• 1. The UNIX Operating System
  • 2. UNIX Operating SystemObjectives : Learn about the Unix Operating System and develop the skills required to build software applications in the Unix Environment.
  • 3. 1. Introduction & History of UNIX 2. File System 3. Basic Utilities 4. Shell Features 5. Advanced Utilities 6. Communication Features 7. System CallsContents :
  • 4. Chapter 1 Introduction and History of UNIX
  • 5. Introduction and History of UNIX 1. Evolution 2. Development 3. Standard release- AT&T versions 4. BSD UNIX 5. Other implementations of UNIX 6. Features of UNIX 7. UNIX Philosophy 8. UNIX operating system 9. UNIX Kernel 10. Programming Environment 11. Design Principles 12. Limitations
  • 6. Primarily influenced by MULTICS MULTICS - Developed for GENERAL ELECTRIC 645 mainframe computer - Interactive operating system - Batch - mode characteristics UNIX Operating System - First Version developed in 1969 by Ken Thompson on DEC PDP Series ( PDP - 7 ) - Business, Scientific and Industrial UsersEvolution
  • 7. Development * Originally written in assembly language for PDP-7 * Transportability facilitated by Thompson who developed the B language * B language modified by Ritchie and renamed as C language * Thompson (1980) and others wrote UNIX in C which could be ported to any computer
  • 8. Standard release - AT&T Versions Version 3 • Written in C • Moved to PDP - 11/45 and PDP - 11/70 Version 6 • Released in 1975 • For use by universities only Version 7 • Released in 1978 • First commercial version but primarly used in universities • 32V - VAX version Version 8 • UNIX Support Group(USG) takes responsibility • Research Group still busy
  • 9. Standard release - AT&T Versions …Contd... System III • Released in 1981 • Commercial orientation • Over 100 manufacturers of UNIX-based micro , mini and mainframes • UNIX users > 100,000 System V Release 1 • Released in 1983 • Enhancement of System III System V Release 2 • Released in 1984 • Enhancements of System V , Release 1 System V Release 3 • Released in 1988 System V Release 4.0 •
  • 10. BSD UNIX (from Berkeley Software Distributions) * UNIX's entry into University of California, Berkeley Campus during 1976-77 * Inputs of UCB Faculty/researchers incorporated in System V of AT&T UNIX UNIX 3BSD • Released in 1978 • Developed by Bill Joy and Ozalp Baboglu • Added Virtual memory, Demand paging to the VAX version 32V UNIX 4BSD • DARPA - funded Development • Provided support for DARPA TCP/IP • C-Shell , ex/vi , new compilers for PASCAL and LISP were added UNIX 4.1 BSD • Released in 1981 UNIX 4.2 BSD • Released in 1983 UNIX 4.3 BSD • Latest Release
  • 11. Other Implementations of UNIX (based on Version 7, System III, System V of AT&T UNIX or UNIX 4.2 BSD) Xenix Microsoft’s UNIX operating system to run on microcomputers IBM PC/IX IBM PC Zeus Zilog Computers DEC Ultrix DEC HP-UX HP UNIX SUN Elxsi UNIX ELXSI Pyramid UNIX Pyramid Data General UNIX Data General Perkin Elmer UNIX Perkin Elmer MassComp UNIX Mass Computers NBI UNIX NBI Amdahl UNIX Amdahl
  • 12. Multitasking Performing tasks simultaneously rather than sequentially e.g., While printing a document , start editing another document Each task is considered to be a process Multi-user Several users can use the same computer simultaneously i.e , more than one keyboard and terminal can be connected to one computer Highly cost-effective Portability Easier to modify the UNIX system code for installation on a new computer rather than write from scratch a new operating system UNIX Features
  • 13. UNIX System supplied tools Integral utilities Basic Operation of Operating system like Command interpreter or Shell Tools Text print formatting like nroff and typesetting troffUNIX Features
  • 14. * Available on micros, minis and mainframes * UNIX Communication and electronic mail • Communication between different terminals hooked to same computer • Communication between computers of different sizes and types in different locations as far away as other countries * Incorporation of third party application programs * Hierarchical File System * On-Line Help facility Example : man * Library of application software
  • 15. Make each program do one thing well Expect the output of one program to become the input to another Suited for prototype development i.e., design and build easily Modular approach i.e., be prepared to throw and rebuild Usage of tools Building essential tools The UNIX Philosophy
  • 16. Kernel Schedules tasks and manages data storage Shell A program that • interprets the user commands/requests • calls programs from memory and • executes them one at a time or in a series (called a pipe) Tools & Specific capabilities added on to the OS Applications Kernel( Heart of Unix Operating System) Shell Interpreter Tools and ApplicationsThe UNIX Operating System
  • 17. The Users Shells and Commands Compilers and Interpreters System Libraries System Call Interface to Kernel Signal File System CPU Scheduling Terminal Swapping Page Handling Replacement Character Block Demand Paging I/O System I/O System Terminal Disk & Tape Virtual Drivers Drivers Memory Kernel Interface to the Hardware Terminal Device Memory Controller Controller Controller Terminals Disks & Tapes Physical Memory
  • 18. File Management And SecurityNetworking ServicesDate and Time ServicesInput / Output ServicesSignal HandlingProcess Scheduling System Administration and AccountingMemory ManagementUNIX SYSTEM KERNELThe UNIX Kernel
  • 19. * A GOOD operating system !! • Simple yet powerful • Allows building of tools, writing of small programs and putting them together • A rich & productive environment * A PORTABLE operating system !! • Written in C • Runs on a range of computers • Source code is available The Programming Environment
  • 20. * Designed for Programmers * Interactive * Multiple Processes can be initiated Foreground Process Background Process * Methods to Co-ordinate Process * Signal to communicate with processes * Files, Directories, Devices treated as files * Tree structured directories to hold files * Emphasis on program development facilities * Sources available on-line * Simplicity before efficiencyThe Design Principles
  • 21. * Designed for computer professionals * Not a real-time operating system * File Security depends on owner * Defective programs may keep runningDrawbacks of UNIX
  • 22. Chapter 2 File System
  • 23. 1. File System Layout 2. Concepts of file 3. Features of File system 4. Starting and Ending a session 5. File Management utilities 6. Directory Management 7. File operation 8. Mountable File System 9. File security The UNIX File System
  • 24. Disks are partitioned into File Systems. - Logical blocks of 512 bytes or multiples - Arranged to form a hierarchical structure - Convenient to manage data File System Layout Boot Super Inode Data block block list block Boot block - generally occupies the first sector - may contain bootstrap code Super block - Information about the file system How large, where free and other details Inode list - Contains a list of inodes - One inode is the root inode Data block - Contains file and administrative data - Allocated data can belong to that block only File Systems in UNIX
  • 25. - Ordinary Files - Directory Files - Special Files - Standard Files Classification of files in UNIX
  • 26. * A File in UNIX is a Stream of bytes ( 8-bits) Kernel does not impose a structure on files * File may contain text, data and even machine language code Examples Text Files : Lines of ASCII characters separated by a new-line Commands : Sequence of commands interpreted by UNIX text Data : File containing data as stream of bytes Executable : File containing machine language instructions * The files format remains unchanged but only the way the program interprets it is different Concept of Ordinary Files
  • 27. * Gathering together related files in a common place * Every file is assigned to a Directory * Directories have names (maximum of 14 characters) * A file within a Directory can itself be another Directory (A Sub-directory) * Internally a Directory is just a file that contains - a list of file names - their Inode Numbers and - a pointer to the actual file on the disk * An upper limit of around 35 sub -directories Examples / ( Forward slash ) Prime or Root Directory Note - in DOS it is \ ( Backward slash ) /usr Directory for the user /usr/trg1 Sub-Directory for trg1 under Directory usr Concept of Directory Files
  • 28. * Used to reference Physical devices such as terminals, disks, floppy drives and tape drives * Read and written like ordinary files * Requests cause activation of the associated Physical Device * Device Drivers associated with each file * Types : Character file Terminal (tty0, tty1 ) Transmits data Character by Character Block file Disk Drives (hd0,fd0) Transmits data in 512 or 1024 byte chunks * Major and Minor numbers identify the hardware link Major No.s : Indicates type of device Minor No.s : Different instances of the device Concept of Special Files
  • 29. * Helps display information on the screen * Special Names for Communication channels * Keyboard input channel is called Standard input (stdin) - file id is 0 * Terminal Screen output is called Standard output (stdout) - file id is 1 Diagnostic error messages (generated by a program) are sent to Standard error (stderr) - file id is 2 ( shown on terminal screen ) * All three files are open by default at the time of loginConcept of Standard Files
  • 30. * A means for the system to identify a file Note : Unix is case sensitive * User accesses a file by a user-assigned file name * Can be a sequence of characters (a maximum of 14 ) * May be identified by two or more names (Multiple links to a file) * Internally assigned a unique inode number (for a File System) * Different files can be grouped under a directoryFile Names
