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Old 04-30-2008, 09:15 AM   #1
fiona79us
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Can I Have Some Help Writing This Bash Script Since Is My First Time Doing One?


Write a script that extracs all the usersids from the /home directory
into a file along the the last login date.

NAME OF SCRIPT: usage.bas

EXAMPLE:
./usage.bas
 
Old 04-30-2008, 09:26 AM   #2
acid_kewpie
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no sorry, we can't help you from no starting point at all, that's called cheating. how far have you got of your own accord? ask us some specific question and we can give some specific advice, but we can't just write a script for you.
 
Old 04-30-2008, 10:54 AM   #3
forrestt
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First, you need to have an interpreter specified by your script. This is what the first line of the script does. That line begins with a #! to signify that it is to execute what follows as the interpreter. I suggest you use /bin/sh, but you can use whatever shell you like.

After that, you need to figure out what commands get usernames from /home and what commands get last login information. You will also need to determine what commands will help break up a many line output into subsets.

Study:

ls
last
head
awk

Notes:
Variables can be assigned by
VARIABLE=text
VARIABLE="Text with spaces"
VARIABLE=`command output`

You will need a for loop

for VARIABLE in `command output` ; do
...
...
...
done

If you get stuck, ask.

HTH

Forrest
 
Old 04-30-2008, 02:33 PM   #4
pixellany
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Here's a challenge: Write a script that automatically detects when someone does a cut and paste from the instructor's assignment sheet.

Seriously---to get help with homework, you should:
--acknowledge that it is homework
--show what you have already tried
--mention what textbook(s) you are using
--ask a question in your own words
 
Old 04-30-2008, 07:21 PM   #5
chrism01
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Actually, I'd recommend using
#!/bin/bash
for the 1st line. /bin/sh MAY be symlinked to /bin/bash, but it's not required, and in which case it'll actually be the POSIX sh shell ... which is not the same thing ...
 
Old 05-01-2008, 04:26 AM   #6
H_TeXMeX_H
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I think it's best to use '#!/bin/sh' because whatever it is linked to must be Bourne-shell compatible. What if you use ksh and don't even have bash installed ?
 
Old 05-01-2008, 10:13 AM   #7
fiona79us
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Well hello everyone, i think we started off on the wrong foot here, so let me start again...
I am not asking for anyone to solve this for me , i only need a guide on how to start. i have some small knowledge of linux but not on bash as much. so far i know that i have to use maybe ls -l/home/, i also know that i have to create a file and put all the users in there, i will start the script with

#!/bin/bash
#
 
Old 05-01-2008, 11:21 AM   #8
H_TeXMeX_H
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Remember to read man pages, for example 'man last'.

'head' will get the beginning of a file, for example 'head -n 1' will get the first line of a file. You must use the pipe '|' to pipe program output from one to another.

For example try this:
Code:
last | head -n 2 | tail -n 1
that should give a good start on things (maybe even solve everything).

Oh, and to redirect output into a file you can use the overwrite/create '>' or append '>>'. For example 'last | head -n 2 | tail -n 1 > /home/$USER/testing-script'.

Here are some good guides, study them well:
http://www.grymoire.com/Unix/
http://tldp.org/LDP/abs/html/

EDIT: It might take you a while to figure awk out, so I'll give you a hint ... piping to
Code:
awk '{ print $2 }'
will print the second tabbed entry of program output stream.

That's all I can say, if you put all that together, it's more than enough to figure it out. Remember, read the guides.

Last edited by H_TeXMeX_H; 05-01-2008 at 11:25 AM.
 
Old 05-01-2008, 05:45 PM   #9
fiona79us
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Quote:
Originally Posted by H_TeXMeX_H View Post
Remember to read man pages, for example 'man last'.

'head' will get the beginning of a file, for example 'head -n 1' will get the first line of a file. You must use the pipe '|' to pipe program output from one to another.

For example try this:
Code:
last | head -n 2 | tail -n 1
that should give a good start on things (maybe even solve everything).

Oh, and to redirect output into a file you can use the overwrite/create '>' or append '>>'. For example 'last | head -n 2 | tail -n 1 > /home/$USER/testing-script'.

Here are some good guides, study them well:
http://www.grymoire.com/Unix/
http://tldp.org/LDP/abs/html/

EDIT: It might take you a while to figure awk out, so I'll give you a hint ... piping to
Code:
awk '{ print $2 }'
will print the second tabbed entry of program output stream.

That's all I can say, if you put all that together, it's more than enough to figure it out. Remember, read the guides.
thank you

i'm gonna try and let you know the outcome

Fiona
 
Old 05-01-2008, 07:00 PM   #10
chrism01
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More useful links:
http://tldp.org/LDP/Bash-Beginners-G...tml/index.html
http://rute.2038bug.com/index.html.gz

Let us know if you get stuck

Last edited by chrism01; 05-01-2008 at 07:05 PM.
 
Old 05-01-2008, 07:05 PM   #11
chrism01
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H_TeXMeX_H, can you prove that 'it's best to use '#!/bin/sh' because whatever it is linked to must be Bourne-shell compatible.' ?
AFAIK, it's like I said, it MAY link to bash (or soemthing else) or it's the POSIX sh, but there's no rule saying which or whether what it points to has to be compatible with anything else.
If you can show me link proving otherwise I'd be glad of the update. (seriously)
 
Old 05-01-2008, 07:27 PM   #12
forrestt
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chrism01, I think the point he is making (which is the same reason I said /bin/sh) is because you will always have /bin/sh on your system. You can't guarantee you will have bash.

Forrest
 
Old 05-02-2008, 11:53 AM   #13
H_TeXMeX_H
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Quote:
Originally Posted by forrestt View Post
chrism01, I think the point he is making (which is the same reason I said /bin/sh) is because you will always have /bin/sh on your system. You can't guarantee you will have bash.

Forrest
Yes, indeed.

What you must understand is that '/bin/sh' will not exist as a real file, it will always be a symlink on modern systems. It will be a symlink to a Bourne compatible shell such as bash or ksh. You can use '/bin/bash' without any problems on most systems. Also, sh and bash are never installed simultaneously on one system, just bash is installed. If sh is installed, the system is ancient and the script will fail in most cases anyway.

To try to summarize it:
The greater concern here is not that sh will exist as the original Bourne shell, it will not. The greater concern is whether bash will exist or will it have been replaced by ksh or some other shell.

I have no real links to veriy whether my way is better, but I think it's better. You can do whichever you think is better. I always use '/bin/sh' because I know this is never the old sh Bourne shell, it's always bash or ksh.
 
  


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