Unix And Shell Scripting

Unix & Shell Scripting Presenter: Jaibeer Malik August 6, 2004

Agenda Objectives UNIX Shell Scripting Questions Feedback

Session Objectives Understand the basics of Unix Operating Environment Understand the basics of Shell Scripting

Unix History History of the Unix Operating System: - Beginning at AT&T Bell Laboratories - Kenneth Thompson - Dennis Ritchie - Berkeley: The Second School - BSD UNIX - Stallman and Torvalds - GNU and LINUX

Unix Why??? There are only two kind of people who understand 0 1 and who don’t understand 01010101010101010101010101010101010101010101010101010 The features that made UNIX a hit from the start are: Multitasking capability Multi-user capability Portability UNIX programs Library of application software

ARCHITECHTURE The UNIX system is functionally organized at three levels: The kernel, which schedules tasks and manages storage; The shell, which connects and interprets users' commands, calls programs from memory, and executes them; and The tools and applications that offer additional functionality to the operating system

Navigating The File System pwd: Checking your Current Directory cd: Changing Directory mkdir: Making Directories rmdir: Removing Directories ls: Listing Files

General-Purpose Utilities banner: Display a Blown-up Message cal: The Calendar date: Display the System Date who: Login Details tty: Knowing Your Terminal man <command>: Displays help on <command> apropos <keyword>:locates commands by keyword lookup whatis <command>: Brief command description

Handling Files cat: Displaying and Creating Files cp: Copying a File rm: Deleting Files mv: Renaming Files more: Paging Output lp: Printing a File file: Know the file types wc: Line and Word and character counting split: Splitting a File into Multiple Files cmp: Comparing two files

File Attributes ls –l: listing File Attributes ls –d: Listing Directory Attributes stat: Display File Permissions chmod: Changing File Permissions chown: Changing Ownership chgrp: Changing Group chsh: Changing Shell ln: Links umask: Define Defaults File Permissions for a User

The Environment env: Displays Environment Properties .profile: The Script Executed During Login Time PWD: Know your Current Directory HISTSIZE: Define History Size LOGNAME: Login Name SHELL: Your Default Shell HOME: Define Home Directory PATH: Declare Path MAIL: Declare Mail Directory Path alias: Define short-hand names for commands

The Process ps: Process Status <command> &: To run a process in Background bg: To run a process in Background fg: To run a process in Foreground kill: Premature Termination of a Process nice: job execution with low Priority at and batch: Execute Later cron: Running jobs Periodically

Communication And Electronic Mail write: Two-way Communication mesg: Your Willingness to Talk talk: Splits the screen into two windows for chatting mail: The mailer news: To read news messages elm: A screen-oriented mail handler pine: Another mail program finger: Details of Users

Networking telnet: Remote Login ftp: File Transfer (protocol) rlogin: Remote Login Without Password rcp: Remote File Copying

System Administration useradd: Adding Users /etc/passwd: User Information /etc/shadow: Encrypted Passwords userdel: Removing Users fsck: File System Checking df: Checking disk size du: Checking file size groupadd: Adding Group groupdel: Deleting Group groupmod: Modifying Group

The Shell The following table shows the default system prompt and superuser prompt for the C shell, Bourne shell, and Korn shell.

Shell Scripting A universal convention is that the extension .sh be used for shell scripts (or shell programs or shell procedures ). The scripts can be executed in two ways: $ chmod +x <filename.sh> $ sh <filename.sh> read: For taking input from the user Example: $ cat example1.sh #First Simple Example to print the standard input from the user to the standard output. echo “Enter Your Name: “ read name echo “Your name is: $name”

Shell Scripting (Contd..) When arguments are specified with a shell procedure, they are assigned to certain special “variables” or rather positional parameters. $1,$2,etc. The positional Parameters $* Complete set of positional parameters as a single string $# Number of arguments specified in command line $0 Name of executed command $? Exit status of the last command $! PID of last command

Shell Scripting (Contd..) Example: $ cat example2.sh #Example to print the standard input from the user to the standard output using positional parameters. echo “Program: $0 The Number of Arguments Specified is $# The Arguments are $*” echo “Your Name: $1\nYour Extension Number: $2” Example: $ example2.sh Jai 5630 Program: example2.sh The Number of Arguments Specified is 2 The Arguments are Jai 5630 Your Name: Jai Your Extension Number: 5630

Shell Programming (Contd..) The && operator delimits two commands; the second command is executed only when the first succeeds. The || operator delimits two commands; the second command is executed only when the first fails. The exit statement is used to prematurely terminate a program. The if Conditional if condition is true then execute commands else execute commands fi

Shell Scripting (Contd..) Relational Operators -eq Equal to -neq Not equal to -gt greater than -ge greater than or equal to -lt less than -le less than or equal to test uses certain operators to evaluate the condition on its right, and returns either a true or false test $x –eq $y or [$x –eq $y] String tests used by test -n stg true if string stg is not a null string -z stg true is string stg is a null string s1 = s2 true if string s1=s2 s1! = s2 true if string s1 is not equal to s2 stg true if string stg is assigned and not null

Shell Scripting (Contd..) File-related tests with test -e file true if file exists -f file true if file exists and is a regular file -r file true if file exists and is a redable -w file true if file exists and is a writable -x file true if file exists and is a executable -d file true if file exists and is a directory -s file true if file exists and has a size greater than zero

Shell Scripting (Contd..) The case conditional case expression in pattern1) execute commands;; pattern2) execute commands;; pattern3) execute commands;; …… esac The while loop while condition is true do execute commands done

Shell Scripting (Contd..) The for loop for variable in list do execute commands done Example: $ for x in 1 2 4 5 #list has 4 strings do echo “\nThe value of x is $x” done The value of x is 1 The value of x is 2 The value of x is 4 The value of x is 5

Shell Scripting (Contd..) The here document symbol (<<) is used sometimes when we need to place the data inside the script. The here document symbol (<<) is followed by the data and a delimiter. shift transfers the contents of a positional parameter to its immediate lower numbered one. When set –x is used inside a script, it echoes each statement on the terminal, preceded by a + as it is executed.

Example bash-2.03$ cat example3.sh IFS="|" while echo "Enter Department Code: " do read dcode set -- `grep $dcode data` case $# in 3) echo "Department name : $2 Emp-id of head of dept : $3" shift 3 ;; *) echo "Invalid Code" ; continue esac done bash-2.03$ cat data 01|accounts|6213 02|admin|5423 03|marketing|6521 04|personnel|2365 05|production|9876 06|sales|1006

Example (Contd…) bash-2.03$ bash example4.sh Enter Department Code: 99 Invalid Code Enter Department Code: 01 Department name : accounts Emp-id of head of dept : 6213 Enter Department Code: 06 Department name : sales Emp-id of head of dept : 1006 Enter Department Code:

Unix And Shell Scripting

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Unix And Shell Scripting