Creating a User-Defined Variable
You can create your own custom, user-defined variables in Linux by simply
assigning a value to a new variable that you name. This may be useful when
you are doing some more advanced shell scripting or find you’re often using
a long command that you get tired of typing over and over.
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Chapter 7
The syntax is straightforward: enter the name of your variable, followed
by the assignment symbol (
=
) without a space, and then the value to put in
the variable, as shown here:
kali >
MYNEWVARIABLE="Hacking is the most valuable skill set in the 21st century"
This assigns a string to the variable
MYNEWVARIABLE
. To see the value in
that variable, use the
echo
command and the
$
content symbol with the vari-
able name, as we did earlier:
kali >
echo $MYNEWVARIABLE
Hacking is the most valuable skill set in the 21st century
Just like our system environment variables, user-defined variables must
be exported to persist to new sessions.
If you want to delete this new variable, or any variable, use the
unset
command. Always think before deleting a system variable, though, because
your system will probably operate much differently afterward.
kali >
unset MYNEWVARIABLE
kali >
echo $MYNEWVARIABLE
kali >
As you can see, when you enter
unset MYNEWVARIABLE
, you delete the vari-
able along with its value. If you use
echo
on that same variable, Linux will
now return a blank line.
Summary
You might find environment variables foreign, but it’s worth getting to know
them. They control how your working environment in Linux looks, acts,
and feels. You can manage these variables to tailor your environment to
your needs by changing them, exporting them, and even creating your own.
In some cases, they may be useful for covering your tracks as a hacker.
Managing User Environment Variables
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