4.5 First Shell Script

4.5 First Shell Script

1. Create the following shell script file called cmd using the pico (or vi) text editor:

   #!/bin/bash
   echo your-name
   echo TABER CIS137
   echo Lab 4.5: UNIX shell script                     
   echo -n "pwd        >> "         
   pwd                               
   echo -n "who am i   >> "           
   who am i                            
   echo "id            >> "   `id`      
   echo '$HOME         >> ' $HOME        
   

   To do this use the command:

   username@gort ~ $ pico cmd
   

   Please note that the "id" is surrounded by grave accents, not single quotes. Also note that the string:

   $HOME        >>  
   

   is quoted by single quotes, not grave accents.
2. When you have finished, verify your work with the following command:

   username@gort ~ $ cat cmd
   

   This command, cat, is short for catenate. It is the UNIX "type" command. It can also be used to concatenate files together. The output you get from this command should match the file shown above.
3. Try to run your shell script. This should fail. It might fail in a different way. The example below assumes that you are running bash. You might just get permission denied if you are running csh.

   username@gort ~ $ cmd 
   bash: ./cmd: Permission denied
   

4. Check the file protection bits. Use the ls command. This is the UNIX "dir" command. The -l is an option for the "long" format output.

   username@gort ~ $ ls -l cmd 
   -rw-r--r--  1 ltaber    167 Jan 16 10:21 cmd 
   

   This is showing that I, the user, have read and write access. My group has read access. Everyone else also has read access. No one has eXecute permission.
5. Change the protection bits. To give everyone eXecute permission, use the chmod command:

   username@gort ~ $ chmod a+x cmd
   

   The chmod command also takes octal arguments, for example:

   username@gort ~ $ chmod 755 cmd
   

   I find the symbolic names easier to remember.

   r    read
   w    write
   x    eXecute
   u    user
   g    group
   o    other
   a    all users (user, group, and other)
   +    add permission
   -    remove permission
   =    set permission
   

6. Check the protection bits.

   username@gort ~ $ ls -l cmd
   -rwxr-xr-x  1 ltaber          167 Jan 16 10:21 cmd 
   

   Note the new x's in the permission bits.
7. Run your shell script and check your output.

   username@gort ~ $ cmd
   
   Louis Taber
   TABER CIS137
   Lab 4.5: UNIX shell script
   pwd        >> /home/ltaber 
   who am i   >> ltaber pts/0        Aug 21 08:24 (:0.0) 
   id         >> uid=69(ltaber) gid=10(staff) 
   $HOME      >> /home/ltaber 
   
   username@gort ~ $ 
   

   You may need to edit the shell script and try again. If you do, you will not need to set the eXecute bits a second time. Once is enough. UNIX keeps the existing protection bits. The location of the file will not change so a rehash is not necessary.
8. Print out a copy of your results (when your output is correct). There are two ways to print out your results:
    
   1. Pipe your cmd's output into the print program. To do this, use the pipe symbol "|". The command will look like:
   2.  

      username@gort ~ $ cmd | lpr
      

   4. printing a file Create a temporary file by using re-direction. Then print the file. The output redirection symbol is ">". When used with an exclamation point, it can be used to over-write an exisiting file. (">!"). The commands will look like this:

      username@gort ~ $ cmd >! temp 
      username@gort ~ $ lpr temp
      

   The print command may be lp on your system. To look at the printer queue use the lpq command.

your-name
Lab 4.5: First Shell Script
TABER CIS137

4.5 First Shell Script