  • 31. Absolute Path name * A file is identified by the path name from the root e.g., /usr/trg/c/test.c where • test.c is an ordinary file • usr, trg, c are directories • trg is a sub-directory under usr Relative path name * UNIX keeps track of the user's current directory * If a "/" does not precede a file name then the name interpretation begins with the current directory e.g., If current directory is /usr/trg then the file could be just referenced as c/test.c Path Names
  • 32. * Hierarchical * Security on each file - Owner - Group - All others * Separate security for - read - write and - execute * Removable * File Independence - * Time stamp on each file - Modification time - Access timeFeatures
  • 33. devbinlibspooletctmpconsolelp0tty0shcsh------Libc.agroupinit---passwd/spelltroff---man---localuchbinsrclibtmp------trofftmac---libbin*.hincludeusrUnix
  • 34. /bin Basic Unix utilities cp, mv, ln /dev Special I/O device files fd0, lp0 /etc Administrative Programs passwd, shutdown /lib Libraries used by Unix libc.a /usr/bin Unix utilities cal, bc,spell /usr/adm Administrative commands and files adduser /tmp Temporary files created on error conditions Standard File Hierarchy
  • 35. /usr/games - Game Programs /usr/include - Include files for language procedure Examples : C-header files stdio.h, math.h /usr/lib - Archive libraries Example : troff /usr/mail - Mail files Example : mailbox /usr/news - News files /usr/spool - Spool files /usr/tmp - Temporary files /usr/src - Program Source Files
  • 36. * Three levels of access User/Owner, group, others * Three types of access on Files and Directories Read, Write, Execute Access Mode Ordinary Directory Read Examination of Listing of File Contents files within Directory Write Allows changing Creating new of file contents files within Directory Execute Executing file as Searching the a command Directory allowed allowed Security and Access Methods
  • 37. login : User can type his name and password to identify himself login command can be used as $ exec login to log-on onto another user account after identifying yourself in response to prompts for user name and password su setuser This is used to become another user or super-user provided the password is known. e.g., $su Prompt the user for the superuser password $su - trg2 Prompt the user for the password of user trg2 $su - trg2 -c "ls -l" Temporarily changes to trg2 and executes the command ls -l and comes back to the original userStarting and Ending a Session
  • 38. Starting And Ending A Session …Contd…. passwd Change the password for the user e.g., $ passwd Prompt you for old password and new password logout This command exits or logs-out from the current user and executes the file .logout before coming out e.g., $ logout or $ exit or $ exits from the current login
  • 39. Directory Operation File Comp. Security Management cd cmp passwd pwd comm crypt mkdir chown rmdir chgrp mvdir umask chmod File File Mountable Copy, Move contents compression file Remove & Time cat pack mount cp ls unpack umount ln wc mv file rm touchFile Management Utilities
  • 40. mkdir creates a new directory rm removes a file rmdir removes a directory du displays disk usage df displays number of free block touch updates the time of last modification find locates files that match certain area file displays the type of file pwd displays full pathname of current directory
  • 41. General Structure: Command Name [Options] [Arguments] E.g.,Command Name Tells the shell what to do (in this case list files)Options Control how the command will work (in this case ask for a long listing)Arguments on which the command works (in this case the directory usr/trg )ls-l/usr/trgCommand Structure
  • 42. Directory Management cd Change working Directory cd.. Parent Directory cd. Current Directory e.g., $ cd /usr/trg/c ( current Directory is c ) $ cd .. ( current Directory is trg ) $ cd ./c ( current Directory is again c ) or $ cd c $ cd ( home directory - in this case /usr/trg) mkdir Make a Directory $ mkdir pathname Makes Directory in 777 mode Write permission should at least be permitted for owner in parent Directory e.g., $ mkdir /usr/trg2 ( makes directory trg2 )
  • 43. rmdir Remove a Directory $ rmdir pathname * Directory should be empty, or else rm -r (recursively remove) e.g., $ rmdir /usr/trg2 (removes directory trg2) pwd Print Working Directory
  • 44. cat Concatenate & Print on screen or printer $cat [Options] [Arguments] Options - take input from stdin -n no. of output lines -s squeeze adj. blank lines -v enable display of non-printing characters -b used with -n to avoid numbering blank lines e.g., $ cat try.c Display the contents of try.c on the screen $ cat Takes input from stdin i.e. keyboard and displays on screen File Contents
  • 45. $ cat f1 > f2 Takes input from file f1 & puts it on file f2 $ cat f2 > f3 f3 contains the contents of f1 $ cat f4 >> f3 Appends the contents of f4 to file f3 $ cat try[0-3] > final The file final contains contents of try0, try1, try2 try3 $ cat test* > report The file report contains all files beginning with test
  • 46. Is[Options] List the Directory Contents Options -1 number one single column output -l long format (II also used) -a all entries including dot files -s gives no. of disk blocks -i inode no. -t ordered by modification time recent first recursively display all directories, starting specified or current directory
  • 47. $ Is -I List the files along with the protection bits and the user $ Is -a List the files starting with .and..also $ Is -1 symtab.c symtab.o treegen test $ Is -I -rw-r—r— 1 smj proj1 30766 Mar 3 15:08 symtab.c -rw-r—r— 1 smj proj1 8759 Mar 3 15:12 symtab.o -rwxr-xr-x 4 smj proj1 40743 Mar 3 15:23 treegen drwxrwxr-x 1 smj proj1 53 Mar 1 09:15 test $ Is -a . .. .profile .cshrc symtab.c ... $ Is -iI 10936-rw-r—r—I smj proj1 3076 Mar 3 15:08 test.c 10936 - inode number of file test.c
  • 48. wc Word Count $wc [Options] filename Options - Display no. of lines, words, characters -I Display no. of lines -w Display no. of words -c Display no. of characters e.g., $ wc test.c 20 200 5678 20 - lines 200 - words 5678- characters nl no. of lines in the file and temp’ly lists out the file Similar to wc -l < filename >
  • 49. file Determine file types $file [Options] [Arguments] Options -f filelist Normal File Types - C program text - assembler program text - commands text - ASCII text - English text e.g., $ file test.c C Program test
  • 50. cp copy a file -i - user interactive mode e.g., $ cp test.c test.c.bak test.c and test.c.bak contain the same contents Extra disk storage In Create link e.g., $ ln first.c second.c The file is referenced by two different names No Extra disk storage
  • 51. mv Moves or renames files and directories -i interactive mode e.g., $ mv old.c new.c Renames the file old.c as new.c rm Deletes the indicated file(s) files rm removes files and directories -i remove interactively -f forcible remove -r remove recursively • Dangerous • used in conjunction with -i touch Updates access, modification or change times of a file -a update access time -m update modification time -c prevents creating the file e.g., $ touch f1 * The current system date & time stamp is put on the file f1 * If f1 does not exist then it is created with 0 bytes
  • 52. cmp Compare two files If files are same no output is sent to the terminal, or else The line number and the byte at which the first difference occurs is reported -s Outputs nothing Registers return code Return code 0 if files are identical 1 if files are different 2 on error e.g., $ cmp test1 test2 test1 and test2 differ in char 36 line 3 $ cmp -s test1 test2 $ echo $status outputs 1 indicating that the files are differentFile Comparison
  • 53. diff - Reports more than one differences $diff [Options] file1 file2 -b Ignores trailing blanks -e Gives a list of ed commands so as to convert file1 into file2. e.g., $ diff test1 test2 Outputs: n1 a n3,n4 n1,n2 d n3 n1,n1 c n3,n4 where * n1 ,n2, n3 ,n4 are line numbers * a ,d, c means append, delete ,change respectively
  • 54. comm Display common lines $comm -[123] f1 f2 Prints a three column output: - lines that occur only in f1 - lines that occur only in f2 - lines that occur in both comm -12 - prints lines common to the two files comm -23 - prints only lines in the first file but not in the second comm -123 - prints nothing e.g., $ comm test1 test2 Reports the common lines between files test1, test2 and reports the lines differing $ comm -12 test1 test2 Prints line common to both
  • 55. pack Compress the file $ pack e.g., $ pack try - Creates a file try.z which is packed - Normally the executables are packed - The size is reduced by 25 - 40 % unpack Uncompress packed file or pcat e.g., $ unpack try.z or $ pcat try.z unpacks the file try.zFile Compression
  • 56. mount Associates a directory with a device e.g., Mounting a floppy on the root file system umount Dissociates directory from the device e.g., $ mount /dev/fd096 /mnt Mounts the floppy on the directory /mnt $ umount /mnt Dissociates /mnt from the floppyMountable File System
  • 57. passwd To change the password chown To change the ownership of the file $ chown owner filename e.g., $ chown trg2 test.c * Initially the owner is trg1 * Only the owner or the superuser can change the ownership of the fileFile Security
  • 58. chmod change the permissions of the file $ chmod who op permission who a, u, g, o all, user, group, others op +, -, = + add, - remove, = set permission r,w,x r read, w write, x execute e.g., $ chmod a=rw test.c * users, group, others have read and write permissions $ chmod u+r, g+w, o+x test.c * read for users write for groups execute for others $ chmod 777 test.c * Sets read, write, execute Permissions
  • 59. umask Set file creation mode mask $ umask nnn (nnn set file creation mode) umask can also be set as a shell variable e.g., umask 022 - Files normally created with 777 mode is assigned 755 permission The value of each digit is subtracted from the corresponding "digit" specified by the system for the creation of a file.
