Which shell language should I use?

[gsg0384 at uxa.cso.uiuc.edu]

Hi,

I simply thought that I should use the C-shell script language since
I am using /bin/csh as an interactive shell.  But
I found, and was surprised, that most shell script files are Bourn-shell 
script files.  Even some of the Berkely-originated source were
wriiten in Bourn-shell language.

1. How much of the Berkeley-originated script files were written 
in Bourn-shell language?

  It seems to me that such practice enhances
portability.  I'd like to hear some opinion on which shell-sript
language is preferable for what purpose.

2. I found that the first line of a shell-script file is special
   even though it contains '#'.  Sometimes I found, and sometimes not,

#!/bin/csh

  or

#!/bin/sh

   in the first line.  They looks like directives.  Am I right?

3.  Where in the UNIX manual can I find some kind of rule on which
   shell-script parser is applied for a certain shell-script file?

4. Please recommend a book on shell programming.

Thanks a lot.

             Hugh
             gsg0384 at uxa.cso.uiuc.edu