[Basic Query]bsh script in tcsh shell

Shell Programming and Scripting
1

I am a beginner (Just 2 days old:o ), i will really appreciate if you can solve my silly queries as below:

Lets say i write a script like this

#!/bin/bsh
clear
#to read name from keyboard
echo "your name please.."
read fname
echo "you just entered $fname"
exit 0

My environment is set to work in tcsh.
My query are:
a) how does placing !/bin/bsh as comment results in its execution as bsh shell? AS i am a beginner, i need to know if it is an exception ? how does placing a path as comment affects the execution of code.

b)If, say i place the path as second line of my comment. assume my first two lines are as below

#just comment
#!/bin/bsh

The code executed, but i also get some errors which says command not found.

c) Is it compulsorily to place "exit 0" at the end of every script? where should it be used?

2

The "shebang" line is not an ordinary comment (btw do you mean #! /bin/bash)
It instructs the shell that executes the script which interpreter to call on the script when it is the first line of the script.

The value you exit from a script sets $? in the parent shell, this can be used to "report" an error in the running of the script to the parent or to make decisions based on the exit status.

A facile example which checks for the existence of the user in /etc/passwd before running the useradd program.

seterr.sh
8<------->8
#!/bin/bash
exit 1

verified_useradd.sh
8<--------------------------->8
#!/bin/bash
found_user=$(grep -e  "^$1:" /etc/passwd)
if [ "X$found_user" == "X" ] ; then
    # no such user in /etc/passwd yet
    /usr/sbin/useradd $i
    exit 0
else
    echo "User $i exists, please retry with a new user name"
    exit 1
fi


new_user
8<-------->8
seterr.sh
while [ $? -ne 0 ] ;do 
   echo "Please priovide a username"; 
   read uname; 
   verified_useradd.sh uname;  
done

In the example above the while loop will continue until verified_useradd.sh returns with no error, thus guaranteeing a user has been added (or at least that useradd was called

3

Hey,
I meant #!/bin/bsh only, and its working.

Thanks for introducing the concept of shebang, I wasn't aware of it.