How to undefine and unset a bash environment variable on Linux or Unix

varName=someValue
export varName
export vech="Bus"
echo "$vech"

How do I unset a variable in bash?

Use unset command to delete the variables during program execution. It can remove both functions and shell variables. The syntax is:

unset varName

To unset the $vech, enter:

unset vech

Verify it:

echo $vech

A note about readonly variables

Please note that some variables cannot be unset if they are defined as readonly by the system or sysadmin:

unset BACKUPDIR

Sample outputs:

-bash: unset: BACKUPDIR: cannot unset: readonly variable

You can define your readonly variables using the following syntax:

declare -r BACKUPDIR="foo"

How do I unset a shell function on bash?

The syntax is as follows to treat each varName as a shell function:

unset -f varName
unset -f tarhelper

For more info, type:

$ help unset
$ help declare
$ man bash