1. Review Chapters 5 thru 8

2. 2 Two Groups of Commands Select commands Manipulate and Format commands

3. 3 Using the Select Commands Select commands: grep, diff, uniq, comm, wc Using Pipes – The pipe operator (|) redirects the output of one command to the input of another command An example would be to redirect the output of the ls command to the less command The pipe operator can connect several commands on the same command line

4. 4 Using Pipes Using pipe operators and connecting commands is useful when viewing directory information ls /etc | sort –r | less

5. 5 Using the grep Command Used to search for a specific pattern in a file, such as a word or phrase grep’s options and wildcard support allow for powerful search operations You can increase grep’s usefulness by combining with other commands, such as head or tail

6. 6 Using the grep Command grep can take input from other commands and also be directed to provide input for other commands grep IBM /etc/termcap | head

7. 7 Using the uniq Command Removes duplicate lines from a file It compares only consecutive lines, therefore uniq requires sorted input Uniq has an option that allows you to generate output that contains a copy of each line that has a duplicate

8. 8 Using the comm Command Used to identify duplicate lines in sorted files Unlike uniq, it does not remove duplicates, and it works with two files rather than one It compares lines common to file1 and file2, and produces three column output Column one contains lines found only in file1 Column two contains lines found only in file2 Column three contains lines found in both files

9. 9 Using the diff Command Attempts to determine the minimal changes needed to convert file1 to file2 The output displays the line(s) that differ The associated codes in the output indicate that in order for the files to match, specific lines must be added or deleted

10. 10 Using the wc Command Used to count the number of lines, words, and bytes or characters in text files You may specify all three options in one issuance of the command If you don’t specify any options, you see counts of lines, words, and characters (in that order)

11. 11 Using the wc Command The options for the wc command: –l for lines –w for words –c for characters wc –l /etc/passwd

12. 12 Using the Manipulate and Format Commands These commands are: sed, tr, pr Used to edit and transform the appearance of data before it is displayed or printed

13. 13 Translating Characters Using the tr command tr copies data from the standard input to the standard output, substituting or deleting characters specified by options and patterns The patterns are strings and the strings are sets of characters A popular use of tr is converting lowercase characters to uppercase

14. 14 Using the pr Command to Format Your Output pr prints specified files on the standard output in paginated form By default, pr formats the specified files into single-column pages of 66 lines Each page has a five-line header, its latest modification date, current page, and five-line trailer consisting of blank lines

15. 15 Running a Shell Script You can run a shell script in virtually any shell that you have on your system The Bash shell accepts more variations in command structures that other shells Run the script by typing sh followed by the name of the script, or make the script executable and type./ prior to the script name

16. 16 Using UNIX/Linux Shell Scripts After creating shell script, the OS is instructed that the file is an executable shell script via the chmod command Script files can be run in several ways: Set the path variable and type the script name at the command prompt Type./filename if script is in current directory Type the script name preceded by the full path

17. 17 Using Comments Comments are important! Provide useful documentation to both the programmer and to others who need to understand or debug the code To use, start comment line with a #

18. 18 Variables Variables are symbolic names that represent values stored in memory Three types of variables: Configuration variables store information about the setup of the OS Environment variables hold information about your login session Shell variables are created at the command prompt or in shell scripts and are used to temporarily store information

19. 19 Variables Use the printenv variable to see a list of environment variables. You can also use env Look at the man pages. What is different between the two commands?