  • 60. tail Displays the last lines of file options : -n (n= no. of lines) e.g., $ tail -30 test.c Displays the last 30 lines of file test. c head Displays the top lines of file e.g., $ head -10 test.c Displays the first 10 lines of test.c split Splits the file into different files as specified by the number of lines e.g., $ split -20 test.c Splits the file test.c in blocks of 20 lines and creates files xaa, xab, xac and so on, such that xaa has first 20 lines of test.c xab has the next 20 lines of test.c ... The file test.c is unaffected $ split-20 test.c try Generates files as tryaa , tryab , tryac paste Joins the two or more files horizontally e.g., $ paste xaa xab File xaa and xab are joined horizontally and output to the terminalFile Operation
  • 61. Chapter 3 BASIC UTILITIES
  • 62. 1. Line Editor Ed 2. Visual Editor Vi 3. Debuggers 4. Profiling Tools 5. C-BeautificationBasic Utilities
  • 63. Invoking ed: $ ed filename Prompt : Ed has no formal prompt P - Prompts with a “*” This is a toggle function Append: a - Appends given text after current line Write : w - Writing to the file Exiting ed : q - Quit from ed Example : $ ed test.c ? test.c P *a <————> <————> <————> *w *q The edit buffer can be written to some other file also as *w filenameThe Line Editor - ed
  • 64. abc abc a*bc abc, aabc, aaa...bc a.c abc, aac, acc, axc, a$c a.*c abc, axyc, a$+pmc, abcdefgc a[b2m]c abc, a2c, amc a[0-2b-d]c a0c, a1c, a2c, abc, acc, adc a[^0-2]c a3c, a5c, axc, .... a[xy]*c ac, axc, axxc, ayyyc a\{3,\} aaa, aaaa - 3 or more a’s a\{3,5\} aaa, aaaa, aaaaa between 3 & 5 a’sPattern Matching
  • 65. Command Explanation Usage p print current line (s) 1,3p l list current line(s) 2,4l (display invisible characters like tabs etc.) n print line(s) with number before it 1,5n a append text after current line 4a i insert text before current line 3i Adding and Replacing Text..
  • 66. Command Explanation Examples . Pointer to current line * - Previous line .= Gives line number n Current line is ‘n’ * - Current line +n Move up by n lines -n Move down by n lines $ points to the last line , short for 1,$ ; short for .,$ /.../ forward search for string of characters enclosed between slashes*$= Prints total no. lines but does not changecurrent line Traversing within a file
  • 67. Command Explanation Usage d delete line(s) in text 2,5d c change line(s) in text 2,4c m move line(s) in text 2,3m5 t copy line(s) in text 2,3t5 j join lines in text 2,3j u undo last command Note : The above commands can be easily remembered by associating them with the first characters of their action. Substitute Commands (n,n)s/oldstr/newstr - replaces oldstr with newstr (n,n) range of lines - optional s/oldstr/newstr/g - all oldstrs' on the current line are replaced with newstr s/oldstr/newstr/p - the replacement is only effected in print but not executed s/oldstr/newstr&/ - newstr is inserted at every match s/oldstr/%/ - matched strings are replaced by the replacement string in the most recent substitute command Modifying Text
  • 68. /^ pattern/ searches for patterns at beginning of line /pattern $/ searches for pattern at end of line /pattern/ the pattern is searched forward // forward search ?? backward searchFinding Text
  • 69. Command Explanation (n,n)g/findstr/commandlist Executes given commandlist for every occurrence of findstr (n,n)G/findstr/ Inputs one command to execute for every occurrence of findstr (n,n)v/findstr/commandlist Executes given commandlist for every non-occurrence of findstr (n,n)V/findstr/ Inputs one command to execute for every non-occurrence of findstr Command Execution
  • 70. Command Explanation f print current filename w write contents of buffer into file w file2 write contents of buffer to file 2 r read current file after current line r file2 read contents of file2 after current line e file2 edit file2 —> invoke ed on file2 !shellcmd Execute shell command by preceding with ‘!’ ! ls –l gives a listing of current directory Special ed Commands
  • 71. * an improved version of ed * less terse * provides display options like numbered line * allows shorthand versions of commands * clear response for error messages The ex editor
  • 72. The editor * Powerful full screen editor * vi v/s ed, ex * Mostly single key stroke commands * Interface with ‘ex’ * Macro facility * Ability to process text Invoking $ vi filename e.g., $ vi pgm.c Modes : * Command mode * Insert mode * From Insert mode Pressing remitts Command modeThe vi - Visual Editor
  • 73. Types of commands * vi-commands (invisible) Command mode Commands can be categorised as : * Cursor movement * Text manipulations - insert, delete, copy, change * Marking/Selecting, Positioning * Search Objects of interest recognized by ‘vi’: * characters * words * lines * block
  • 74. Format of commands [count] command [operand] Use “.” to repeat last command Use “u” to undo last command Cursor Movement Line Oriented : ^ or (zero) beginning of line $ end of line Character oriented h move left l move right j move down k move up
  • 75. Format of commands (contd.) Word Oriented : e move to end of next word w move to beginning of word b move to beginning of previous word E move to end of next word ignoring punctuation W move to beginning of word ignoring punctuation B move to previous word ignoring punctuation
  • 76. Block Oriented : ) move forward one sentence ( move backward one sentence } move forward one para { move backward one para % move to find matching parenthesis Rightly used in C- Programming for matching ‘(‘ & ‘)’ m mark a particular line with a label. e.g., ma (marks the line with label a) “ return cursor to position (m) e.g., "a moves the cursor to the line which was marked with label a ^g file information, line number (Ctrl +g)
  • 77. Text Manipulation Insert mode : a append after cursor A at end of line i insert at cursor I at beginning of line o enter in new line after current line O enter in before current line esc to exit insert mode Delete mode : u undo last command nx delete n- next character ndw deleting n next words ndd deleting n lines - current line and n-1 below current line are deleted. D delete till end of line
  • 78. Changing Text : nr replace char s delete current char, enter insert mode S delete line, enter insert mode cw change word Cut & Paste : nyy yank n line Named Buffers : a to z ( 26 ) Unnamed Buffers : 1 p print buffer Join : J join next line to current EOL
  • 79. Search Searching for a character : fc search forward for character ‘c’ tc similar to f, cursor placed 1 char left of ‘c’ Fc search backward for character ‘c’ Tc similar to F, cursor place 1 char right of ‘c’ ; continue search in same direction ‘ continue search in reverse direction
  • 80. Search File Related : G go to the end line nG go to the nth line M go to the middle line H go to the top line L go to the last line
  • 81. Text Manipulation Screen Adjustments : ^d Scroll down half a screen ^u Scroll up half a screen ^f Page forward ^b Page backward ^e exposes one more line at bottom of screen ^y exposes one more line at the top of screen
  • 82. Text Manipulation Searching for a string : /string for searching forward ?string for searching backward Use n to continue search in the same direction Use N to continue search in the opposite direction s/oldstr/newstr commands can be used in vi
  • 83. Common Set commands :set ai Causes automatic indentation :set noai Nullifies the effect of auto-indent :set nu Causes line numbers to be displayed :set wrapmargin = n Sets n column right margin :set bf The beautify option Removes all unimportant control characters :set Causes a displays of current set options
  • 84. Text Manipulation :w! file force write :q quit normally :q! quit, no write :n next file, for $ vi f1 f2 f3 f4 :n! edit next file, discarding changes to current file :n args specify new argument list
  • 85. Why ? * for running a Program under the control of the programmer * for examining the values of various variables and stack contents Types fsdb File System Debugger Fixes damaged file system kdb Kernel Debugger Resides in kernel, Allows memory examination Disassembles instructions Executes programs sdb - Debugging source code written in C, Fortran 77 - Available on System V Role The functionality of any debugger is essentially the sameDebuggers :
  • 86. Debugger - sdb * Invoked as sdb e.g., $ cc -g test.c $ sdb a.out * sdb checks for the status of files * sdb gives warning messages if source files are not present or source files were modified after the object files * sdb gives a prompt * after invocation * some commands can be used to avail the important features of sdb
