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LPI Linux Certification

Chapter 1 GNU and Unix Commands. LPI Linux Certification. Objectives. Understanding and use of the Command Line Use of Text Streams and Processing Filters Basic File Management Using Streams , Pipes and redirects Create, change and kill processes Change the Priority of a process

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LPI Linux Certification

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  1. Chapter 1 GNU and Unix Commands LPI Linux Certification

  2. Objectives • Understanding and use of the Command Line • Use of Text Streams and Processing Filters • Basic File Management • Using Streams , Pipes and redirects • Create, change and kill processes • Change the Priority of a process • Using regular expressions

  3. The Command line • System interface is the Shell on Linux it's Bash • Shell = Command interpertur.

  4. Shell Variable Basics • PS1 contains the system prompt • Uses echo to display value of any shell variable • Example : echo $PS1 • PATH • The path variable contains information used by the shell to find and launch programs or commands.

  5. Shell Basics • Export • To make a variable available to the system use the export command • Example : $ export Javapath

  6. Entering commands • Commands consist of 4 general components • A valid command(shell or program or script) found along the PATH of directories listed in the PATH variable • Command options • Argument , such as file names • Line acceptance , the enter key.

  7. Entering multiple commands • Commands can be entered interactively by using the programming feature of the shell • Multiple command can also be entered on the same line separated by a semicolon. • Example : $ls;ps

  8. Command History and Editing • You can use command history to recall recent typed commands. • The size of the history is controlled by the HISTFILE shell variable. Set by default to 500 lines . You can adjust this by adjusting HISTFILE. • Use the history command to view the history file.

  9. History expanders • !! most recent command • !n refers to command “n” from the history • ! -n current command minus n from history • ! string most recent command starting with string • !? String most recent command containing string • ^ string1^string2 Substitution of string one for string two.

  10. History editing • Control- P or Up Arrow , gives previous . • Control-n or Down Arrow , next . • Control-b or Left , one char left. • Control-f or Right , one char right. • Control-a , beginning of line . • Control-e , end of line • Additional command on page 18 of text.

  11. Processing Text Streams Using Text Processing Filters • cut,expand, • fmt,head,join, • nl,od,paste,pr, • split,tac, • tail,tr,wc, • Xargs.

  12. Some commonly used Text-Filters • head : prints the first few lines of a file or files • Syntax: head [options] [files] • Tail : prints the last few lines of a file. • Example : tail -f /var/log/messages • This would allow you to see entries into the log files as the were occurring. The -f switch means follow.

  13. Sed or Stream editor • Is intended as a text filter • Can be called from the command line or from a file • Uses regular expressions • Useful in doing substitution or removals of know text from a file or groups of files.

  14. Preform Basic File Management • File system Objects • Directories and files • Inodes • Commands

  15. File System Objects • File system is shaped like a Tree • It consist of object that contain other objects

  16. Directories and Files • Directories are objects intended to contain other objects • Files are objects intended to contain information • The top of the directory is called the root it is represented by the “/” • All other objects can be referenced by there relationship to “root” in tree like manner.

  17. Inodes • Inodes are the objects that hold the identification information about object in the tree. Such as location on the disk , modification time and security settings. • Each ext2 file system is created with a finite number of inodes

  18. Management Commands • CP • MKDIR • MV • RM • RMDIR • TOUCH

  19. Copy (cp) • cp [options] file1 file2 • -f force overwrite • -i prompt interactively before proceeding • -p Preserve all file attributes such as ownership and permissions as well as time stamp • -r -R recursively copy directories • -v Display the name before copying

  20. Make Directory (mkdir) • mkdir [options] directories • Make one or more directories , you must have write permissions in the directory your trying to create more directories in. • -m set the access mode for directory • -p Create parent directory if needed • ~ , is used as a short cut to user home directory

  21. Move (mv) • Move or rename files and directories • mv [options] source target • -f Force the move even if target exist, suppressing warning messages • -i Query interactively before moving file.

  22. Remove (rm) • Delete one or more files • rm [ options ] files • To remove a file you must have write permission in the directory that holds the file. • -d removes directory that are not empty • -f Force removal with out prompting • -i interactive mode • -r, -R if file is directory recursively remove all contents.

