Exploring Expect

Arrays

Earlier, I described how multiple strings can be stored together in a list. Tcl provides a second mechanism for storing multiple strings together called arrays.

Each string stored in an array is called an element and has an associated name. The element name is given in parentheses following the array name. For example, an array of user ids could be defined as:

set uid(0)                "root"
set uid(1)                "daemon"
set uid(2)                "uucp"
set uid(100)                "dave"
set uid(101)                "josh"
. . .

Once defined, elements can then be accessed by name:

set number 101
puts var "User id $number is $uid($number)"

You can use any string as an array element, not just a number. For example, the following additional assignments allow user ids to be looked up by either user id or name.

set uid(root)                    0
set uid(daemon)                    1
set uid(uucp)                    2
set uid(dave)                    100
set uid(josh)                    101

Because element names can be arbitrary strings, it is possible to simulate multi-dimensional arrays or structures. For example, a password database could be stored in an array like this:

set uid(dave,uid)                            100
set uid(dave,password)                            diNBXuprAac4w
set uid(dave,shell)                            /usr/local/bin/zsh
set uid(josh,uid)                            101
set uid(josh,password)                            gS4jKHp1AjYnd
set uid(josh,shell)                            /usr/local/bin/tcsh

Now, an arbitrary user’s shell can be retrieved as $uid($user,shell). The choice of a comma to separate parts of the element name is arbitrary. You can use any character and you can use more than one in a name.

It is possible to have element names with whitespace in them. For example, ...