Karkha unix shell scritping

Welcome to UNIX and Shell Scripting workshop
BY
R.Chockalingam

Contact Us
https://www.facebook.com/Karkhadotcom
Ph : 9543111174,9789989552.

UNIX

Multitasking , Multiuser
Operating System.
Unix operating systems are
widely used in servers
,workstations and mobile
devices.

The Unix system is composed of several components
In addition to the kernel of an operating system – the
development environment, libraries, documents, and
the portable, modifiable source-code for all of these
components

UNIX as an Operating System
All operating systems provide services for programs
they run
Executing a new program.
Opening a file.
Reading a file.
Allocating a region of memory.
Getting the current time of day etc …

The Kernel and the Utilities

The Unix system is itself logically divided into two
pieces: the kernel and the utilities.
The kernel is the heart of the UNIX system and
resides in the computer's memory from the time the
computer is turned on and booted until the time it is
shut down.
The utilities, on the other hand, reside on the
computer's disk and are only brought into memory as
requested.

Architecture of the UNIX
operating system

Connecting Remotely
 You must connect to a public CS machine.

 Public Machines:

 Linux Machines (all of them are now running a Lucid build):
juiblex, mig, totoro

 In order to find available cshosts
 Type cshosts pub on the command line for public machines or use the online list:
 http://apps.cs.utexas.edu/unixlabstatus/

 To log in, use a SSH program such as SSH Secure Shell or PuTTY (both
available from Bevoware).
 https://www.utexas.edu/its/bevoware/download/
 When connecting, enter a machine name as follows: name.cs.utexas.edu

File Types
Two different types of files in UNIX are
1. Regular files and
2. Directories

Regular file. The most common type of file, which
contains data of some form. There is no distinction to
the UNIX kernel.

Directory file. A file that contains the names of other
files and pointers to information on these files. Any
process that has read permission for a directory file
can read the contents of the directory, but only the
kernel can write directly to a directory file.

Block special file. A type of file providing buffered I/O
access in fixed-size units to devices such as disk
drives.

Character special file. A type of file providing un
buffered I/O access in variable-sized units to devices.
All devices on a system are either block special files or
character special files.

Symbolic link. A type of file that points to another
file.

File type macros in <sys/stat.h>
Macro Type of file
S_ISREG() regular file
S_ISDIR() directory file
S_ISCHR() character special file
S_ISBLK() block special file
S_ISFIFO() pipe or FIFO

File System
 The UNIX file system consists of directories and files. Directories
contain files or other directories. Files can be programs, text
documents, etc.
 You can think of a directory as a folder in Windows or Macs.
 Directories contain files or other folders, just like typical operating
systems

 The file system is organized as an inverted tree.
 the directories are branches, and the files are leaves.
 The topmost directory is /, and is called root
 all other directories and files are underneath root.

 All of a user’s files are in a home directory, /u/user
 user is the login name for that account.
 It is abbreviated ~user, mine is ~rivin

 Use the command pwd if you can’t remember which directory you are
in.

File System Structure
The Unix file system is a hierarchical structure that
allows users to store information by name. At the top
of the hierarchy is the root directory, which always
has the name /

The location of a file in the file system is called its
path. Since the root directory is at the top of the
hierarchy, all paths start from /.

Flags and Arguments
 command [flags] [arguments]

 command: The name of the command.
 ls lists the contents of a directory.

 flags: switches that modify the function of the base command. Flags usually begin with a "-”.
 ls –a shows all the files (including hidden files) in the current directory.
 ls –l shows files, in long-listing format, in the current directory.

 Flags can be combined.
 ls –al shows all the files (including configuration files) in long-listing format, in the current directory.
 Flags are swappable, so ls –la will do the same.

 arguments: usually the name of a file or directory to perform operations on.
 ls dirname shows all the files (in normal-listing format) in the directory dirname.