  • 87. SDB Commands Command Explanation *r run the program (arguments optional ) *s stepping through the instructions *20b setting a break point at line number 20 (Normally break points are set at function calls) */pattern searches for the pattern * b setting the break point at the function name \*B gives a list of break points\ *d deletes the break point at the specified line no. *D deletes all the break points
  • 88. sdb Commands (contd.) Command Explanation *S stepping over the function call *c continue upto the break point *variable name prints the value of variable active at that time *variable name/x prints the value of variable in hex *variable name/c prints the value of variable in character *variable name/o prints the value of variable in octal *variable name/s prints the value of variable in null terminated string *variable name/a character strings at the specified address *function:variable prints the value of the variable in the specified function
  • 89. sdb Commands (contd.) Command Explanation *p print the current line of the source *p print the corresponding line-no of the source * prints next 10 lines of source or data or instructions depending on the previous command *w prints a window of 10 lines of source or data or instructions around the current line * executes the previous command *! executes the shell command *k kills the debugger *q quits the debugger
  • 90. CTRACE - DebuggerDifferent from the conventional debuggers like sdb Works in the absence of a debugger Ctrace simulates the insertion of printf statements Programmer’s way of debugging is to insert printf statements at the required places Results in more printf statements than the program itself Ctrace also traces infinite loops
  • 91. CTRACE - Debugger (Contd .) * Invoked as ctrace [options] < source-file > traced-file options : -o print the variable in octal -x print the variable in hex -u print the variable in unsigned format -e print the variable in floating point format -f trace only the selected function names -v complement of option -f trace all functions except those specified in the list
  • 92. e.g., $ ctrace < test.c > ctest.c test.c - source file ctest.c - traced file Compile the traced file as $ cc ctest.c creates in a default file a.out Run the executable $ a.out arguments are optional Outputs the values of variables and statements as desired by the user
  • 93. PROF and GPROF * Improves efficiency and debugging * gprof is available in BSD versions * The program should have been compiled with -p option for prof and -g option for gprof * prof - refers default input file mon.out * gprof - refers default input file gmon.out * Gives an idea as to which function used up the maximum timePROFILING TOOLS :
  • 94. Example of prof $ cc -p test.c $ a.out $ prof a.out Generates an output like.... %time cumsecs seconds #calls msec/call name 91.2 9.34 9.34 20100 _func2 7.2 10.08 0.74 1 acnt 1.0 10.18 0.10 100 _func1 0.0 10.24 0.06 1 _main %time Percentage of time consumed by the function cumsecs Running sum or cumulative sum of the functions called seconds Seconds consumed by the function calls Number of times the function was invoked name Function name
  • 95. * Beautifies the C-program code * Indents all the statements * Improves readability * Invoked as $ cb < source-file > target-file e.g., $ cb < test.c > test1.c test.c - source file test1.c - Beautified version of test.cCB - C Beautification
  • 96. Chapter 4 Shell Features
  • 97. Shell Features 1. Various kind of shells 2. Shell commands 3. Shell Startup Dot files 4. Shell variables 5. C Shell 6. Test conditions 7. Shell programming - Bourne Shell 8. Shell programming - C ShellShell Features
  • 98. 1. Bourne Shell sh 2. C Shell csh 3. Korn Shell ksh 4. Restricted Shell rsh 5. Visual Shell vshVarious types of Shells :
  • 99. Simple commands using shell Metacharacters Exit status - return value 0 - Successful - return value > 0 - Failure Redirection Default input from Keyboard Default output on the Screen < - Read from a file > - Redirect it to a file >> - Append to a file n>&m - Merge output from file descriptor n with file descriptor m n<&m - Merge input from file descriptor n with file descriptor m where n and m are file descriptors for the stdin, stdout and stderr files Pipeline sequence of commands separated by |Shell Commands
  • 100. ; sequential execution & asynchronous execution && following list executed if preceding pipeline returns zero value || following list executed if preceding pipeline returns nonzero value * matches 0 or more characters ? matches any single character in filenames $var value of shell variable var var=variable assign variable to var
  • 101. # rest of the line is a comment ‘...‘ run command within backward quote ‘...’ treats ... literally “...” treats ... literally except for $ and ‘...‘ and \ e.g., $ (sleep 5 ; echo “The date is `date` “ ) & date The Output of the above command will be 6345 Wed Sep 23 10:20:45 EDT 1991 $The date is Wed Sep 23 10:20:50 EDT 1991
  • 102. PATH * If full path is given while executing the command, the command is executed from the path specified * Else it is searched in the Shell variable $PATH * Search order is defined by value of Shell variable Path e.g., PATH = :.:/usr/bin:/bin:
  • 103. Shell Startup Dot files * Helps in customizing UNIX System * Executes .profile for Bourne Shell when user logs on * Executes .login and .cshrc for C Shell when user logs on * Executes .logout for C Shell when user logs out from C-Shell * Keeps track of the history mechanism In C Shell through the .history
  • 104. Shell Variables User defined assignment : name = value e.g., (on Bourne shell) $ x=”Hello how are you” $ echo $x Hello how are you $ PATH=$PATH:/usr/games $ export PATH $ echo $PATH :.:/usr/bin:/bin:/usr/games:
  • 105. Positional Parameters e.g., shellscript arg1 arg2 $0 $1 $2
  • 106. Evaluation of Shell Variables * $var value of var ; nothing if undefined * ${var} same as $var ; useful if alphanumeric characters follow variable name - derefrencing variable e.g., $ var=hello $ varx=goodbye $ echo $var hello $ echo $varx goodbye $ echo ${var}x hellox
  • 107. * $ {var?message} If defined , $var Otherwise print message if message not defined print default message e.g., $ echo ${var?} hello $ echo ${junk?} junk : parameter not set $ echo ${junk?my message error} junk : my message error * ${var-thing} Value of var if defined , else use thing $var unaffected
  • 108. * ${var=thing} Value of var if defined ; otherwise thing $var is set to thing e.g., $ echo $ {junk-’Hi there’} Hi there $ echo ${junk?} junk : parameter not set $ echo $ {junk=’Hi there’} Hi there $ echo ${junk?} Hi there * $ {var+thing} If var defined then thing Otherwise nothing
  • 109. Command Environment * Variables & associated values e.g., export A * Export from parent to child shell * Vice-versa not trueShell 1Shell 2Export A
  • 110. Predefined Special Parameters $# number of positional parameters $? exit value of last command $$ process number of a process $* all the parameters $! process id of last command started with asynchronous execution i.e., &
  • 111. Variables Used by Bourne Shell in .profile CDPATH search path for cd HOME login dir PATH search path for commands PS1 primary system prompt PS2 secondary system prompt IFS internal field separator MAIL files containing mail messages TERM terminal type EXINIT list of set commands for vi
  • 112. * Developed by Bill Joy ( Berkeley University) * More helpful interaction * Permits shorthand repetition * Permits aliasing The C Shell
  • 113. The variables can be defined using a set for C-Shell variables e.g., (on - C shell) % set x=‘date‘ % echo $x Wed Sep 23 12:15:20 EDT 1991
  • 114. History - Records previous commands ! is used to execute previous command Command Format : ! [ ] - absolute !1 - relative !-3 - name !c expr !?su? - absolute 0, 1, ...n - range a - e - last $ - All arguments * - Substitute :s/trg1/trg - Print only :s/trg1/trg/p
  • 115. History Mechanism Keeps track of commands % history Lists previous commands % ^old^new Modify last command e.g., % cd /usr/trg/SRC % ^SRC^src % cd /usr/trg/src % !15 Run command 15 % !c Run previous command beginning with c
  • 116. Changing Commands :S/pattern/replacement e.g., % !cd:s/trg/trg1 cd /usr/trg1/src % !ls : p Prints the previous command beginning with ls but does not execute it
  • 117. Using Arguments !$ last argument !^ Begin argument !* All arguments !10:5-9 Arguments 5 to 9 for command 10 e.g., %ls !15:2-4
  • 118. Alias mechanism Short names for frequently-used long commands e.g., % alias cdms ‘cd /usr/man/man\!$’ % cdms 2 % pwd /usr/man/man2 % alias cd ‘cd \!*;set prompt=”`pwd`>”’ sets the prompt to the present working directory as and when cd is used to change the working directory.
