Treat a Command as a Function

This addresses a generic question, best illustrated by an example.

The command 'tr' translates or strips characters from the contents of a file. Like most commands, it reads and writes files, or standard IO. For example, to strip spaces use:
% tr -d " " < in-file > out-file

How can we use a command like 'tr' in a shell script, to strip spaces from the contents of a variable? The effect we want is as if we could say:
var = tr ($var);

The secret is to stream the value of the input parameter, and capture the output stream, thus:


In tcsh use:
set var=`echo $var | tr -d " "`

In sh use:
var=$( echo $var | tr -d " " )