1. Operating Systems Shell Commands & Script Programming
Kyung Eun Park, D.Sc.
Department of Computer and Information Sciences
Towson University

2. Contents
Linux Shell Scripting
PowerShell

3. Credits FreeOS Software Construction (J. Shepherd)
Operating Systems at Cornell (Indranil Gupta, Niranjan Nagarajan)
Programming in C (Brian W. Kernighan, Bell Lab.)

4. Shell Script Basics Write script program using any editor
$ vi myShell
Make is executable
$ chmod 755 myShell
$ chmod +x myShell
Execute the script
$ bash script_name
$ sh script_name
$ ./script_name

5. First Shell Script
$ vi shellscript #  comment # First Shell Script # clear  clear the screen echo “Hello Shell Script”  print message $ chmod +x shellscript  set execution permission $ ./shellscript

6. System Variables in Shell
BASH=/bin/bash HOME=/home/tiger LOGNAME=tiger OSTYPE=linux-gnu PATH=/usr/lib64/qt- 3.3/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin:/opt/jdk1. 8.0_101/bin:/home/tiger/bin PWD=/home/tiger/tmp SHELL=/bin/bash USERNAME=tiger

7. Definition of User Defined Variables (UDVs)
Syntax: variable_name=value $ num=10 $ name=Park $ vehicle=Car Rules: - no spaces on either side of the equal sign - case-sensitive - to print: $ echo $NAME_OF_VARIABLE

8. Shell Arithmetic Operations
Syntax:
expr op1 operator op2
$ expr 1 + 3
$ expr 5 - 2
$ expr 50 / 5
$ expr 20 \*  Use \* instead of * (used as wildcard)
$ expr 1032 % 10
$ echo `expr `
$ echo $?  Prints exit status

9. Read Statement Syntax: read variable1, variable2, … variable
$ cat > sayName #
echo “Please type your name”
read name
echo “Hello $name!”  CTRL-D to save
$ chmod +x sayName
$ ./sayName
Please type your name
Brad
Hello Brad!

10. Wild Cards
* : matching any string or group of characters (0 or more) ? : matching any single character […] : matching any one of the enclosed characters $ ls [abc]*  show all files beginning with letters a, b, c $ ls ?  show all files whose names are 1 character long $ ls data*.txt  show all files whose names begin with data $ ls data?.txt  show all files whose names are 5 character long and begin with data

11. Variables and Operations (1)
Variable definition: x with value 10 and print it on screen with echo and $
$ x=10
$ echo $x
Variable definition: street with value YR and print it on screen
$ street=YR
$ echo $street
Operation
$ echo  print: 7800 not 807 as a string concatenation
For math operations: use expr, space between number and operator
$ expr  print: 7800

12. Variables and Operations (2)
Variable assignments
$ num1=30
$ num2=6
Assignment with expression
$ result=`expr 30 /6`
$ echo $result
String substitution
$ echo “The address is $street 7800”
Parameter substitute: command execution first
$($ echo `expr `)  Parameter substitution with backquotes

13. Shell Commands
Command in backquotes is executed first and the output is used with other commands
$ pwd
$ cp /home/kpark/os/shell.sh `pwd`  shell.sh is copied to the working directory
$ cp /home/kpark/os/shell.sh  compare this with above command
Examples
$ echo “Today is `date`”
$ echo $HOME
grep command with ps command to find out a process
$ ps aux | grep elasticsearch  the process you want to search for
$ kill PID_of_the_process

14. Shell Built in Variables
$# : number of command line arguments $* : all arguments to shell : same as above $- : options supplied to shell $$ : PID of shell $! : PID of last started background process (started with &)

15. Example Script with Shell Built in Variables
$ vi demo #!/bin/sh # # Script that demos, command line arguments echo “Total number of command line argument : $#” echo “$0 is script name” echo “$1 is first argument” echo “$2 is second argument” echo “All of them are: $* or

16. Standard I/O Redirection: <, >, >>
Syntax:
command > filename
$ ls > tmpfile : create new file, tmpfile, send the result of ls command to it
$ history >> tmpfile : attach the result of history to tmpfile
$ date >> tmpfile
$ cat > months
Jan
Feb
Mar
Apr
Press CTRL-D to save
$ sort < months > sorted
$ cat sorted

17. Pipes
Connect the output of one program to the input of another program without any temporary file
$ ls | more
$ who | sort
$ who | sort > users
$ who | grep tiger

18. Process Related Command
$ ps $ kill $ ps aux, ps –ag $ ps ax | grep sshd $ top : currently running processes and information such as memory and CPU usage $ pstree

19. Decision Making if…fi
Shell uses 0 for true and non-zero value for false
Syntax:
if condition
then
commands … fi
e.g.
if test $1 -gt 0
echo “$1 number is positive”
else
echo “$1 number is negative”