  • 119. { } Attach filenames to common root %cp /usr/trg4/{ac,docs,test} . %cp/usr/trg4/ac . %cp /usr/trg4/docs . %cp /usr/trg4/test . %ls {/usr/bin,/bin}/{ls,more} /usr/bin/ls : not found /bin/ls /usr/bin/more /bin/more : not found Filename Grouping
  • 120. Using C - Shell e.g., % cc test.c % vi test.c % !c % a.out % !v % !c - o test % test % car /usr/trg2/document/report % !! : s/car/cat or % ^car ^cat
  • 121. Variables in .cshrc of C SHELL % set variable=value histchars : % set histchars=";," will thereafter use ; as execution character , as substitution character history : % set history=40 path: % set path=:.:/bin:/usr/bin: prompt : % set prompt=”\!>”
  • 122. Variables in .cshrc of C SHELL setenv used to make a variable as an environment variable so that whenever changes are made it is also reflected in the environment like TERM , DISPLAY is used % setenv TERM=AT386-M filec : file name completion % set filec : Predefined Its usage : % set variable % unset variable ignoreeof : To ignore all eof character ^D % set ignoreeof noclobber : Abandons all command using output redirection % set noclobber which destroys an existing file and appends to non-existing file
  • 123. TESTing Strings test - z $string String length equal to zero test - n $string String length not equal to zero test $str1 = $str2 str1 is equal to str2 test $str1 != $str2 str1 is not equal to str2 test $string string is not a null stringTest Conditions
  • 124. To algebraically compare variable values test $num1 -eq $num2 Other algebraic operators -ne, -gt -ge -lt, -le File related $ test -f file True if file exists and is an ordinary file $ test -r file True if file exists and is readable file $ test -w file True if file exists and is writable file $ test -s file True if file exists and has size greater than zero
  • 125. Control flows if command then commands [ elif commands ] ... [ else commands ] fi case word in, pattern) commands ;; pattern) commands ;; ... esacShell Programming - The Bourne Shell
  • 126. for name [ in word ...] do commands done while command do commands done until command do commands done
  • 127. break n exit from for / while / until from level n continue n next iteration of for / while / until from level n exit n exit with value export [name..] export test expr evaluate conditions read [arg] read variables from stdin or Keyboard shift n shift positioned parameters w.r.t $1
  • 128. Examples $ for i in *.dat > do > size=‘wc -c $i‘ > if test $size -eq 0 > then > rm $i > fi > done - The complete for loop can also be edited in a file and, by granting the execute permission on the file , the Shell program can be invoked - By default any shell program is parsed to Bourne shell However, by mentioning #! /bin/sh or #! /bin/csh in the first line of the shell program, it can be parsed to either Bourne shell or C-shell resp’ly
  • 129. Example echo If you have a TTY vt100 enter vt100 echo If you have a TTY AT386-M enter AT386-M echo If you have a TTY sma84 enter sma84 read term case $term in vt1001) TERM=vt100 ;; AT386-M) TERM=AT386-M ;; sma84) TERM=sma84 ;; *) echo ‘Invalid TERM’ ;; esac # Making it is an environment variable export TERM echo end of program This can be a part of your .profile
  • 130. Control Flows IF if (expr) then command; [ else if ] command; [ else ] command; endif SWITCH switch (string) case string1: command; breaksw case string2: command; breaksw default : command; breaksw
  • 131. FOREACH foreach name (word) commands end WHILE while ( expr ) commands end UNTIL until ( expr ) commands end
  • 132. Chapter 5 Advanced Utilities
  • 133. 1. Redirection 2. Pipes 3. Pipe fitting with tee utility 4. Filters 5. Find 6. Sort 7. Utilities that process tabular data- cut, join, csplit 8. Ps and Kill 9. Timely Execution- nohup, at, time 10. User backup utilities- tar, cpio, dd , doscp 11. Output related commands- pr, lpr,lp 12. Other utilities- sleep, sync, wait, clear, tr 13. Introduction to Make 14. Lint 15. Lex 16. YaccAdvanced Utilities
  • 134. Redirection Metacharacter Performs “<“ input “>” output write “>>” output append e.g., $ who trg1 tty00 Apr 8 09:33 trg2 tty02 Apr 8 11:10 $ who > who_out $ cat who_out trg1 tty00 Apr 8 09:33 trg2 tty02 Apr 8 11:10 $ date > date_out $ cat date_out Fri Apr 8 14 : 30 : 10 est 1983 $ who >> date_out $ cat date_out Fri Apr 8 14 : 30 : 10 est 1983 trg1 tty00 Apr 8 09:33 trg2 tty02 Apr 8 11:10
  • 135. Metacharacter Performs “|” piping e.g., Without Pipe $ cat /etc/passwd > temp $ sort < temp $ rm temp With Pipe $ cat /etc/passwd | sort * No need for creation/deletion of a file * Sorts the file passwd as per the first entry in passwd Pipes :
  • 136. A UNIX Pipeline Standard Input >Prgm #1 Prgm #2 Prgm #3 Prgm #4 >Prgm #5 Prgm #6 Standard Output<
  • 137. Helps in creating the intermediate file during the pipe operation e.g., $ ls *.c | tee Cflst | sort $ cat cflst * Creates the intermediate file Cflst * Cflst contains the list of c filesThe TEE Utility :
  • 138. grep get regular expressions only fgrep fast, several simple strings at one time egrep extended grep, can handle more powerful expressions like | - or operatorsFILTERS :
  • 139. $ grep pattern filenames Options : -c number of lines matched -i ignore case -n print line with line-number -v print lines which do not match
  • 140. Searching Files with grep e.g., $ grep -ni func1 *.c Prints all the lines and line numbers in files *.c that match pattern func1 ignoring the case $ grep ‘*’ * Search for the pattern * in all the files $ ls -l | grep ‘^d’ Searches for all subdirectories
  • 141. e.g., $ egrep ‘int|long’ test.c Searches for all those lines containing either int or long in test.c $ egrep ‘ (^[A-Z])’ testfile Searches for all the lines which start with a capital letter $ cat exprfile Searches for lines having at least 3 commas ,.*,.*, in file testfile using the exprfile $ egrep -n -f exprfile testfile
  • 142. Find To locate one or more files find path-list cond-list action-list path-list one or more directory names cond-list -type x x can be d, f, or c d directory f ordinary file c character special file -user name for a specificed user name -group name for a specified group name -size n File size n. blocks If n follows c then so many characters -links n locate for file with n links -atime n files accessed during n days ago -mtime n modified n days ago -ctime n created n days ago -perm nnn permission flags match nnn -name fname with specified filenames
  • 143. actionlist - print display path names - exec command execute the unix command - cpio device copy the files on the tape in specified format - ok command like exec , but executed interactively e.g., find / -atime 7 -print - will print files accessed in exactly 7 days find / -atime +7 -print - will print files accessed earlier than 7 days find / -atime -7 -print - will print files accessed within 7 days
  • 144. Examples $ find / -atime +30 -print $ find / -atime +30 -size +10 -print $ find / -atime +30 -size +10 -ok rm -f {} \; $ find . -perm 0777 -print $ find . -perm 0777 -print -exec rm {} \; $ find / -name passwd -print - Will find the passwd file
