Shell Programming and Scripting

I have a script like this called "remove.sh":

#!/usr/bin/ksh

rm remove.sh
echo "Deleted myself!"

Since UNIX is a scripting language I thought running it like " sh remove.sh" would generate an error/ or ANYTHING except the echo statements output. But the echo statement came out alright!
Since in this case I had spawned a sub-shell (using 'sh'), I tried running it as ". remove.sh" and it still worked.

Can anybody explain why?

Put this in a script and run it. It will delete itself.

Code:

#! /bin/rm -f

echo "This will never get printed...!"

vino

Thanks a lot Vino!

Could you also tell me why the previous version (the one I posted ) works (I mean, gives the echo output). I had thought the shell scripts were executed line-for-line without being stored in a temporary buffer.

Because the interpreter (the shell) loads the whole script and then executes it line by line. It would be really rather ineficient for it to repeatedly read a line and execute that line.

I tried the script by Vino. The line is getting printed and the file is not getting deleted. Im using OSF1 V5.1 732 alpha. I am using Korn Shell.

It works fine for me ... how are you executing the file?

If you are calling it like:

Code:

ksh remove.sh

then it will not work since you are foorcing the interpreter to be ksh where vino's example does not.

What do you have in your script and how are you involking it?

Ordinary shells behave like that, but ksh is much more efficient. To execute a loop, it ensures that it has the entire loop in core, then it compiles the loop and then it executes the compiled code. Other shells need to re-interpret the code on each iteration. This the secret of ksh's speed.

More than that, despite the name, rm does not remove files, it unlinks them from directories. If the file has zero links and is not open by any process, it is removed. So the file will not disappear while ksh has it open. Instead, it becomes a file with zero file names. This behavior is a good way to handle temporary files and a lot of programs do that... create a file, unlink it, then use it. It is guaranteed to disappear upon program exit.

Newbie admins post fairly often saying that a big file ate their filesystem, they deleted it, and they did not get the space back. This is why that happens. The file is still consuming space and will until the process that has it opened is killed. And now the file has no name so it is much harder to deal with.