Chapter 1 gnu and unix commands
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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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Chapter 1 gnu and unix commands

Chapter 1

GNU and Unix Commands

LPI Linux Certification


Objectives

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


The command line

The Command line

  • System interface is the Shell on Linux it's Bash

  • Shell = Command interpertur.


Shell variable basics

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.


Shell basics

Shell Basics

  • Export

  • To make a variable available to the system use the export command

  • Example : $ export Javapath


Entering commands

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.


Entering multiple commands

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


Command history and editing

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.


History expanders

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.


History editing

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.


Processing text streams using text processing filters

Processing Text Streams Using Text Processing Filters

  • cut,expand,

  • fmt,head,join,

  • nl,od,paste,pr,

  • split,tac,

  • tail,tr,wc,

  • Xargs.


Some commonly used text filters

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.


Sed or stream editor

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.


Preform basic file management

Preform Basic File Management

  • File system Objects

  • Directories and files

  • Inodes

  • Commands


File system objects

File System Objects

  • File system is shaped like a Tree

  • It consist of object that contain other objects


Directories and files

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.


Inodes

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


Management commands

Management Commands

  • CP

  • MKDIR

  • MV

  • RM

  • RMDIR

  • TOUCH


Copy cp

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


Make directory mkdir

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


Move mv

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.


Remove rm

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.


Remove dir rmdir

Remove Dir (rmdir)

  • rmdir [options] directories

  • Delete directories that must be empty

  • -p Remove any intervening parent directories that become empty as a result.


Touch

Touch

  • touch [options] files

  • -a Change only the access time

  • -m change only modification time

  • -t timestamps


Wildcards

Wildcards

  • *

  • ?

  • [characters]

  • [!characters]

  • [a-z]

  • [!a-z]

  • {frag1,frag2,frag3...}


Using unix streams pipes and redirects

Using Unix Streams,Pipes, and Redirects

  • Standard I/O and default file descriptors

  • Pipes

  • Redirection


Standard i o

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.


Pipes

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 .


Redirection

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


Lpi linux certification

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.


Create monitor and kill processes

Create, Monitor and Kill Processes

  • What are processes

  • Process monitoring

  • Signaling Active Processes

  • Terminating Processes

  • Shell Job Control


What are processes

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.


Process monitoring

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


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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.


Signaling active processes

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.


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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 .


Shell job control

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.


Modify process execution priorities

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


Making use of regular expressions

Making use of Regular Expressions

  • Regular Expression

  • Regular expression syntax

  • Using grep

  • Using sed

  • Quoting


What are regular expressions

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.


Regular expression syntax

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.


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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


Grep options

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


Quoting

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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