  • 145. Sort * Sort keys can be fields or lines * A field is a string of characters separated by a field separator or new line. $ sort {-options} {+post1} {-post2} {files} The sort key begins at post1 ands ends just before post2. There can be several keys. Options b ignore leading blanks and tabs c only check if input file is already sorted d dictionary order letters, digits, blanks f ignore case i ignore non-printable characters n numeric sorting r reverse order tp use p as separator u output only lines with unique keys o filenameout save output in filenameout
  • 146. e.g., $ sort -t: +2n -3 /etc/passwd Print the passwd file sorted by numeric user id $ who | sort +4n Sorts according to the login time stamp of the user
  • 147. uniq Finds and eliminates duplicate lines in a file and is often used with sort $ sort | uniq -c Sorts and ouputs the number of count of lines containing unique fields $ sort | uniq -d Gives only the duplicated lines tsort Accepts as input a partial ordering and produces a fully ordered list of the items. $ tsort psortfile
  • 148. Cut * Deletes columns from a file producing a new file with shorter lines * Cuts out selected fields of each line in a file. * Cuts columns from a table or fields from a file which can be of type - Fixed length fields or - Delimited by some characterProcessing Tabular Data
  • 149. Cut (contd.) cut -c list { file1 file2 ...} e.g., cut -c 5-70 file1 cut would pass 5-70 characters from file1 cut -flist {-d char } {file1 file2....} e.g., who | cut -d” “ -f1 gives a list of user login names cut -d: -f 1,5 /etc/passwd gives a list of user ID and names
  • 150. JOIN * Combines corresponding lines in two files by relating the contents of one or more columns. * Implements a relational data base ‘join’ on two tabular files -jn m join on the mth field of file ‘n’ -on.m output mth field of nth file n - file no. m - field no. -tc use char c’ as separator
  • 151. e.g., $ join -j1 4 -j2 3 -o 1.1 2.1 1.6 -t: etc/passwd etc/group - joins field group id - outputs the following parameters login group login name name dir
  • 152. csplit context split $ csplit [-k] [-f prefix] [-s] file name arg1 [..argn] Reads file and separates it into n+1 section defined by arg1...argn Options : -s Normally csplit prints the character counts for each file , -s is to suppress this -k csplit removes previously created files in case of error , -k is to avoid this csplit normally creates file as xx00 , xx01 ... , xx99 -f prefix creates file with that prefix instead of default xx
  • 153. csplit(contd.) e.g., $ csplit -f cobol inpfile /Procedure division/’ / Para5./ /Para6./ /Para 7./ * Creates file as cobol 00 .. cobol 03 * Edit these Cobol files * Can be recombined as $ cat cobol 0[0-3] > file csplit -k prog.c ‘%main(%’ ‘/^}/+1’ {20} * Breaks file prog.c containing C routine upto a maximum of 21 * ‘% expr %’ —> no. file is created for this section * No csplit for the main routine ‘%main%’
  • 154. PS, kill $ somecommand & 5511 - pid $ps pid tty time command 3432 2 0 : 24 -sh 5765 2 0 : 03 ps 5511 2 0 : 51 somecommand $ kill 5511 $ ps pid tty time command 3432 2 0 : 24 -sh 5985 2 0 : 03 ps
  • 155. $ stubborn-cmd & pid tty time command 3432 2 0 : 24 -sh 6004 2 0 : 03 ps 5995 2 0 : 44 stubborn-cmd $ kill 5995 $ ps pid tty time command 3432 2 0 : 24 -sh 6004 2 0 : 03 ps 5995 2 0 : 44 stubborn-cmd $ kill -9 5995 $ ps pid tty time command 3432 2 0 : 24 -sh 6103 2 0 : 03 ps
  • 156. time Time a command $ time wc test.c > wc.test real 2.0 user 0.4 sys 0.3 nohup Protecting a process from hanging and quit signals or interrupts The standard output is sent to nohup.out e.g., $ nohup du / & 820 Sending output to nohup.out $ logoutTimely Execution :
  • 157. nice * Executes at specified priority * Default priority is 24 $ nice +n Raise priority $ nice -n Lower priority $ nice n set priority at Executes process at specified time $ at 5 pm echo ^G ^G Time to logoff >/dev/tty04 ^D $
  • 158. tar tape archiver Copies files on backup medium such as floppy or tape in tar format tar [options] devicename filelist Options : c create a new tape backup tape old files are overwritten r append files to the tape t list the names of files from backup tape x extract files from the backup medium u update a tape, if the named files are not present or have been modified later on v verbose ; provides informational messages, such as the name of each file as and when it is encountered f devicename use device for backup mediumUser Backup Utilities :
  • 159. tar (example) $ tar cvf /dev/fd096 * copies all files from the current directory onto the backup medium /dev/fd096 $ tar xvf /dev/fd096 Extracts all the files from the backup medium /dev/fd096 onto the current directory Creates necessary directories tar xvf /dev/fd096 try.c Extracts the file try.c from /dev/fd096 tar tvf /dev/fd096 Generates a file list of /dev/fd096 find / -mtime -7 -exec tar uf /dev/fd096 {} \; All the files modified last week is backed up onto /dev/fd096
  • 160. cpio * Copy files archives in and out * Bundles all the files into one package cpio [options] file list devicename Options -o Copy these files onto tap -i Extract files from tape -p Read a list of file or path names from the standard input -v display a verbose set of cpio action -c character information in ASCII for portability considerations -t For listing files from the backup medium -O Append files to the end of tape to be used with -A -d Creates necessary directories -k In case of error , ignore the error and continue
  • 161. cpio (Examples) $ ls *.c | cpio -ocBv > /dev/rmt/0n Lists the files *.c and copy onto the device /dev/rmt/0n $ cpio -ocBv < filelst > /dev/rct/c0s0 Copies all the files mentioned in filelst onto the catridge tape $ cpio -icBdv < /dev/rct/c0s0 Extracts all the files from device c0s0 and creates necessary required directories $ cpio -itv < /dev/rmt/0m List the files from the tape /dev/rmt/0m
  • 162. dd convert, reblock, translate, copy a tape file. dd {option = value } Options Values if input file name of output file name ibs input block size (Default 512) obs output block size(Default 512) cbs conversion block size skip n records before copying from I/P file seek write after n output records in O/P file count n records conv To ASCII, EBCDIC, lcase, ucase (separated by a comma) e.g., $ dd if=/dev/rmt/0n of=x ibs=800 cbs=80 conv=ascii,lcase
  • 163. doscp Copy a UNIX file in DOS format or Copy a DOS file in UNIX format doscp source file target file e.g., $ doscp /usr/trg/test.c a: copies the file test.c onto the floppy $ doscp a:try.c . copies the file try.c from the floppy onto the current working directory
  • 164. pr prepares a file for printing Options -k K col. Output +k from page k -lk set length of page to k lines -p pause after each page -h take next argument as header -wk set width to k characters -d double space e.g., $ pr -3 d h “file list” f1 f2 - Generates a header as file list - 3 Column output - Double spacing $ pr -5 wordlist - Generates 5 column outputOutput Related Commands :
  • 165. pr (contd.) $ pr myfile prepare myfile nov 24 : 11 : 31 1987 myfile page 1 $ pr -t myfile suppresses the header This file can be printed using $ pr myfile | lpr
  • 166. lpr Print a file on the line printer $ lpr myfile prints myfile on the printer $ lpr -c myfile make a copy to the spool directory $ lpr -r myfile myfile is removed from the spool lp Combines the actions of pr and lpr $ lp myfile prints myfile with header, date, time and page numbering.
