CSC295 2014S, Class 10: Improved Make
=====================================

_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