Overview

• Preliminaries.
  • Admin.
  • Questions.
• A quick review of Make.
• Automatic variables.
• Generic rules.
• Another example: Document development.
• How do I use other people's code?
• Standard make rules.
• Other useful techniques.
• Miscellaneous tools and techniques.

Preliminaries

Admin

• We'll spend a few minutes looking at your homework assignments.
• Homework: Create a full make suite for some useful C project, including options for cleaning, packaging, and more.
• Tomorrow's CS table is on lambdas in Java 8.
• Cool CS talk today at 4:30 p.m.

Questions

Sample Makefiles

AK

    CFLAGS = gcc -Wall -ggdb3

Traditionally, the CC command goes separately, so

CC = gcc CFLAGS = -Wall

    all: upperToLower

    upperToLower : upperToLower.c charUtils.o charUtils.h
    ${CFLAGS} -o upperToLower upperToLower.c charUtils.o

Usually we put .o files in the target.

    charUtils.o : charUtils.c charUtils.h
    ${CFLAGS} -c charUtils.c

Another one

    .PHONY : clean
    clean:
            -rm -rf *.o

Why the - before rm? We're not sure. Traditionally, make stops with the first consequent that fails. The - says "keep going".

What happens if we drop the .PHONY? Then Make won't run the rule when a file named clean exists and is up to date.

Sam discusses chmod

chmod sets permissions on files and directories.

You can use mnemonics

You can use three digit octal numbers

Each digit: 4 - read, 2 - write, 1 - execute

• First digit: User
• Second digit: Group
• Third digit: All users

Execute generally means "run a program". For directories, it means something about "can access elements of the directory."

A quick review of Make

• Tool for automating construction of projects
• Three basic concepts:
  • Targets (files or actions)
  • Prerequisites
  • Actions

• Tied together with rules

  target: prerequites
          action
          action
  

Automatic variables

Goal: Be more efficient with your time and with your rules

    column-utests: column-utests.o column.o 
            $(CC) $(CFLAGS) $(LDFLAGS) -o column-utests column-utests.o column.o

Goal: Make that target simpler (other than just using the default rle).

    LINK = $(CC) $(CFLAGS) $(LDFLAGS)
    column-utests: column-utests.o column.o 
            $(LINK) -o column-utests column-utests.o column.o

What happens if I want to change the target?

    cut: column-utests.o column.o 
            $(LINK) -o column-utests column-utests.o column.o

Whoops. I forgot to change it in the next line

Make includes default variables for

• target: $@
• prereqs: $^
• First prereq $<
• Prefix of target $*

• newer prerequisites ???

  cut: column-utests.o column.o 
          $(LINK) -o $@ $^
  

Generic rules

What if we have common rules for building certain things? Why copy/paste/change? With the percent sign wildcard.

    %.o: %.c

Another example: Document development

Let's say we start with Markdown. Markdown.pl translates a .md file to something like HTML.

That gives us incomplete HTML, we need to wrap it using wrap-md-html.

So, let's write rules.

Given a markdown file (.md) create a partial HTML file (.htm) using Markdown.pl

    file.htm: file.md
            Markdown.pl file.md > file.htm

Improved

    file.htm: file.md
            Markdown.pl $< > $@

How do I use other people's libraries

• Best answer: autoconf/automake figures it out for you
  • Hard to learn
• Traditional answer: Make user fill out a config file
• Intermediate answer: pkgconfig

Standard make rules

Other useful techniques

Miscellaneous tools and techniques

14:00:21 up 1004 days, 3:56, 2 users, load average: 11.95, 4.28, 3.89 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT root tty1 - 17Feb14 9days 1.90s 1.90s -bash root tty3 - 24Feb14 44days 0.02s 0.01s -bash