  23. Remove Dir (rmdir) • rmdir [options] directories • Delete directories that must be empty • -p Remove any intervening parent directories that become empty as a result.

  24. Touch • touch [options] files • -a Change only the access time • -m change only modification time • -t timestamps

  25. Wildcards • * • ? • [characters] • [!characters] • [a-z] • [!a-z] • {frag1,frag2,frag3...}

  26. Using Unix Streams,Pipes, and Redirects • Standard I/O and default file descriptors • Pipes • Redirection

  27. Standard I/O • Standard input ( stdin) default is keyboard also known as file descriptor 0. • Standard output (stdout) default is the screen also known as file descriptor 1. • Standard error (stderr) default is also the screen also known as file descriptor 2. • All three streams may be redirected at will.

  28. Pipes • Pipes take output from one program and “Pipe it into another program , thus standard output from a program can become standard input to another • By chaining the output of one command to the input of another command you can produce some very powerful applications .

  29. Redirection • Use redirection to send standard output to another place like a file. • Shell redirecting operators are: > , >> , < and | • See table 1-10 for useful Standard I/O redirection operator syntax

  30. Tee • Read from standard input and write to both standard output and one or more files. • tee [ options] files • -a Append to files rather than overwrite.

  31. Create, Monitor and Kill Processes • What are processes • Process monitoring • Signaling Active Processes • Terminating Processes • Shell Job Control

  32. What are Processes • Every command or program executed on your operating system is a process • Each has these quality's • A lifetime , process ID , user and group ID, parent process ID, environment and current working directory.

  33. Process Monitoring • ps [options] • Generates a one time snapshot of current processes. • The most common form is ps -aux • See manual for all the options , man ps. • pstree [options] [pid|user] • Shows a tree representation of the processes , similar to using ps -f

  34. Top • top [command -line options] • Produces a continually updated display of all processes . • Has an interactive mode allowing you to enter commands such as kill . • Displays most of the same information as ps does.

  35. Signaling Active Processes • All processes listen for signals . • Signals are numeric integer messages • Most common used signals are: HUP,INT,KILL,TERM,TSTP. • Each have a corresponding number 1,2,9,15,and 18 respectively. • To see all the signal on your machine type {kill -l} for a list.

  36. Kill • Kill is used to stop a process or series of processes. • Kill [-s sigspec | -sigspec] [pids] • See examples in the book • Use ps or top to identify the process ID and then use the kill command to kill it . • Kill -15 1001 , this means kill using the sigterm signal 15 the process 1001 .

  37. Shell Job Control • Allows you to place executing programs in the background and bring them into the foreground • The shell command $ netscape & place the netscape program in the background , it returns a job number and a PID number. • Use the bg , fg and jobs commands to control background jobs.

  38. Modify Process Execution Priorities • Be nice use nice and renice • Nice , assigns a priority number for program execution at the time it is executed. Renice is used to change the priority of a running program. • Nice numbers range from -20 to +19 the lower the number the higher it's priority • Only root can lower a nice number • All user processes start at zero (0) • See the book for syntax instruction

  39. Making use of Regular Expressions • Regular Expression • Regular expression syntax • Using grep • Using sed • Quoting

  40. What are Regular expressions • Regular Expressions are strings used in matching operations . The values inside the regular expression is used to search for or match a string. • Regular expressions make extensive use of place holders and wildcards , as well as reserve symbols to represent actions and values.

  41. Regular expression syntax • Methacharacters , Characters that take on special meaning . • ^ the beginning of a line or $ end of a line. See table 1-12 , 1-13,and 1-14 for a expanded list • Literals everything not a Methacharacter. • Position Anchors , such as ^ or $. • Character sets , used to match text • Modifiers , change the meaning of other characters in the expression.

  42. Grep • Syntax : grep [options] regex [files] • Grep evolved from a line editor (ed) command into a utility of it's own. • Used to search files or standard input for lines containing a match of the regular expression

  43. Grep Options • -c Display only a count of the lines that match • -h Display matched lines • -i ignore case • -n display match lines with line numbers • -v print all lines that do not match the regexp

  44. Quoting • To use Regular expression on the command line with grep and sed you must escape those Metacharacters you don't want the shell to expand. • The backslash \ is used \* • Single quotes '*' • Double quotes “*” • All stop the shell from expanding them .

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