 Flags and Arguments can be combined.
 ls –al dirname shows all the files (including hidden files) in long-listing format, in the directory
dirname.

Text Editors
 pico:

 A very easy to use text editor (the one that is used inside of alpine by default).

 vi:

 A small, fast, consistent text editor that does not have a windows interface.
 Type man vi for various commands to manipulate files.
 Type :help inside of vi to bring up the help file.

 emacs:

 Feature-rich
 Can run with a text interface from within a terminal shell, or in its own window with
menus, etc. Type emacs to start the program and then Ctrl-h t to run a tutorial.
 Emacs will run in its own window when running Xwindows. Just type emacs and the
window will come up.

Basic UNIX Commands
 ls directory: Lists the contents of the directory. If no directory name is given, it will list the
files in the directory you are in.

 cd directory: Change from current directory to directory. If no name is given, it will go to
your home directory.

 mkdir dir1: Create a directory named dir1. Multiple directory names can be given.

 cp file1 file2: Make a copy of file1 and name it file2. If file2 already exists, it will be
overwritten.

 rm file1: Remove the file named file1. Multiple filenames can be given.

 mv file1 file2: Rename file1 as file2
 mv file1 directory2: Move file1 into directory2.
 For example, mv project1 CS310 would move the file project1 into the directory CS310
 The directory CS310 must be created first.

 .snapshot: Grab the most recent version of a file if you accidentally deleted it.

Creating a file
cat>firstfile

To read a file :

%cat > firstfile

Creating a Directory

Creating directories permits you to organize your
files. The command
mkdir project1

Basic Commands
man [section] <command> Look up a command
pwd Display current directory
ls [-al] List directory contents
cd<directory> Change Directory
rm <filename> Delete file
cp <filename> <ending
filename>
Copy file to new location
mv <filename> <ending
filename>
Move file to new location

cat <filename> Display entire file
more <filename> Display file one page at a time
wc [-l|w|c] <filename> Return file statistics: number
of words, lines, and
ps [ax or ef] List processes running on the system
kill -<signal> < process ID> Send end signal to a
running process

Editor
Vi
emacs

vi is the classic screen-editing program for Unix
vi test.txt

i Changes to insert mode
or a (after the character under the cursor)
:w Return Save the file
:w<filename> Save the file to a new name
:q Return To exit vi
Command
:q! Return Quit without saving
Insert Esc key Changes to command mode
mode
Backspace and Delete keys Backspaces or deletes, but
only for data

| The Pipe
|
(shift-)
takes the output of one command and feeds it to another command.

less is a pager (shows you a text file one page at a time).
cshosts shows you all the hosts in CS (many pages).

cshosts | less
takes the output of cshosts (many pages) and runs less on it.

grep string filename looks for instances of string inside of filename.

cshosts | grep mo
tells you the machine names returned by cshosts that contain instances of “mo”.

More UNIX Commands
X acroread filename.pdf: Read a .pdf file. If no filename is given, it
will open the program with no initial file.
- xpdf can also be used.
X gv filename.ps: If you ever get a .ps (postscript) file, use this to view
it. If no name is given, it will open the program with no initial file.
X gimp filename: View a graphics file (.jpg or .gif).

 chkquota: Check your disk-space usage in megabytes.

 gzip filename: Zip a file to conserve space.
 gunzip filename: Unzip a file that is zipped.
 zip/unzip filename: Winzip compatible

 ps uxw (ps –u user): Check the processes you have running.
 kill 14083: Kill the process with PID# 14083.

Electronic Mail
 Your email address is your_login@cs.utexas.edu.

 Mail Programs:
There are literally hundreds of mail readers freely available for UNIX.
 Staff supports alpine, mutt, and thunderbird.

 Reading mail:
Typing alpine with no username puts you into the Alpine mail program.
 Selecting Message Index will show you the contents of your mailbox.

