UNIX Training for Beginners

7/30/2019 UNIX Training for Beginners

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UNIX

andSHELL Scripting

By

Sanju Kumar1141983000



Contents

What Is UNIX? History

Basic Terminology

Files and Directories File Permissions

User Commands

Vi Editor Shells Scripting

Linux Development



What Is UNIX?

A computer operating system. It is designedto be used by many people at the same time(multi-user).

Runs on a variety of processors

Lends itself well to use in scientific research



History

UNIX was invented in 1969 by AT&T BellLaboratories

Ken Thompson and Dennis Ritchie are

credited as the original architects Written in the C language in 1973



Different Flavors, All UNIX

Solaris (Sun) HP-UX (HP)

Linux (open source).. RH, Mandrake etc

Irix (SGI)

Berkeley (Mac OS X based on this)



The Shell

When you log in to interact with UNIX, yousee a “shell prompt” ($,# or %)

The shell is a program that runs constantly

and executes the commands you give it

You can choose which shell you prefer



Files and Directories

UNIX uses a hierarchy to store files Files are simply a named collection of bytes

Directories contain other files

Main.c

USSD/

TTB/

Config.txt Func.c



System Directories

/root- The source of everything

/bin - binaries (executables) for all the commands

/sbin- generally of interest only to super user

/dev - devices, such as printers. Not strictly part of

UNIX. Memory is also a device.

/etc - utilities for managing user’s environment



System Directories cont….

/tmp - temporary storage space; same as C:\TEMP /home – Home Directory for users

/usr/local - user utilities and local libraries

/var – system logs and other stuff

/proc – has runtime system info

(try: cat /proc/cpuinfo)



Some Basic Terms

• Home directory - top of your file tree

• Root directory – root of file system

• Current directory - directory you’re in now

• Dot (.) - slang for the current directory

• Dot-dot (..) - parent of the current directory

• Path - Where to find file or directory– Absolute: /home/sanju/training.txt

– Relative: ~/training.txt

• Wildcard - * (asterisk) can be used to stand forany character



venus:/home/sanju$ ls -la

commandflags

• Commands are the way to “do things” in unix

(no point and click)

• A command consists of a program name and optionscalled “flags”

prompt

What is command?



Handling Files and Directories

mkdir - creates a directory rmdir - removes a directory (must be empty first)

rm – removes file

rm -fr - removes directory and everything below

touch <filename> - creates an empty file

cat <filename> - displays a file on screen

more <filename> - to see a screenful at a time

mv – Move/Renames a file



User Administration

Group(QAT)

Chandni

Sanju

Mukesh



Create Groups and Users

JURXSDGG ದ $GGDJURXS JURXSGHO 'HOHWHDJURXS

XVHUDGG &UHDWHDQHZXVHUDFFRXQW

XVHUGHO 'HOHWHDXVHUDFFRXQW



• GroupsIn Unix, all users belong to at least one group. The idea is that

each person in one group has a similar amount of access to the

system.

• PermissionsPermissions tell the OS who can do what with your files and

directories. Permissions can be set for three categories, theuser, the group and the rest of the world. The permissions are:

read, write, execute

Groups and Permissions



Groups and Permissions cont…

You “own” your files and directories user-group-other read/write permissions -rw-r--r-- 1 sanju qat 164870 27 Feb 17:58 6.bmp

-rw-r--r-- 1 sanju qat 164870 27 Feb 17:57 5.bmp

-rw-r--r-- 1 sanju qat 164870 27 Feb 17:57 4.5.bmp

-rw-r--r-- 1 sanju qat 164870 27 Feb 17:57 4.bmp

chmod command changes permissions

chmod g-rw 6.bmp-rw----r-- 1 sanju qat 164870 27 Feb 17:58 6.bmp



Groups and Permissions cont…

What they do:

files:read – Allows you to read the file

write – Alows you to modify the fileexecute –Allows you run the file as a script or binary program

directories:

read – lets you get a directory listing of fileswrite – lets you add or remove files from directory

execute – lets you access files in the directory



Groups and Permissions cont…Special Commands

Wants to change the user owner?

