you've read this tutorial twice.

A tip is: try to make a comment to each line with what it does and why.

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This below script is a "Wingate" scanner, to scan for wingates that can
be used to bounce off and such things, don't know if that's really legal
so take that on your own risk.

Anyway here comes the script:

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#!/bin/bash
echo > .log.tmp
echo > .log2.tmp
echo "sleep 7" > wg.config
echo "killall -2 telnet" >> wg.config

scan="$1"
count="0"
max="255"

clear

if whoami | grep root >> /dev/null ; then
   echo "please use this as user and not root, since it would kill all users"
   echo "telnet sessions"
 else
clear
fi

if [ "$1" = "" ]; then
        echo " usage is: $0 <C host> "
        echo "  examples:"
        echo "  $0 127.0.0"
        echo " That will scan from 127.0.0.0 to 127.0.0.255"
        echo
        echo "be aware though, while it scans it also kills any other telnet"
        echo "sessions you might have ...."
 exit 0
fi

while [ "$count" != "$max" ]; do count=`expr $count + 1`
        echo "Attempting connection to $1.$count "
        echo > .log2.tmp
        ./wg.config &
        telnet $scan.$count >> .log.tmp
        cat .log.tmp | grep -v refused | grep -v closed | grep -v Connected | grep -v Escape | grep -v login >> .log2.tmp
        echo >> .log.tmp
    done
  echo "Script Finished, results stored in .log.tmp and .log2.tmp"
exit 0

-------------------------------------------------------------------------------

This time I will not translate the script into clear English and I will
not show how it looks executed, I leave that for you to do =)

------------------------------------------------------------------------------

Now a final practical example of a script, this is a small graphical front end
to the console mp3 player `mpg123` so you got to have that to work
and you need to execute this script in a directly where you have mp3's ....
Also if you want the X-windows part of it to work you need to get and
install Xdialog, you can get that from www.freshmeat.net ...
However if you have Linux Mandrake you should be good anyway, Xdialog
comes as default in Mandrake.
This script should be named `xmpg123`.
So here we go:

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#!/bin/bash
dialog --backtitle "xmpg123"
       --title "Main menu"
       --menu "Make your choice" 13 60 6
        1 "X-windows"
        2 "Ncurses"
        3 "Exit" 2> .tempfile
        output=`cat .tempfile`
        echo $output
        rm -f .tempfile

if [ "$output" = "1" ]; then
for songs in `ls -1 *.mp3`; do
echo "$songs mp3-file" >> .tempfile
done
output=`cat .tempfile`
Xdialog --menu 2 2 2 1 $output
        2> .tempfile
        output=`cat .tempfile`
        mpg123 $output
        rm -f .tempfile
fi

if [ "$output" = "2" ]; then
for songs in `ls -1 *.mp3`; do
echo "$songs mp3-file" >> .tempfile
done
menu=`cat .tempfile`
dialog --menu "Make your choice" 13 70 6 $menu 2> .tempfile
       output=`cat .tempfile`
       mpg123 $output
       rm -f .tempfile
fi

exit 0

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A note being that dialog and Xdialog seems to be in early stages, so this
may look sort of buggy if you don't have the great dialog god at your side...

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And don't forget to "chmod u+x <script name> or chmod a+x <script name>

to make your scripts executable.