Compiling and Using UNIX

Last time: Emacs

Prof. Brian D. Davison

Computer Science & Engineering, Lehigh University

Development Process

• In C, we use the same design, edit, compile, execute process as any other language, or development platform -- just the tools are different.
• Use gcc -o prog file.c instead of the a.out from our first example
• When compiling multiple files, use multiple steps
  
  % gcc -c file.c
  % gcc -c file2.c
  % gcc -o prog file.o file2.o

Makefiles

• Normally we automate all of this with a Makefile, such as:
  
  prog: file.o file2.o
  <TAB>gcc -o prog file.o file2.o
  
  file.o: file.c
  <TAB>gcc -c file.c
  
  file2.o: file2.c
  <TAB>gcc -c file2.c

Better Makefiles

CC=gcc
CFLAGS=-O2 -g -Wall
LFLAGS=-g -Wall

prog: file.o file2.o
     ${CC} ${LFLAGS} -o prog file.o file2.o

file.o: file.c
     ${CC} ${CFLAGS} -c file.c

file2.o: file2.c
     ${CC} ${CFLAGS} -c file2.c

clean:
     rm -f *.o
     rm -f prog

Compiling under Emacs

• M-x compile -- Opens a second window within emacs, asks for compile command


• C-x ` -- Goes to the next line reported to have an error

Using UNIX

• Reminder: How to find information about UNIX commands/utilities:
• Type man <program> for any system command, most utilities
• Type info <program> for any GNU utility or program (and man pages!)
• Check your reference books
• The rest: Google, TA, instructor, etc.
• What if you don't know the name of the program?
• man -k <keyword>
• also check your text (UNIX in a Nutshell)

Logging in and out

• Use ssh instead of telnet (even when permitted, as ssh is more secure)
• Use your ssh client to connect to a CSE/ECE Sun
• On our Suns (and Linux) your default shell will be bash (Bourne-Again Shell). Modern shells, including bash, offer:
  • tab completion -- just type the first few letters and press tab to complete the command name
  • command history -- use the up and down arrows to select from your history of past commands
  • emacs-like keybindings -- C-a, C-e, C-t, C-b, C-f, C-p, C-n all same
• When complete, type exit. Some shells will also allow CTRL-D (EOF) to signal the end of the session.

Comparison to DOS/Windows

• Some ideas are similar, such as a file structure of nested folders
• Differences
• UNIX filenames are case-sensitive, so "hello.txt" and "Hello.txt" are not the same.
• UNIX pathnames use a slash (/) as a separator, not a backslash (\) as in DOS/Windows. The backslash is used to escape special characters just like in most programming languages.
• UNIX has no "drive names" like A, C, D. Instead, the entire filesystem is mapped under a single root directory "/"
• Often the current directory is not in user's path by default. Need, for example, ./progname
• All files and directories belong to some user, and have access permissions.
• There is a special "root" account for system administration (separate from regular users), which can read and write essentially anything, anywhere, regardless of access permissions.

UNIX Commands 1

• Where are you?
tritan 2% pwd
/home/brian/WWW-data/course/cunix
• Who are you?
io:~% whoami
bdd3
• Moving to another directory
io:~% cd cse271.071/
io:~/cse271.071% cd ..
io:~% pwd
/home/bdd3
io:~% cd .
io:~% cd ~
io:~% cd /home/bdd3
io:~%

UNIX Commands 2

• List directory contents
io:~/cse271.071% ls
hw1/
io:~/cse271.071% ls -l
total 2
drwxr-xr-x 2 bdd3 ugrad 512 Jan 19 01:16 hw1/
io:~/cse271.071% ls ..
Desktop/ cse271.071/ nsmail/ test.c
Mail/ mail/ test* test.c~

• Deleting files
% rm test
% rm -rf /mail

Viewing Files

tritan 2% cat -n test.c
1 int a;
2 int main (sdfsdf a)
3 {
4 int b;
5 }
tritan 2%

C Programming

• There are many more useful UNIX utilities that we will discuss in the future, but let's consider building one.
• We just saw that cat can display the contents of a file.
• Let's write our own version in class. Since cat reads from files, we'll need to use the open(2), read(2), and close(2) system calls.
• Note that the man system also has entries for system calls and standard library functions as well as for programs.

Looking Ahead

• HW1 is due tonight.
• Monday we will be in PL502, going through some exercises on using UNIX and simple C development.