$ chown <NewOwner> <FileName>

Wants to change the group owner?

$ Chgrp <Newgroup> <FileName>



User Commands

What’s in my directory?• lsconfig.txt ERICSSONHLRSTUB hlrstub.h Makefile newtelserver.c

• ls -lt-rw-rw-rw- 1 sanju sanju 560 May 10 14:35 config.txt

-rwxrwxr-x 1 sanju sanju 21530 May 16 17:26 ERICSSONHLRSTUB

-rw-rw-rw- 1 sanju sanju 1388 May 10 14:34 hlrstub.h-rw-rw-rw- 1 sanju sanju 177 May 16 17:26 Makefile

-rw-rw-rw- 1 sanju sanju 18614 May 16 17:27 newtelserver.c

Man[ual] page: man ls



User Commands, cont.

Where am I?pwd - print working directory

Who am I?

whoami

Who is on the system? What’s running?

who

w



User Commands, cont.

What time is it?date

Fri Sep 29 09:55:11 IST 2006

• Where is a command?which ls

whereis ls

• How do I use a command?man ls

• The “why” is left to you.



More Useful Commands

cd - change directories (built into shell) wc - word, line, character, and byte count

echo - echo characters back (print)

passwd - change password

sort - sort lines of a text file



More Useful Commands, cont.

cp - copy a file(s) ps - status of processes (what’s running)

history - list of previous commands

alias - create a shorthand for a command

kill – kill a process



More Useful Commands, cont.

• ln – creating links (kind of like shortcuts, butthey work right), HARD and SOFT

• finger – get some information on other users

• diff – find the difference between two (text)

files



Exercise

Let’s copy a file to our directory.



Tar and Compress

Tar stands for “tape archive” but is more often used to gathera files into one bundle

Get in directory above the one you want to bundle

tar -cvf dir_name > diry.tar

To “untar”, usetar -xvf diry.tar

To compress a tar file, use

compress diry.tar or gzip diry.tarTo uncompress, use

uncompress diry.tar.Z or gunzip diry.tar.gz



– used for shell-attempted filename matching

– special characters for wildcards:

*, ?, []

* : matches any string of zero or more characters(special case: a lone * will not match files starting with '.')

? : matches exactly one character

[] : matches any single character within the square

brackets

Wildcards



Finding and Searching

find - a tricky but useful commandfind . -name myfile -print

find . -name ‘*name*’ -print

• grep - stands for “general regular expression print”Search all files for a pattern:

grep -i FUNCTION_FIND *.c

sanju.c: FUNCTION_FIND(*abc, *tg)

Count the number of occurrences of gee whiz in all thefiles:

grep -c FUNCTION_FIND *.[ch]



Input/Output (I/O) andRedirection

Input can be given from the command line, orfrom a file

a.out < inputfile

Output goes to your screen, or you can “redirect”it to a file

echo “hi there” > out.file

• To append, use >>

echo “hi back at you” >> out.file



Pipes

You can string commands together into asingle command using pipes

who | wc – count : how many users on the

systemps | grep sanju - what am I running now

• Save the results in a file:

who | wc > usercount



Pipes and Redirection>& : redirect all output (both stdout and stderr) to a

file

e.g. ls -l sanju>& sanju.alle.g. my.script >& script.output

|& : include stderr in the pipe

e.g. my. script |& error

Advance commands(pipe and redirection)



File Transfer Protocol (FTP)

FTP is can be used via a command lineprogram (“ftp”) or by any number of graphicalFTP tools.

Interaction is similar to command shells (“cd”, “ls”, etc.) with extra commands to transfer files (“get”, “mget”).

Make sure that you are using binary modewhen transferring non-text files.



Editors

vi & Emacs

Advantage of vi is that it is found on every

UNIX system, while other editors may or

may not be available.



vi – How to use it

vi is not user-friendly!