 Sending mail:
alpine username sends mail to the person with the login username. If it’s a
CS login, you can leave off the domain name. Otherwise, use the entire email
address: (name@domain.com).

 Finding addresses:
phone name will try to find someone with that name in CS.

Printing
 All printers are numbered in the CS department as lw# (for example, lw4).
 A banner page is printed with your file to keep users’ work separated.

 lpr
lpr –Plw4 file1 will send file1 to printer number 4, in the Taylor basement lab.

 lpq
lpq –Plw4 will list job numbers of all the files currently in lw4’s print queue (those waiting to
be printed).

 lprm
lprm –Plw4 900 will remove job number 900 from lw4’s print queue (the job number can be
found with lpq).

 less /lusr/share/etc/printcap gives a list of printers and their locations

 Printing FAQ:
http://www.cs.utexas.edu/facilities/faq
http://www.cs.utexas.edu/facilities/documentation/printing-options

The UNIX System Shell Programming

Steps to Create Shell Programs
Specify shell to execute program
Script must begin with #! (pronounced “shebang”)
to identify shell to be executed
Examples:
#! /bin/sh (defaults to bash)
#! /bin/bash
#! /bin/csh
#! /usr/bin/tcsh
Make the shell program executable
Use the “chmod” command to make the
program/script file executable 30

Example: “hello” Script
#! /bin/csh
echo "Hello $USER"
echo "This machine is `uname -n`"
echo "The calendar for this month is:"
cal
echo "You are running these processes:"

Karkha.com
ps

31

Example script output
% chmod u+x hello
% ./hello
Hello ege!
This machine is turing
The calendar for this month is
February 2008
S M Tu W Th F S
1 2 3 4 5 6 7
8 9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
You are running these processes:
PID TTY TIME CMD
24861 pts/18 0:00 hello.csh
24430 pts/18 0:00 csh

Karkha.
32 com

Shell logic structures needed for program
Basic
Logic Structures
development:

Sequential logic
User input
Decision logic
Looping logic
Case logic

Karkha.
33 com

Input to a C shell script
Reading/prompting for user input
Providing input as command line arguments
Accessing contents of files

Karkha.
34 com

Reading user input with $<
Use a special C shell variable:
$<

Reads a line from terminal (stdin)
up to, but not including the new line

Karkha.
35 com

Example: Accepting User Input
#! /bin/csh
echo "What is your name?"
set name = $<
echo Greetings to you, $name
echo "See you soon"

Karkha.
36 com

Example: greetings User Input
% chmod u+x
Accepting
% ./greetings User entered Laura
Flowers
What is your name?
Laura Flowers
Greetings to you, Laura Flowers
See you soon

Karkha.
37 com

Command line arguments
Use arguments to modify script behavior

command line arguments become
positional parameters to C shell script

positional parameters are numbered
variables: $1, $2, $3 …

Karkha.
38 com

Command line arguments
Meaning
$0 name of the script
$1, $2 first and second parameter
${10} 10th parameter
{ } prevents “$1”
misunderstanding
$* all positional parameters
$#argv the number of arguments

Karkha.
39 com

Example: Command Line
Arguments
#! /bin/csh
# Usage: greetings name1 name2
# Input: name1 and name2
echo $0 to you $1 $2
echo Today is `date` $1 $2
echo Good Bye $1 $2

Karkha.
40 com

Arguments
$0 => greetings
$1 => Mark
$2 => Flowers

% chmod u+x greetings
% ./greetings Mark Flowers
./greetings to you Mark Flowers
Today is Mon Feb 16 14:18:03 CST
2008
Good Bye Mark Flowers

Karkha.
41 com

Decision logic
if Statement: simplest forms

if ( expression ) command

if ( expression ) then
command(s)
endif

Karkha.
42 com

Decision Statement
if-then-else
logic
command(s)
else
command(s)
endif

Karkha.
43 com

Decision Statement
if-then-else
logic
command(s)
else if ( expression ) then
command(s)
else
command(s)
endif

