Introduction to Linux/UNIX

History UNIX beginnings in 1969 (Linus Torvalds is born!) AT & T Bell Laboratories (Ken Thompson & Dennis Richie) Working version (in 1970) on a DEC PDP 11/70 UNIX and C Relationship June 81: Berkeley UNIX 4.1 BSD (enhanced with vi, csh, and virtual memory management) 1983: Berkeley UNIX 4.2 BSD (added TCP/IP networking, sockets and a new file system) Later  UNIX/32V, SYSTEM III, SYSTEM V and  Linux is introduced by Linus B. Torvalds in 1991

GNU Project Launched in 1984 to develop a complete UNIX-like Operating System that is free software Organized by free software foundation Free GNU Software: Usually C code, but some C++ The GNU System provides a collection of applications, libraries, and developer tools, plus a program to allocate resources and talk to the hardware, known as a kernel

Basics Talking to Linux/UNIX  The Shell –displays the prompt for your next command –parses your command input and executes it –several different kinds: Bourne Shell or sh, ksh, csh, and tcsh Setup your environment variables:.bashrc Home directory /user/local/home/YourLoginName Your files are at: /user/local/home/YourLoginName/SDRIVE File/Directory structure  A tree

Useful UNIX/Linux Commands A subset of these commands are: alias/unalias, bg, cat, cc, cd, chmod, cp, csh, diff, du echo, emacs, fg, gcc, grep, history, jobs, kill, ln, logout lpq, lpr, lprm, ls, man, mkdir, more, mv, printenv, ps pwd, rlogin, rm, rmdir, rsh, script, set, setenv, source tail, tar, telnet, touch, unsetenv, vi, wc, which, xterm

More Basics … Consulting the on-line manual  man command Compiling with “gcc” and “g++” I/O Redirection > Redirect output < Redirect input p & Run p in the background (try also jobs, ^Z, bg, fg, ps, and kill) p1 | p2 Pipe output of p1 as input for p2 p >> f Append output of p into file f

Command-line arguments linux01 > myprog filename int main( int argc, char* argv[]) { } argv Myprog \0 filename \0 NULL argc = Text Editing / data compression GNU emacs (/usr/bin/emacs) vi (/usr/bin/vim) /bin/gzip /bin/gunzip

Writing Simple Shell Scripts Bourne Shell Programming (bash – standard Linux shell) Example: #!/usr/bin/env bash echo name of script is $0 echo first argument is $1 echo second argument is $2 echo third argument is $3 echo eleventh argument is $11 echo number of arguments is $#

More examples… Example 1: Remove "Cntl-M" from a given file Example 2: Keep track of users every 20 seconds Example 3: List all files in all subdirectories recursively Example 4: List and count all files in all subdirectories

Linux/UNIX Processes ps –acefl | more ps –acefl | grep “init” the first, primordial process  init PID=1 PPID=0 (kernel) All other processes are descendants of init. Each process has only one parent but could have many children Child processes inherit the environment of the parent process All programs start with three files open: stdin, stdout, stderr

Linux/UNIX Process Model Process Attributes A unique process identifier (PID) - getpid() call parent process (PPID) – getppid() call permission identifiers (UID, GID etc.) An address space A current working directory (.) A set of open files, directories environment variables – env or printenv (e.g. PATH= …; HOME=…) scheduling priority

make facility used for maintaining component modules in a software system. The default file for make is called makefile or Makefile. Otherwise, use “make –f filename” A makefile consists of a series of sections each composed of target, dependencies and commands. Example : Every command line must begin with a tab. make target returns without doing anything if no changes are made to any of the files involved in making the target.

makefile #A simple Makefile example default: all all: driver driver: program.o \ "Building g++ program.o scanner.o -o driver program.o: parser.h symbol.h \ program.cpp g++ -c program.cpp scanner.o: scanner.h \ scanner.cpp g++ -c scanner.cpp clean : rm driver program.o scanner.o