20. 20 Environment and Configuration Variables

21. 21 Environment and Configuration Variables

22. 22 Environment and Configuration Variables

23. 23 Environment and Configuration Variables

24. 24 Shell Variables Shell Variables are variables that you can define and manipulate for use with program commands in a shell Observe basic guidelines for handling and naming shell variables I recommend that you use all UPPERCASE characters when naming your variables

25. 25 Shell Variables Variables are handled differently depending on the syntax Type: echo $USERNAME echo “$USERNAME” echo ’$USERNAME’ echo `$USERNAME`

26. 26 Shell Operators Bash shell operators are in four groups: Defining operators Evaluating operators Arithmetic operators Redirection operators

27. 27 Defining Operators Used to assign a value to a variable Most common is = (equal sign) Use quotation marks with strings Backquote says execute the command inside the backquotes and store the result in the variable

28. 28 Evaluating Operators Used for determining the contents of a variable echo $variablename will show the value of variablename Double quotes can be used, but not single quotes

29. 29 Arithmetic Operators

30. 30 Arithmetic Operators (continued) Regular mathematical precedence rules apply to arithmetic operators To store arithmetic values in a variable, use let statement let x=6+4*2 echo $x

31. 31 Redirection Operators The > redirection operator overwrites an existing file -o noclobber option of set command will prevent overwriting

32. 32 Exporting Shell Variables to the Environment Shell scripts cannot automatically access variables created and assigned On the command line By other scripts Make variables global in your environment by using the export command

33. 33 Modifying the PATH Variable PATH variable controls where your shell will look for shell scripts You can add directories to your PATH Special directories for scripts Your current working directory

34. 34 Shell Logic Structures Four basic logic structures needed for program development are: Sequential logic Decision logic Looping logic Case logic

35. 35 Sequential Logic Commands are executed in the order in which they appear in the script or program The only break in this sequence comes when a branch instruction changes the flow of execution by redirecting to another location in the script or program Used for simple, straightforward command sequences

36. 36 Decision Logic Enables your script or program to execute a statement or series of statements only if a certain condition exists In many cases, the condition depends upon the result of a command or on a comparison The if statement is the primary decision- making control structure in this type of logic

37. 37 Looping Logic A control structure repeats until some condition exists or some action occurs Two common looping mechanisms: for loops cycle through a range of values until the last in a set of values is reached The while loop cycles as long as a particular condition exists

38. 38 Program control structures can be entered from the command line Wildcard characters can be used in loops The while loop is set up to test repeatedly for a matching condition The while loop is used when code must be repeatedly executed an undetermined number of times Looping Logic (continued)

39. 39 Case Logic The case logic structure simplifies the selection from a list of choices It allows the script to perform one of many actions, depending on the value of a variable Two semicolons (;;) terminate the actions taken after the case matches what is being tested

40. 40 Using Shell Scripting to Create a Menu Often useful to create a menu that branches to specific shell scripts The tput command is useful when creating menus Can initialize the terminal display to place text and prompts in specific locations and respond to the user

41. 41 Debugging a Shell Script A shell script will not execute if there is an error in one or more commands Running a shell script using sh enables quick debugging of problems sh -v option displays lines of code in the script as they are read by the interpreter sh -x option displays the command and its arguments line by line as they are run

42. 42 Customizing Your Personal Environment When programming and shell scripting, customizing your environment by modifying the initial settings in the login scripts provides many benefits Login scripts run just after logging in Setting up personal bin directories and modify editor defaults are common customizations

43. 43 Customizing Your Personal Environment An alias is a name that represents another command The.bashrc file in your home directory is used to establish customizations that take effect at each login The.bashrc script is executed each time a shell is generated, such as when shell scripts are run

44. 44 The trap Command The trap command causes a shell program to automatically remove temporary files created when shell scripts run Programmers often set up a subdirectory to store temporary files, and when a script file exits, trap removes the files Having files removed from a temporary directory like this is considered “good housekeeping”

45. 45 Putting It All Together in an Application Applications require you to: Assign and manage variables Use shell operators Employ shell logic structures Use additional wildcard characters Use tput for managing screen initialization Use trap to clean up temporary files Will use these skills to build a shell script application in Hands-on Project

46. 46 Understanding UNIX/Linux Utilities UNIX/Linux utilities let you Create and manage files Run programs Produce reports Monitor and maintain the system Recover from a range of errors New utilities are continually being added in order to make UNIX/Linux run more efficiently

