Difference between 'svn update' and 'svn checkout'

Hi guys,

I've just started to use Subversion a few months ago and I am really
are asking me why I had never used it before but it is not the reason
of my contact. To be honest I am trying to to do a post-commit script
that automatically sincronizes a given workcopy when any of my users
commits their modifications to my repository.

Although it's is ok and working fine (at least in my simples test), I
did not put in production yet because I have a doubt that neither
Subversion manual or Google were able to answer me. I didn't find any
difference beetwen 'svn update' and 'svn checkout' commands which is
the main function of my post-commit script.

Nowadays I'm using 'svn checkout' and it is working, like I said, but
I'm not sure if I'm losing some functionality with this option.

Can anyone help me and answer my question?

regards.

-- 
Welington Rodrigues Braga
--------------
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Linux User #253605
"Em tudo somos atribulados, porém não angustiados; perplexos, porém
não desanimados; perseguidos, porém não desamparados; abatidos, porém
não destruídos;" - 2Co 4:8,9