20. if-else-fi Syntax: e.g. if condition then commands … else fi if cat $1
echo –e “\n\nFile $1, exists”

21. Numeric Operators with test Command
Using test command -eq -ne -lt -le -gt -ge $ cat > ispositive  write a shell script using cat #!/bin/sh if test $1 –gt 0 then echo “$1 number is positive” fi $ chmod 755 ispositive $ ./ispositive 50

22. String Comparison with test Command
Using test command string1 = string2 string1 != string2 string1 -n string1 -z string1 $ cat > equals  write a shell script using cat #!/bin/sh if test $1 –eq $2 then echo “$1 equals to $2” fi $ chmod 755 equals $ ./equals julie Julia

23. File and Directory Processing with test Command
Using test command -s file -f file -d dir -w file -r file -x file $ cat > filetest  write a shell script using cat #!/bin/sh if test –f $1 then echo “File $1 exists” fi $ chmod 755 filetest $ ./filetest names

24. Logical Operators with test Command
Using test command ! expression expression1 –a expression2 expression1 –o expression2 $ cat > logictest  write a shell script using cat #!/bin/sh if test $1 –a $2 then echo “Both $1 and $2 are TRUE” fi $ chmod 755 logictest $ ./logictest 1 1

25. Argument Checking
$ cat > add2numbers if [ $# -ne 2] then echo “Error : Two numbers to be added are needed.” echo “Usage : $0 number1 number2” fi ans=`expr $1 + $2` echo “Sum is $ans”  CTRL-D to save $ chmod 755 add2numbers $./add2numbers  Error notification with correct usage will be printed $./add2numbers

26. Functions
Syntax: function-name () { commands… } $ SayHello() { echo “Hello $LOGNAME” return $ SayHello

27. PowerShell
A task automation and configuration management framework from Microsoft
Designed especially for system administrators and built on top of the .NET Framework common language runtime (CLR) and the .NET Framework
Accepts and returns .NET Framework objects
Components
Command-line shell
Scripting language (built on the .NET Framework)
Interactive prompt and a scripting environment
Provides full access to COM and WMI
Administrators can perform administrative tasks on both local and remote Windows systems as well as remote Linux systems and network devices
Currently, open-source and cross-platform (since Aug. 18, 2016)

28. History of PowerShell Microsoft’s command-line interface tool (shell)
Cmd.exe and COMMAND.COM
Command line interpreter for basic commands
Separate console application can be executed from the shell
Script language support in the form of batch files for automating various tasks
Monad (Microsoft Shell or MSH) in 2002
Renamed Windows PowerShell as a component of Windows in 2006
On Aug. 18, 2016, made PowerShell open-source and cross-platform for Windows, OS X, CentOS and Ubuntu  PowerShell Core for .NET Core

29. Cmdlets
Windows PowerShell introduces the concept of a cmdlet (pronounced “command-let”)
Simple, single-function command-line tool built in the PowerShell environment with more than one hundred basic core cmdlets
Verb-Noun naming pattern, such as Get-ChildItem: self-descriptive
Objects or collections as the output results of cmdlets  used in a pipeline
Cmdlets are specialized .NET classes instantiated by the PowerShell runtime
Modules: portable version of Cmdlets in PowerShell V2

30. Pipeline Piping the output of cmdlet to another cmdlet as input
Use ‘|’ operator
The chain of cmdlets stages executes within the PowerShell runtime.
They are structured .NET objects rather than byte streams
.ToString() method to retrieve the text representation of the PowerShell objects

31. Windows PowerShell Integrated Scripting Environment (ISE)

32. Scripting
PowerShell includes a dynamically typed scripting language for implementing complex operations using cmdlets
Script language includes:
Variables: prefixed with ‘$’, assigned any value or objects output of cmdlets
Strings: enclosed in single quotes or in double quotes
$args: array of all the command line arguments passed to a function from the command line
$_: current object in the pipeline
Functions; using function keyword, functions are created:
Branching: if-then-else
Loops: while, do, for, foreach
Structured error/exception handling: caught using try … catch construct
Closures/lambda expressions
name value1 value2
name –Param1 value1 –Param2 value2
function name ($Param1, $Param2) {
Instructions }

33. Running PowerShell Start Windows PowerShell by typing powershell or
Start  PowerShell  Windows PowerShell

34. PowerShell Cmdlets Commands
Get-Help
Get-Service

35. Get-Service | Get-Member

36. Cmd.exe and Unix Commands available inside Windows PowerShell
cat, cd, chdir, clear, cls, copy, del, diff, dir, echo, erase, h, history, kill, lp, ls, mount, move, popd, ps, pushd, pwd, r, ren, rm, rmdir, sleep, sort, tee, type, write
Get-Alias ps