Re: [MLUG] shell script - find shell script parent directory?

[Mike Miller <EMAIL:PROTECTED>]

On Tue, 4 Mar 2008, Jonathan King wrote:

> > #!/bin/bash
> > ( cd "${0%/*}" ; pwd -P )
> >
> > That is very cool and it is similar to what we came up with on TCLUG. 
> > There are several little tricks worth adding though.  What happens if 
> > the filename or directory name begins with a minus sign?
>
> I guess you could escape it...

Suppose you want to make a directory name that begins with "-".  Will this 
work?

mkdir \-X

Nope.  A few days ago, I thought it would, but it doesn't.  This is where 
the "--" argument comes in:

mkdir -- -X

That works.  The same trick works for "cd", so we're up to this:

#!/bin/bash
( cd -- "${0%/*}" ; pwd -P )

But, if you try that on a directory beginning with "-" it will still fail! 
The reason is that it tries to treat the dirname as an argument to *bash*. 
That one surpised me.  So you can do this to avoid trouble:

#!/bin/bash --
( cd -- "${0%/*}" ; pwd -P )

Pretty weird.  I did not know about that.  I guess we should always use 
"bash --", right?  Unless, of course, we want to provide bash arguments on 
the command line.


> > How can we be sure that the bash builtin versions of cd and pwd are 
> > used?
>
> Can you over-ride that from happening? In any case, a horrible hack 
> would be to parse the output of "which", which should report that these 
> are built-ins. Note: I don't have a appropriate test bed here at work 
> for any of this.

The key here is that there is a bash command called "builtin".  We can use 
it like so:

#!/bin/bash --
( builtin cd -- "${0%/*}" ; builtin pwd -P )

All that's left now is to make a variable called EXEC_DIR to hold the 
info, then echo that to stdout.

Mike

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