You have to remember all of the

commands, in addition to which modethe editor is in.

However, vi is very powerful and fastonce you have mastered it.



vi – How to use it

Start vi with a command such as:

$ vi filename

There are three modes:command, insert , and colon mode.

The editor starts in command mode.



vi – What it looks like

Hello, this is the file “sanju" and we are

editing it with vi.~

~

~~

~

~

~

~

“sanju" 1L, 61C 1,1

All

File contents

Line and character count

Current editing

position

Empty line



vi – Modes

Command mode – initial state, <ESC>

cancels partial command

Insert mode – entered with ‘a’, ‘i’, etc., exit with <ESC>

Colon mode – entered with ‘:’,



vi – Command mode

dw delete word

dd delete line4dd delete 4 lines

x cut character

^F move forward one page

^B move back one page$ go to end of line

% find matching bracket

i insert

a appendr replace

u undo

. repeat command

: enter last line file mode



vi – Last line mode

: – enter last line file mode

w – save

q – quit

wq – save and quit

q! – force quit, discard changes

e <filename> – open new file

e! – re-edit current file

! <cmd> – execute shell command



vi Demo

Let’s find out what we can do…



Shell Scripting

To automate frequently used commands

As interfaces between off-the-shelf and companydeveloped software

As applications performing tasks all their own, orautomating basic system administration tasks

Scripts are useful for smaller jobs. They areinterpreted by the shell rather than compiled, sothey run fairly slowly



The Shell Script File

The script file will and should contain more information than just the commands needed to produce the desired output.

Comments--non-executablestatements included in a source codefile to explain the source code

A comment is signified by the # (hash/pound) sign.



SCRIPT HEADER

#!/bin/bash#Filename: FindReplace.sh

#Author: Sanju Kumar

#Group: QA & Testiing

#Created: 28-Sep-2006

##Description: This script takes an input as a string and replace its withanother string provided from command prompt.

Note: You will not receive full credit on lab assignments going forward unless your shell scripts contain a header like the example above.

The .sh file extension is not necessary, but is a convention that is widely used. We will use it in our class.

The Shell Script File



Using the Shell as a Programming Language

Shell Variables--symbolic names thatcan access values stored in memory foruse by the script program

Operators--symbols that representmathmatical or logical operations

Logical Structures--structures that

define program logic (loops, if statements, etc.)



C Shell versus Bourne ShellSyntax

C Shell is an older syntax, still commonlyused

More modern C Shell-like shells include

tcsh Bourne Shell added some desirable features

but has different syntax for some things

Newest Bourne Shell variants are KornShell (ksh) and Born Again Shell (bash)



Command arguments

$./MyScript.sh <FirstArgu> <SecondArug>

A shell script to swap files:

#! /bin/bash

cp $1 tmp

cp $2 $1

cp tmp $1



Variables

There are a number of predefined shell variables, suchas $HOME, $PATH

User can also set “environment variables”:

C shell: setenv SANJU TESTING

Bourne: SANJU= TESTINGexport SANJU or export SANJU = TESTING

Korn: export SANJU = TESTING

• To set a variable in C shell, use set x=1• To set a variable in Bourne, just use x=1



if-then-else

if ( expr ) simple-command

if ( expr ) then

commandlist-1

[else

commandlist-2]

fi



if-then-else cont’d

An example:

if [ $? –eq 2 ] then

echo “we need two parameters!“

elseecho “Two arguments provided!“

endif



Loops

while ( expr )

commandlist

end

For var <worddlist>

commandlist

end



More Shell Commands: basicflow control

– commands:if, else, endif, while, end, for

if ( $user == "sanju" ) then

echo 'the user is SANJU!‘

endif

value = 5

fact = 1

while ( $value > 0 ) #infinite loopEcho “ I am printing this again and again”

End



More Shell Commands: basicflow control

for i in 1 2 3 4 5

doecho $i

done



More Shell Loops

LOGS=mylogfile

TODAY=`date +%m-%d-%y`

for i in `cat $LOGS`

do

mv $i $i.$TODAY

chmod 664 $i.$TODAY

done



Hmmmm.