47. 47 Understanding UNIX/Linux Utilities Classified into eight major areas: File processing System status Networking Communications Security Programming Source code management Miscellaneous

48. 48 File Processing Utilities catDisplay filesfmtFormats text cpCopy filesgrepMatches patterns in files cpioCopy/back filesfgrepMatches patterns in files cutSelects char/fieldsgzipZip/compress files ddConvert/copy a file/imagegunzipUnzip/uncompress files dumpBacks up filesheadDisplays 1 st part of files fileDisplays file typeispellSpell Checks findFinds fileslessDisplays files

49. 49 File Processing Utilities lnCreates symbolic linkspwdDisplays current directory lprSends file to printerrmDeletes files/directories lsLists files/directoriesrmdirRemoves/directories manDisplays man pagessortsSorts files/input mkdirMakes directoriestailDisplays end of files mkfsBuilds filesystemstarCopies and archives files mountMounts filesystemstouchChanges files dates mvRenames/moves files/dir’swhereisLocates info on files

50. 50 Classifying UNIX/Linux Utilities

51. 51 Classifying UNIX/Linux Utilities

52. 52 Classifying UNIX/Linux Utilities

53. 53 Classifying UNIX/Linux Utilities

54. 54 Classifying UNIX/Linux Utilities

55. 55 Classifying UNIX/Linux Utilities

56. 56 Using the dd Command Allows you to copy a file and change the format of the destination file Has a rich set of options to handle copies when other methods are inappropriate An advantage to using the dd command over cp is that all users, not just the administrator, can copy files to and from the floppy drive

57. 57 Checking Hard Disk Usage To maintain adequate hard disk free space, use these strategies: Be vigilant against running dangerously low on free space by using the df command Watch for conspicuous consumption using the du command Follow a routine schedule for “garbage” collection and removal by using the find and rm commands

58. 58 Removing Garbage Files Garbage files are temporary files that lose their usefulness after several days Two examples of garbage files are core files (named core) and a.out files Use the find command to assist you in locating these files and the rm command to remove them

59. 59 Using System Status Utilities System status commands reflect the system’s performance System engineers primarily use the data related to system status Good to know how to obtain and store relevant information to send to system administrator and tune-up specialists

60. 60 Using the top Command One of the most effective utilities for auditing system performance is the top command The top command displays a listing of the most CPU-intensive tasks in real time Updates every five seconds by default

61. 61 Using the uptime Command uptime tells you how long a system has been running since the last time it was booted Displays current time how long the system has been up number of users on the system the load average for 1, 5, and 15 minutes

62. 62 Using the free Command The free utility displays the amount of free and used memory in the system

63. 63 Managing Processes A process is identified through a unique number called a process id (pid) Unix/Linux offer utilities to run, monitor, and kill processes using pids

64. 64 Running Processes in the Background Can run a process in the background while working with another program in the foreground To run a program in the background, append the & character to end of the startup command, e.g., top& Another method is the bg and fg commands

65. 65 Monitoring Processes The ps command with the –A or -a option shows a list of all system processes currently running ps -ax

66. 66 Killing Processes Administrator with root privileges can kill any user’s processes User can kill owned processes Use kill command with the pid of the process Use kill –9 to stop a process that doesn’t respond to an initial kill command

67. 67 Checking the Spelling of a Document ispell scans a document, displays errors on the screen and suggests alternative spellings

68. 68 Comparing Files Use the cmp utility to compare the contents of two files, and report the first difference between them The cmp command displays the position and line number of this difference If there are no differences, the cmp command displays nothing

69. 69 Formatting Text in UNIX/Linux Text formatting in UNIX/Linux involves preparing a text file with embedded typesetting commands and then processing the file UNIX’s nroff and troff commands were the early standard in formatting programs groff is newer version of both nroff and troff