Creating a variable

The shell also lets you create variables. A shell variable name can consist of uppercase or lowercase letters, plus digits and the underscore character _. The name can have any length, but the first character cannot be a digit. Uppercase letters are distinguished from lowercase ones, so NAME, name, and Name are all different names.

To create a shell variable, just enter:

name='string'

as a command to the shell. No spaces are allowed around the =. For example:

HOME='/usr/macneil'

sets up a variable with the name HOME and the value /usr/macneil.

After you set a variable, you refer to it by prefixing its name with a dollar sign ($). Any command can use the value of a variable by referring to it this way. For example, if HOME is set to /usr/macneil:

cd $HOME

is equivalent to:

cd /usr/macneil

Similarly:

cp $HOME/* /newdir

is equivalent to:

cp /usr/macneil/* /newdir

To change the value of an existing variable, you use a command with the same form as the existing variable. For example:

HOME='/usr/benjk'

changes the value of HOME from /usr/macneil to /usr/benjk.

If the value on the right-hand side of the = sign does not contain spaces, tab characters, or other special characters, you can leave out the single quotation marks. For example, you can enter:

HOME=/usr/benjk