Environment variables

Thanks to Michael Grant for getting me started (previous question).

Here's the conceptual pothole I'm currently in...

I want to set up the PATH variable for psql. I might even understand why.

I've got a .tcshrc file in my home directory.

I know how to modify the .tcshrc file to include the relevant line...
"setenv PATH /usr/local/psql/bin"

However, .tcshrc already has a PATH variable which I don't want to lose...
"setenv PATH "$PATH":/Library/MySQL/bin"

So, can I just add the new line to the file? If so, how do psql and
MySQL know which is which, given that they have the same name?

Or, are they mutually incompatible - I can have one or the other but not both?

Or, are multiple PATH variables traversed until something makes sense
to whatever it is that reads them?

In my csh.login file I have the following PATH variable...
"setenv PATH "/bin:/sbin:/usr/bin:/usr/sbin""

...and if I execute the terminal command "echo $PATH" I get...
"/bin:/sbin:/usr/bin:/usr/sbin:/Library/MySQL/bin"

...from this I deduce that I may be able to concatenate the paths in
.tcshrc into something like...
"setenv PATH "$PATH":/Library/MySQL/bin:/usr/local/psql/bin"
...is this correct?

Why is the syntax of these PATH variables different anyway? Is this
something specific to each of those programs or does
csh/tcsh/unix/macos allow two different syntaxes (syntaxi?) for the
setenv command (i.e. is setenv an attribute of tcsh or of psql and
MySQL)?

Yup, I don't have the O'Reilly book "csh and tcsh". It's nearly 1am
in London and the shops are closed. As ever, the two books that I do
have are telling me just enough to get me into trouble and not enough
to get me out again.

What websites should I be looking at to answer these kind of
questions without flashing the cash? Apple.com Support just shrugs
when I enter tcsh as a query.

TIA
Roy
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Roy MacGregor Paterson
MacGregorTech

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