Is there any practical difference between unsetting an environment variable and setting it to the empty string?
Each application is free to interpret an unset variable and an empty variable in the same way or not. It is generally a bad idea to give them different meanings, and most applications don't do it, but it happens.
An example in shells themselves is the
In a shell script,
There is a difference, yes. But it is very subtle since evaluating an empty string and an unset variable are the same.
Both will have
One thing that I commonly use this for is to set up a
In higher level languages, like Perl and Python, this is the difference between "" and undef (Perl) or None (Python).