Okay, shell scripts are useful, but a

little boring.



Awk and Sed

translate input file: “stream editor” (sed)

sed 1,10d filename.txt> New.txt→ delete 1 to 10th linefrom file.

more complex processing of “records”→ awk

ps -ef | awk '{ print $2}‘

Show only second column of “ps –ef”

awk assumes input separated by spaces (can

change)



Homework

Write a shell script that reads a file and replaces a

particular text string with another, all input giveninteractively.

Hint: Use sed for text replacement.

PROCESS



• When you run a command, it starts a new “process”

• Each process has a unique number called the PID(Proccess ID)

• Unix is a multitasking operating system, so you canrun multiple processes simultaneously

• After you start a process, it is usually in what is

called the “foreground.” That is, it takes over yourshell.

PROCESS

PROCESS



• You can suspend processes in the foreground withCtrl-Z

• The process is now frozen. You can pull it to theforeground again by typing “fg”.

• Alternately, you can make it keep running, but put itin the background so can still use the same shell bytyping “bg”.

• You can also start a task in the background by puttinga & at the end of the command.

PROCESS cont…

PROCESS



• You can list all the processes that have been run fromthe current shell with “ps”

• If you want to end a process, you can do “kill <pid>”eg. kill 3724

• If that doesn’t kill it, you can do the “super kill,”

“kill -9 <pid>” eg. kill –9 3724

PROCESS cont…

PROCESS



• You can list all the processes that have been run from the currentshell with “ps”

• To list all the processes on the system, do “ps -ef”

1175 8152 8151 0 17:48 pts/4 00:00:00 -bash

sanju 8204 4145 0 17:50 pts/1 00:00:00 ksh

root 8316 1 0 18:01 ? 00:00:00 httpd

PROCESS cont…

• If you want to end a process, you can do “kill <pid>”

eg. kill 8152

• If that doesn’t kill it, you can do the “super kill,” “kill -9 <pid>”eg. kill –9 8152



Linux Development

What the tools are

What the tools do

Makefile concepts and how-to

Debugging concepts and guidelines

Examples: g++ and gdb



Available Tools

Compilers– C/C++ : cc , gcc , g++

– Java : javac , jikes

– Fortran: f77 , g77

Debuggers

– Text : gdb



Available Tools

Project/Build Management– Versioning Systems : cvs

– Conditional Rebuild: make



Example: A Basic Compile

g++ syntax:

g++ [<options>] <input files>

Some useful options:

-g produce debugging info (for gdb)

-Wall “W arnings all”

-ansi force ANSI compliant compilation

-o <name> output filename

Example:

g++ -g -o hello hello.cpp



The Make Command

make syntax:

make [-f <file>] [<target>]

argument descriptions:

-f <file> use <file> as the makefile

default: Makefile or makefile

<target> compile configuration “target”

default: first target in the makefile



Makefile Syntax

Rule Syntax:

<target>: <requirements>

<command>

The <requirements> may be files and/or other targets

It must be a tab before <command>, or it won’t work

The first rule is the default <target> for make

Variable Syntax:

<variable>=<string value>

All variable values default to the shell variable values



Example Makefile# Example Makefile

CC=gcc

CCOPTS=-g

Application: foo.o bar.o

$(CC) $(CCOPTS) –o Application foo.o

bar.o

foo.o: foo.cpp foo.h

$(CC) $(CCOPTS) –c foo.cpp

bar.o: bar.cpp bar.h

$(CC) $(CCOPTS) –c bar.cpp



Make Power Features

“Fake” targets

– targets that are not actually files

– can do just about anything, not just compile

– like the “clean” target

clean:

rm foo.o bar.o foobar



Anything Else?



Thanx

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