Karkha.
44 com

Basic Operators in Expressions
Meaning
() grouping
! Logical “not”
> >= < <= greater than, less than
== != equal to, not equal to

|| Logical “or”
&& Logical “and”

Karkha.
45 com

Expression examples$2
if ( $1 == “next” ) echo

if ( $#argv != 0 ) then
…
endif

if ( $#argv > 0 && $#argv < 5) then
…
endif
Karkha.
46 com

Arguments
#! /bin/csh
if ( $#argv == 0 ) then
echo -n "Enter time in minutes: "
@ min = $<
else
@ min = $1
endif
@ sec = $min * 60
echo “$min minutes is $sec seconds”
Karkha.
47 com

Example: Reading file contents
#! /bin/csh
# Usage: lookup nameOrNumber
set list = "users.txt"
if ( $#argv == 0 ) then
echo -n "Enter name OR z-id: "
set name = $<
else
set name = $*
endif
grep -i "$name" $list
if ( $status ) echo "$name not found" Karkha.
48 com

File Testing operators)
Syntax: if ( -opr filename

opr Meaning
r Read access
w Write access
x Execute access
e Existence
z Zero length
f Ordinary file
d directory

Karkha.
49 com

Example: File Testing
if ( -e $1 ) then
echo $1 exists
if ( -f $1 ) then
echo $1 is an ordinary file
else
echo $1 is NOT ordinary
file
endif
else
echo $1 does NOT exist
endif
Karkha.
50 com

C Shell looping constructs
predetermined iterations
repeat
foreach

condition-based iterations
while

Karkha.
51 com

Fixed number iterations
Syntax:

repeat number command

executes “command” “number” times

Examples:
repeat 5 ls
repeat 2 echo “go home”

Karkha.
52 com

The foreach Statement
foreach name ( wordlist )
commands
end

wordlist is:
list of words, or
multi-valued variable
each time through,
foreach assigns the next item in wordlist to
the variable $name
Karkha.
53 com

Example: foreach Statement
foreach word ( one two three )
echo $word
end

or

set list = ( one two three )
foreach word ( $list )
echo $word
end
Karkha.
54 com

Loops with foreach
 useful to process result of command,
one at a time

Example:
#! /bin/csh
@ sum = 0
foreach file (`ls`)
set size = `cat $file | wc -c`
echo "Counting: $file ($size)"
@ sum = $sum + $size
end
echo Sum: $sum Karkha.
55 com

The while Statement
while ( expression )
commands
end

use when the number of iterations is not
known in advance
execute ‘commands’ when the expression is
true
terminates when the expression becomes
false
Karkha.
56 com

Example: while
#! /bin/csh
@ var = 5
while ( $var > 0 )
echo $var
@ var = $var – 1
end

Karkha.
57 com

Example: while
#! /bin/csh
echo -n "Enter directory to list: "
set dirname = $<
while ( ! -d $dirname )
echo "$dirname is not directory"
echo -n "Enter directory to list:
"
set dirname = $<
end
ls $dirname
Karkha.
58 com

loop control
break
ends loop, i.e. breaks out of current loop

continue
ends current iteration of loop, continues with
next iteration

Karkha.
59 com

loop control example
#! /bin/csh
while (1)
echo -n "want more? "
set answer = $<
if ($answer == "y") echo
"fine"
if ($answer == "n") break
if ($answer == "c") continue
echo "now we are at the end"
end
Karkha.
60 com

loop control example
#! /bin/csh
while ( 1 )
echo -n "Enter directory to list:
"
set dirname = $<
if ( -d $dirname ) break
echo "$dirname is not directory"
end
ls $dirname

Karkha.
61 com

The when a variable can take different
Use
switch Statement
values
Use switch statement to process different
cases (case statement)

