Questions[strings](server)

Is there a portable unix shellscripting way of joining a number of strings together with a given separator, like so:

$ strjoin --- foo bar baz quux
foo---bar---baz---quux

Sure I could use a $scripting_language one liner or an ugly explicit loop in a shellscript function, but the unix hackers of old probably had some need for this as well, so someone has made a standard command like this that I don't know about somewhere in the past, right?

edit

The sed method is certainly the easiest one in many situations, but it doesn't work if the strings can contain spaces. And many of the other answers also don't handle that. Are there any solutions other than the $IFS trick that handle spaces (and all possible characters in general) and do not require writing a full loop?

How do I store the last part of directory in a variable?

For example I have the following path: A\B\C\D, I want to store D in variable like file_name=D.

I try to extract the hostname from the following string (created using who am i):

username pts/0        2010-10-05 17:30 (www.example.com)

I need a solution which also works if (www.example.com) is not present which is the case when I am logged in locally. Furthermore the solution also has to work on a Mac where who am i returns the following string:

username ttys006      Oct  5 16:47 (www.example.com)

The problem is that the mac puts spaces in the date which makes it hard to use cut. I think, there must be a solution using sed to extract the substring, but I have problems figuring out how to use sed appropriately.

Update: Mad's approach

This approach only works well if there are actually parentheses present. If not, the following happens:

$ who am i | cut -f2 -d '(' | tr -d ')'
username ttys006      Oct  5 16:47

im making a script like sudo, the idea is that the sudo function is going to run a scriptblock in elevation. I'm having trouble with the strings variables, that i pass in that scriptblock. Is like the doubles quotes disappear. What is wrong with my approach? Here is the code.

function sud([ScriptBlock]$SomeCode){
$here = Get-Location;
Start-Process Powershell -Verb Runas -ArgumentList "-command &{cd $here; $SomeCode}" 
}

and i want to run commands like this:

$var ="Path"
$newpath = $env:path + ";c:\somedir"
$target = "Machine"
sud -somecode { [Environment]::SetEnvironmentVariable($var, $newpath, $target)}

for testing purpose one can add the parameter -noexit to the argumentlist..

Start-Process Powershell -Verb Runas -ArgumentList "-noexit","-command &{cd $here; $SomeCode}" 

Is there any linux command to extracts all the ascii strings from an executable or other binary file? I suppose I could do it with a grep, but I remember hearing somewhere that such a command existed?