  • 167. sleep Suspend execution $ sleep 5 prompt appears after 5 seconds $ sync * updates super block * writes all disc buffers * calls sync before stopping system to ensure file system integrity * saves all modifications $ wait waits till all background jobs are over $du determines disk usage -s total blocks -a size of each fileOther Utilities
  • 168. df displays no. of free blocks df [option] file system clear clears the screen and the prompt goes to top of screen tr replaces specified characters with other characters e.g., $ tr “[a-z]” “[A-Z]” < lfile > ufile Replaces all small case letters to upper case letters $ tr -d’ ‘ < tstfl > tstfl2 Deletes all the blank characters $ tr -s ‘\012’ < try > try2 Removes adjacent blank lines in file try
  • 169. Making & Maintaining large programs What is make? Program for maintaining large number of programs Need for make * Difficulties in remembering the dependencies * Simple mechanism for maintaining an up-to-date version of Programs Characteristics * Helps maintain large systems * Specifies dependencies of files in the system and t the actions to make them * Uses creation date to determine the actions to be taken make - An Introduction
  • 170. make : AN INTRODUCTION …Contd... make program takes the file named makefile or Makefile as its input. makefile details: - the names of the files that make up the program system - their interdependencies - how to regenerate the program system Example : final mod1 mod2 mod3
  • 171. make : AN INTRODUCTION …Contd... Example (contd): Makefile or makefile final : mod1.o mod2.o mod3.o cc -o final mod1.o mod2.o mod3.o mod1.o : mod1.c cc -c mod1.c mod2.o : mod1.c cc -c mod2.c mod3.o : mod3.c cc -c mod3.c Run the command as .... $ make final use -f urflname option If the name of the file is not Makefile or makefile
  • 172. Using the Macro facility and Inference rules QSRC = qp1.c qp2.c qp3.c INCLUDES = lim.h com.h OBJECTIF = qp.o qex.o libs.a query : $(OBJECTIF) cc -o query $ (OBJECTIF) qp.o : $ (QSRC) cc -o qp.o $ (QSRC) libs.a : libs(lib1.o) libs(lib2.o) qex.o lib1.o lib2.o : $ (INCLUDES) LIBES = libs(libs1.o) libs(libs2.o) prog : $(OBJECTIF) cc $(OBJECTIF) $(LIBES) -o prog
  • 173. * Reports the various inconsistencies that can exist in a program in the following areas . Syntax errors . Unused variables . Unused arguments . Unused functions . Unused return values . Unused external variables . Unintialized variables . Type checking features . Portability considerations . Statement not reached . Excludes goto statements * Invoked as lint [options] filenameLint - C Program Checker
  • 174. Lint - C Program Checker …Contd... Example : test.c #include main(argc,argv) int argc; char **argv; { int i,j,k,l,number,num2; int int1, int2; int arr[20]; scanf(“ %d”,num2); printf(“The square root of %d is %f \n”, number , sqrt(number) ); i=arr[j++]; add(int1,int2); } add (int1,int2,res) int int1,int2, *res; { printf("The value %d", int 1 + int 2); }
  • 175. Lint - C Program Checker …Contd... Generate an output after invoking lint as lint test.c -lm test.c warning : k , l unused in function main warning : j may be used before set warning : main() returns random to invocation environment Function argument (number) type inconsistency scanf (arg2) int :: format int * : test.c Value type declared inconsistently sqrt llib-lm : test.c Function argument ( number ) used inconsistently sqrt ( arg1 ) : test.c Function called with variable number of arguments add : test.c Function returns value which is always ignored printf scanf
  • 176. source * General tool for separating character strings patterns in an input * String patterns can be specified using rules syntax definitions % % rules % % user subroutinesLex
  • 177. Lex …Contd... Example (on rule) Expression ——> integer * integer Expression ——> integer + integer Expression ——> integer - integer Expression ——> integer / integer The lex specification file %% [0-9]+ { return (INT); } [-*+/] { return (OPR); } [\t ] ; { printf(“Lexical analyser error\n”); exit(-1); }
  • 178. Lex …Contd... %% yywrap() { return(1); } yywrap() indicates no further input available Invoked as $ lex filename $ lex lex.l Generates lex.yy.c
  • 179. What is it? Yet Another Compiler Compiler Features * General tool describing input to a program * Specify input structure * Code for each structure * Outputs a subroutine which handles the input * User supplied routine to supply next basic item Yacc :
  • 180. Yacc …Contd... Specifications Declarations %% rules %% Example %token INT OPR %start expr %% expr : INT OPR INT { printf(“The input expression is correct\n”); } | error { printf (“The input expression is wrong \n”); } %% Invoked as $ yacc filename $ yacc yac.y Generates y.tab.c
  • 181. Consider this program... #include main() { yyparse(); } #include “y.tab.c” #include “lex.yy.c” The whole program can be compiled as ... $ cc main.c -ll -ly -ll and -ly to link lex and yacc library $ a.outA Program using both lex & yacc
  • 182. Chapter 6 Communication Features
  • 183. 1. User communication commands mail write talk post news mesg 2. Networking commands uucp uuto rlogin telnet ftp rcp uux ct cuCommunication Features
  • 184. * Mail * Write * Talk * Post * News * Mesg User Communication Commands :
  • 185. Mail Sends and receives mail messages between users Sending mail on local system At the end of the message press ^D to exit $ mail Example : (Assume the current user is trg) $ mail trg1 Sending mail on remote system $ mail recipient@remote_system.domain_info
  • 186. Receiving mail $ mail Shows the message received ? Prompt q quit s [file] save (defalut mbox) w [file] write without header d delete n or + next message - previous r reply to the sender m [user] mail to user ! cmd run the shell command * The message could be saved or deleted * Environment could be setup in .mailrc
  • 187. User Communication commands …Contd... Write Allows sending messages to a user terminal from another terminal The message is ended by pressing ^D. $ write Talk Allows interactive dialogue between users at two different terminals. $ talk
  • 188. Post Messages can be posted on a “bulletin board” for previewing by all users. News * Keeps the user informed of current events * Refers file /usr/news e.g., $ news Prints all the news , latest first $ news reorg Prints the news named reorg mesg The terminal can be write protected to prevent other users from writing onto your terminal e.g., $ mesg [option] option : - y write allowed - n remove write permission on the terminal $ mesg prints the current status whether mesg is y or n
  • 189. * uucp * uuto * telnet * rlogin * ftp * rcp * uux * ct * cuNetworking Commands
  • 190. uucp * allows copying files from one unix system to another * Refers file uuname and uulog uucp [options] source-files destination files options -d make necessary directory -c do not copy local file to spool directory -m send mail to the requester when the copy is completed $ uucp -d -m file? sys_2!/usr/spool/uucppublic Copies the files file? creating appropriate directories onto system sys_2 onto /usr/spool/uucppublic
  • 191. uuto * Simplified version of uucp * Sends file to /usr/spool/uucppublic $ uuto filename(s) system!login $ uuto -m test.c sys2!trg2 Sends a mail to the sender when the job is over rlogin * Allows remote login over the network * Similar to telnet, but a much more flexible facility. $ rlogin system_name!username
  • 192. Networking Commands …Contd... ftp * File transfer protocol * Transfers files from one system to another $ ftp ftp > open sys1 Name login: passwd ftp > ? Gives you the help ftp > get filename Gets the file onto the current system ftp > put filename Puts the file onto the \ sys1 ftp > close $
  • 193. rcp Similar to ftp, but a much more flexible facility uux * Unix to Unix command execution on remote systems * Gather files from various computers, run a command on a specified computer and redirect the stdout to a file on a specified computer $ uux [options] commandstring All shell special characters must be quoted $ pr minutes | uux -p host!lp Command line queues the file minutes to be printed on the area of the computer host