Can replace a long sequence of
if-then-else statements

Karkha.
62 com

The switch Statement
switch ( string ) C shell compares
case pattern1: ‘string’ to each ‘pattern’
until it finds a match
command(s)
breaksw
When a match is
case pattern2:
found, execute the
command(s) command(s)
breaksw
endsw
… until breaksw

Karkha.
63 com

The switch Statement
switch (string)
case pattern1:
command(s)
breaksw
case pattern2:
command(s)
breaksw When a match is not
default: found, execute the
commands following the
command(s) default label
breaksw
endsw Karkha.
64 com

Example: switch
switch ($var)
case one:
echo it is 1
breaksw
case two:
echo it is 2
breaksw
default:
echo it is $var
breaksw
endsw Karkha.
65 com

The switch Statement no default,
if no pattern matches and there is
then nothing gets executed

do not omit the breaksw statement !
If you omit the breaksw statement, all the
commands
under the next case pattern are executed until a
breaksw or endsw statement is encountered

pattern may contain wildcards:
*, ?, []
Karkha.
66 com

Example: switch greeting
#! /bin/csh
# Usage: greeting name
# examines time of day for greeting
set hour=`date`
switch ($hour[4])
case 0*:
case 1[01]*:
set greeting=morning ; breaksw
case 1[2-7]*:
set greeting=afternoon ; breaksw
default:
set greeting=evening
endsw
echo Good $greeting $1
Karkha.
67 com

Example C Shell program
AVAILABLE OPTIONS
*******************
[1] Display today's date
[2] How many people are logged on
[3] How many user accounts exist
[4] Exit
Enter Your Choice [1-4]:

Karkha.
68 com

userutil shell script 1 of 2
#! /bin/csh
# Usage: userutil
while (1)
echo "AVAILABLE OPTIONS"
echo "*******************"
echo "[1] Display today's date"
echo "[2] How many people are logged on"
echo "[3] How many user accounts exist"
echo "[4] Exit"
echo "Enter Your Choice [1-4]:"

Karkha.
69 com

userutil shell script 2 of 2
set answer = $<
switch ($answer)
case "1":
echo `date`; breaksw
case "2":
echo `users | wc -w` users are logged in
breaksw
case "3":
echo `cat /etc/passwd | wc -l` users exists
breaksw
case "4":
echo "BYE"
break
breaksw
endsw
end # end of while

Karkha.
70 com

Advanced C Shell Programming
Quoting
Here
Debugging
Trapping Signals

Functions ?
calling other scripts
exec, source, eval

Karkha.
71 com

Quoting for marking a section of a
mechanism
command for special processing:

command substitution: `...`
double quotes: “…“
single quotes: ‘…‘
backslash:

Karkha.
72 com

Doublebreakup of string into words
prevents
quotes
turn off the special meaning of most wildcard
characters and the single quote
$ character keeps its meaning
! history references keeps its meaning

Examples:
echo "* isn't a wildcard inside quotes"
echo "my path is $PATH"

Karkha.
73 com

Single quotes and command
wildcards, variables
substitutions are all treated as ordinary text
history references are recognized

Examples:
echo '*'
echo '$cwd'
echo '`echo hello`'
echo 'hi there !'

Karkha.
74 com

backslash
backslash character
treats following character literally

Examples:
echo $ is a dollar sign
echo is a backslash

Karkha.
75 com

Debugging Scripts
% csh –n scriptname
parse commands but do not execute them

% csh –v scriptname
Display each line of the script before execution

% csh –x scriptname
Displays each line of the script after variable
substitutions and before execution

can also be added to shebang line !
Karkha.
76 com

Calling other scripts
as subshell, via:
csh scriptname
scriptname

subshell does not see current shell’s variables
subshell sees current environment variables

Karkha.
77 com

Karkha unix shell scritping

More Related Content

What's hot (20)

Viewers also liked (20)

Similar to Karkha unix shell scritping (20)

Recently uploaded (20)

Karkha unix shell scritping

Editor's Notes