UNIX for Dummies Questions & Answers

Hi,

In the beginning of Shell script, we give a statement like
#!/bin/ksh

I have 2 questions related to this,

1) It could denote about the shell we want to use, what is the real usage of this? My shell script works even without this statement, is it a mandatory one.

2) I'm using bash shell, for this, can I give it as #!/bin/sh

Please advise.

Thank you.

Hi,

Thank you for the link.

Can you put it in your own terms with examples.

Why? Is this an interview question? Or home-/coursework? If you've got problems with understanding the article, please state them, instead of asking generalized questions.

???

Link seems pretty clear to me, including the examples. How would you like it worded or expanded?

In a nutshell, the first 2 characters happen to be the ascii representation of the hex values 0x23 0x21 which is a "magic number" that the shell interpreter uses. When the interpreter sees the #! as the first 2 characters, it builds a command line consisting of the remaining characters after the #! followed by the filename itself along with any values passed to it. i.e. for the following script called show_message:

Code:

#!/bin/ksh 
print $1

called like this:

Code:

show_message "hello world!"

The actual command line run by the system would be:

Code:

/bin/ksh show_message "hello world!"

The command after the #! does not have to be a shell either. Try this script:

Code:

#!/bin/ls -l

or this:

Code:

#!/bin/rm
print This will not show because the script is deleted on the first line

No, do not do that. If this is a script that you wish to truly run using the bash shell, use #!/bin/bash. The practice that arose in the Linux community of using #!/bin/sh to mean bash is simply a bad practice.