  • 194. ct * Connect terminal to remote terminal * Connects your terminal to remote terminal which is equipped with a modem This command dials the phone number of the modem $ ct [options] telno $ ct -h -w5 -s1200 9=5553497 ct will call modem using a dialer operating at a speed of 1200 baud , wait for 5 minutes before quitting if dialer is not available and use the -h option not to disconnect the local terminal
  • 195. cu * connects local system to remote system * allows you to be logged on to both simultaneously Examples cu -s2400 9=5557867 Connected login : ~%take proposal Takes proposal from remote computer to local computer ~%put minutes minutes.bak Vice versa of take and puts the file minutes on the remote computer as minutes.bak ~%!comma run the command on local system ~%$command run the command on local and send the output to the remote terminal ~ % . terminate the link
  • 196. Chapter 7 System calls
  • 197. 1. Introduction 2. File related system calls open() read() write() creat() chmod() chown() lseek() 3. Process related system calls fork() getpid(), getppid(), getpgrp() wait() execl() System Calls :
  • 198. * Library functions and system calls * Both are C - functions * Difference lies in their incorporation in the UNIX System * Library functions are referred to as add-ons * System calls are part of the UNIX Kernel * Library functions themselves use system calls and can be expanded by the user * System Calls generally common across UNIX versions * System calls share the concept of fd -file descriptor * File descriptor is an integer used to identify a file
  • 199. Basic tasks in file operations - opening files - reading files - writing in files - creating files - changing the permission of files - changing the owner and group of files - seeking to file-location - closing files
  • 200. open () * open() an existing file int open (filename,mode) char *filename; int mode; filename - character pointer to the name of the file mode - integer signifying the mode 0 for read 1 for write 2 for read and write open() returns the file descriptors on success and returns -1 on error Example : Opening the file “test” in read mode and checking for the error condition fd = open(“/usr/trg/test”,0); if ( fd == -1 ) { printf(“error in opening file test”); exit(1); }
  • 201. read () * File should be opened in read mode * read() an opened file int read (filedesc,buffer,nbytes) int filedesc; char *buffer; int nbytes; filedesc - File descriptor indicating which file to be read buffer - An area of buffer storage for holding the Characters read nbytes - number of characters to be read at a time read() returns the number of characters read and 0 in case ofend of file (EOF) and returns -1 on error
  • 202. Example : Reading the file “test” 100 characters at a time while ( ( n = read(fd,buff,100)) > 0 ) { printf(“file test has contents %s “,buff); }if ( n == 0 ) printf ( “ End of file “); if ( n == -1 ) printf (“Error in reading file test”); When each read is finished the pointer advances by 100 bytes so that the next read picks from there * If the number of characters left are less than nbytes ( in this example - 100 ) then read() will pick up what is left over
  • 203. write () * File should be opened in write mode * write() to an opened file int write (filedesc, buffer, nbytes) int filedesc; char *buffer; int nbytes; filedesc - File descriptor indicating which file to be written buffer - The function takes from buffer and writes them to indicated file nbytes - number of characters to be written at a time write() returns the number of characters written and returns -1 on error
  • 204. Example : while ( ( n = read (fd,buff,100)) > 0 ) { n1 = write (1,buff,100); /* writing to standard output */ /* file id - 1 is for stdout */ if ( n1 == -1 ) printf (“Error in writing on stdout"); } if ( n == -1 ) printf (“Error in reading file test ");
  • 205. creat () * creat() creates a new file or overwrites on the existing file int creat(filename, mode) char *filename; int mode; filename - character pointer to the name of the file mode - Integer signifying the mode The mode is specified in octal code creat returns the file descriptor on success and returns -1 on error
  • 206. creat () …Contd... Example : umask(0000); fd = creat(“newfile”,0666); if ( fd == -1 ) { printf(“error in creating file newfile “); } Creates a file called “newfile” in mode 0666 i.e., read and write permissions for owner, group, and others Note : while creating a new file ensure umask is set to zero Otherwise, If umask had been 0022 in the environment variable, then the effective permission would be mode & ~0022
  • 207. chmod () * chmod() set permissions for the file int chmod (filename, mode) char *filename; int mode; filename - character pointer to the name of the file mode - Integer signifying the mode The mode is specified in octal code chmod() returns 0 on success and returns -1 on error
  • 208. Example : ret = chmod(“test.c”,0600); if ( ret == -1 ) { printf(“error in changing the file permission”); } Changes the permission of file test.c i.e., read and write permissions for owner
  • 209. chown () * System call chown() * chown() set ownership for the file int chown (filename,owner ,group) char *filename; int owner , group ; filename - character pointer to the name of the file owner - owner id group - group id chown() returns 0 on success and returns -1 on error
  • 210. chown () …Contd…. Example : ret = chown(“test.c”,0,1); if ( ret == -1 ) { printf(“error in changing the owner and group of the file”); } Changes the owner and group of the file test.c as root and others respectively
  • 211. lseek () * lseek() changes the position of read-write pointer for the file descriptor int lseek(filedes, offset, origin); int filedes, origin; long offset; lseek() returns new-value of the pointer on success returns -1 on error The value of the pointer depends on origin : 0 set the pointer to offset bytes from the begining of the file 1 increment the current value of the pointer by offset 2 set the pointer to the size of the file plus offset bytes
  • 212. lseek () …Contd... Example : ret = lseek(fd,1000,0); if ( ret == -1 ) { printf(“error in seeking to the 1000’th byte of the file “); } lseek(fd,1000,0) skips the first 1000 bytes of the file and starts reading from the 1001’th byte
  • 213. fork () * fork() creates a new process which is a child process * Child process is a logical copy of the parent process * Parent’s return value is the process id of the child * Child’s return value is 0
  • 214. getpid () getppid () getpgrp () * getpid() returns the process id of the calling process * getppid() returns the parent process id of the calling process * getpgrp() returns the process group of the calling process
  • 215. EXAMPLE fork () , getpid () , getppid (), getpgrp () #include main() { int id ; int pid , pgrp ; int ppid ; id = fork(); printf (“PPID - %d PID- %d id - %d \n”, getppid() , getpid() ,id ); printf (“PGRP - %d \n “, getpgrp() ); }
  • 216. EXAMPLE fork () , getpid () , getppid (), getpgrp () Output PPID - 371 PID - 372 id - 0 - From child Process PGRP - 136 PPID - 136 PID - 371 id - 372 - From Parent Process PGRP - 136 PID - Process-ID PPID - Parent Process - ID ID - Returned value from fork() PGRP - Process-group-ID If PID is equal to the process PGRP then the process is the group leader
  • 217. wait () & execl () * wait() causes a parent to stop running and await the termination of a child process * execl() overlays the original process with a new set of instructions Example on execl() #include main() { int id; printf ( “Parent process \n”); if ( ( id = fork() ) == 0 ) { printf(“Statement from child process\n”); execl(“/bin/date”,”date”,0); } printf(“ Parent process again \n”); }
  • 218. EXAMPLE ON execl() Output Parent Process Statement from child process Parent process again Tue Sep 10 11:34:17 1991 Process forked two processes and parent process avoided execl() to print the final statement i.e parent process did not wait for the child to finish To make the parent wait for the child to finish - wait() can be used The example on execl() gets modified as #include main() { int id; printf ( “Parent process \n”); if ( ( id = fork() ) == 0 ) { printf(“Statement from child process\n”); execl(“/bin/date”,”date”,0); } wait(); printf(“ Parent process again \n”); }
  • 219. OUTPUT OF THE MODIFIED EXAMPLE Parent Process Statement from child process waits for the child to finish Tue Sep 10 11:34:17 1991 Parent Process again
  • 220. Thank you !