Basics 3: lists and foreach

Lesson: the list is THE data structure

Tool shells hand you almost everything as a list: the cells matching a pattern, the ports of the design, the clocks. In Tcl (Tool Command Language), a list is just a string of whitespace-separated words, and braces make literal ones:

set masters {BUF_X1 INV_X1 DFF_X1 NAND2_X1}

The core list commands:

llength $masters          ;# 4          (number of items)
lindex $masters 0         ;# BUF_X1     (zero-based indexing)
lindex $masters end       ;# NAND2_X1   ('end' is a real index)
lappend masters AOI21_X1  ;# append in place (note: no $ on the name)

lappend takes the name of the variable (no $) because it modifies it. Reading commands take the value ($masters).

Iteration is foreach:

foreach m $masters {
    puts "master: $m"
}

The body runs once per item with m bound to it. In tool scripts you will constantly write this exact loop over [get_cells ...] (the shell variant foreach_in_collection from the interview problems behaves the same way).

One brace rule to internalize: the opening { of a body must sit on the same line as the command (foreach ... {). Unlike C, putting it on the next line is a syntax error, because a newline ends a command.

Task

Starting from the list in the starter file, print exactly:

count: 4
first: BUF_X1
last: NAND2_X1
- BUF_X1
- INV_X1
- DFF_X1
- NAND2_X1

First three lines via llength and lindex (use end for the last), then one - line per item via foreach.