CSCI 1730 April 1 st, 2014

Materials Class notes slides & some “plain old” html & source code examples linked from course calendar board notes & diagrams Textbook (Hoover) Buy new / buy used / rent / eTextbook

Text System Programming with C and Unix by Hoover Ch 1: Introduction Ch 2: Bits, Bytes and Data Types Ch 3: Arrays and Strings Ch 4: Pointers and Structures Ch 5: Input/Output Ch 6: Program Management Ch 7: System Calls Ch 8: Libraries Ch 9: Scripting Languages

The UNIX operating system kernel + shell + system calls kernel: provides access to H/W resources of computer manages memory and CPU shell: provides command-line interface to services system calls: provide method-call interface to services

Overview of UNIX portion of course We'll (try to) cover: basic concepts and terminology files and directories processes interprocess communication signals and signal handling pipes shared memory, messages, semaphores X terminal i/o sockets standard i/o library

Basics: Files and Processes info stored in files while files have logical structure to programs that create and use them, at the UNIX level they are just a sequence of bytes no record terminators, no file terminators, no special file types names < 256 characters < 14 to be backward compatible

Directories, pathnames directories have hierarchical, tree-like structure each directory can contain files and subdirectories full names of UNIX files are pathnames, including directories /users/faculty/eileen/junk.txt /users Faculty eileen junk.txt … … …

Example /users/faculty/eileen/junk.txt (absolute pathname) if _current working directory_ is /users/faculty/eileen can use junk.txt (relative pathname) if _current working directory_ is /users/faculty can use eileen/junk.txt (also a relative pathname)

Ownership, permissions each file has an owner that owner is a member of a _group_ each file has 3 sets of permissions: read/write/execute one set for owner, one set for group, one set for public -rwxr-xr-x. 1 eileen users 50 Mar 31 20:29 play.exe -rw-r--r--. 1 eileen users 50 Mar 31 20:28 junk3.txt -rw-r eileen users 50 Mar 31 20:28 junk2.txt

Devices UNIX treats devices like files. filenames exist that represent devices like a keyboard or printer. To write to the printer, you can just write to the file that represents it... for example cat fileX > /dev/rmt0 causes the contents of fileX to be written to the tape drive associated with the rmt0 file in the /dev directory

Processes process = instance of an executing program When you type: > ls at the command line, the shell process creates a process to run the ls program. UNIX is multitasking more than one process can run at the same time i.e., multiple processes share the CPU

IPC: Interprocess Communication Consists of mechanisms that allow processes to send info to one another Methods differ in : type/amount of info number of processes whether processes need to exist at the same time whether processes need to be on the same machine

IPC: InterProcess Communication pipes output of one program is input of another signals processes that exist at same time on same machine can send integer signals shared memory processes that exist at same time can share variables semaphores control access to shared memory sockets processes that exist at the same time on same or different machines can communicate arbitrary info

The shell supports pipes: >ls | more output of the ls program is input to the more program >ls | grep notes | more output of the ls program is input to the grep program notes is a command line parameter to output of grep is input to more

System calls and library functions kernel memory resident program, deals with process scheduling and i/o control system calls the interface to the kernel and the resources it controls. invoked like library subroutines (but typically more efficient, lower level, run in 'kernel mode' rather than 'user mode'). Library routines are a layer between user code and system calls.

Common shell commands cd pwd set which

Common system commands grep ls man more time sort

C review – 4 data types /* A review of the basic data types in C. */ #include int main() { intx,y; chara; floatf,e; doubled; x=4; y=7; a='H'; f=-3.4; d= ; e= ; printf("%d %c %f %lf\n",x,a,e,d); printf("%d %c %.9f %.9lf\n",x,a,e,d); }

C review – arithmetic /* A review of the basic arithmetic operators in C. */ #include int main() { int x,y; int r1,r2,r3,r4,r5; x=4; y=7; r1=x+y; r2=x-y; r3=x/y; r4=x*y; printf("%d %d %d %d\n",r1,r2,r3,r4); r3++; r4--; r5=r4%r1; printf("%d %d %d\n",r3,r4,r5); }

C review – loops #include /* A review of the loop types in C. */ int main() { int i,x; x=0; for (i=0; i<4; i++) { x=x+i; printf("%d\n",x); } while (i<7) { x=x+i; i++; printf("%d\n",x); } do { x=x+i; i++; printf("%d\n",x); } while (i<9); }

C review – blocks /* A review of conditionals and blocks in C. */ #include int main() { int i,x; x=0; for (i=0; i<5; i++) { if (i%2 == 0 || i == 1) x=x+i; else x=x-i; printf("%d\n",x); }

C review – flow control /* A review of flow control statements in C. */ #include int main() { int i,x; x=0; for (i=0; i<5; i++) { if (i%2 == 0) continue; x=x-i; if (i%4 == 0) break; printf("%d\n",x); }

Chapter 2

ASCII /* This program shows the dual interpretations of char and ** unsigned char data types. */ #include main() { char a; unsigned char b; a='A'; b='B'; printf("%c %c %d %d\n",a,b,a,b); a=183; b=255; printf("%d %d\n",a,b); }

sizeof() operator /* This program demonstrates the sizeof() operator. */ #include main() { int i; char c; double d; printf("%d %d %d %d\n",sizeof(i),sizeof(c),sizeof(d),sizeof(float)); }

Bitwise NOT /* This program demonstrates the bitwise not operator. */ #include main() { unsigned char a; a=17; a=~a; printf("%d\n",a); }

Bitwise AND /* This program demonstrates the bitwise and operator. */ #include main() { unsigned char a,b; a=17; b=22; a=a & b; printf("%d\n",a); }

Bitwise OR /* This program demonstrates the bitwise or operator. */ #include main() { unsigned char a,b; a=17; b=22; a=a | b; printf("%d\n",a); }

Bit operators (variables and constants) /* This program demonstrates using the bitwise operators ** with variables and constants. */ #include main() { char x,y; x=7; y=6; x=x&y; y=x|16; printf("%d %d\n",x,y); }