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Unix

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  • 1. HSBC Global Technology UNIX -Kirtikumar Shinde
  • 2. Topics
    • 1. Introduction
    • Unix Filesystem
    • File Permissions
    • Advanced Commands
    • Shell
    • Shell Programming
    • AWK
    • My Learnings
    • Questions?
  • 3. Introduction
    • Multi-user and Multitasking OS
    • Mostly Written in C at Bell Labs
    • Most of the servers are on Unix
    • Unix Flavors
      • Solaris
      • HP
      • AIX
      • Linux
    • Current DS Server – Which Unix?
  • 4. Introduction
    • Architecture
  • 5. Unix File System
    • An upside-down Tree
    / etc bin export home user ad s3910120 dev tmp exam.txt work hobby.c proj1 date cal . . . . . . . . . . . . . . . . . . . . . . . . .
  • 6. File permissions
    • Changing permissions
      • chmod g+w empl.txt
      • chmod 754 empl.txt
    • Changing ownership
      • chown gcdv_dev empl.txt
    • Changing group
      • chgrp develp empl.txt
    reading others group owner 1 0 0 1 0 1 1 1 1 - r - r - x r x w execution writing
  • 7. Advanced Commands
    • Sort
      • Sorts the contents of a file .
        • sort [-b f n r o t] [file name(s)]
      • Takes the contents of a file(s) and displays it in sorted order.
      • Flags:
        • -b ignores blanks
        • -f change all lower case letter to upper case before comparing
        • -n numeric sort
        • -r reverse usual order
        • -o sends output of command to some file
        • -t field delimiter
      • E.g. To sort the Emp.txt on 2 nd field in reverse order
      • $sort -t, -n -r +2 Emp.txt
  • 8. Advanced Commands
    • grep
      • Searches a file for pattern .
        • grep [-c i l v] <pattern> [file name(s)]
      • Takes the contents of a file(s) and displays it in sorted order.
      • Flags:
        • -c displays count of matching lines.
        • -i ignore the case while searching
        • -l lists the names of files that matches pattern
        • -v displays all lines that don’t contain the pattern
      • E.g. To display all lines in the ‘Emp.txt’ that match either the abc or xyz string:
      • $grep &quot;abc|xyz&quot; Emp.txt
  • 9. Advanced Commands
    • tar
      • Compression and decompression of files.
        • tar -(x|c) [ v f r] <tarfile> [file name(s)]
      • Flags:
        • -x extract from file.
        • -c create new extract file.
        • -v displays list files
        • -f name of file follows
        • -r append to old extract.
      • E.g .
        • To compress file Emp.txt $tar -cvf Emp.tar Emp.txt
        • To decompress file Emp.tar $tar -xvf Emp.tar
  • 10. Shell
    • Command interpreter that waits for commands, executes them and displays the results
    • Bourne shell
      • Developed by Steve Bourne at AT&T
    • Korn shell
      • Developed by David Korn at AT&T
    • C-shell
      • Developed by Bill Joy for Berkeley Unix
  • 11. Shell
    • Shell works as follows:
      • Shell displays a prompt.
      • You type in a command.
      • You press the return key.
      • The shell interprets the commands typed and tries to find the correct programs to run.
      • The kernel runs the requested programs and returns the results to the shell.
      • The shell displays the command prompt again
  • 12. Shell
    • Which Shell I am in ?
      • finger –m myusername
    • Know your shell – Korn Shell – its features
      • Aliases – It allows shorthand for commands.
      • Command history – Lets you recall previously entered commands.
      • Command line editing – Allows us to edit commands vi style.
      • Integrated programming features – It enables common programming tasks to be done cleanly & without creating extra processes.
      • Support regular expressions.
      • Advanced I/O features – Ability to carry out two way communication with concurrent processes.
      • Increased speed of shell code execution.
      • Has highly robust security features.
  • 13.
    • Shell system variables
      • PATH = Defines path shell must search in order to execute any command or file.
      • HOME = Indicates default working directory of the user.
      • PS1 = System prompt 1.
      • PS2 = System prompt 2, default value is “>”.
    Shell
  • 14. UNIX S hell Programming
    • Shell Script (Shell Procedure)
      • A program written in shell programming language is known as a shell script or shell procedure.
    • Shell Programming Language
      • The shell programming language is a command language with a lot of features common to many computer programming languages, including the structured language constructs: sequence, selection, and iteration.
    • Command Languages
      • Command languages are interpreted language s
      • It allows then use of Unix commands in scripts
  • 15. UNIX S hell Programming
    • Shell scripting keywords.
      • Please Note : Script variables shouldn’t be same as keywords.
        • Looping constructs, to be discussed in coming slides.
        • set, unset
        • Readonly
        • Exit
        • Ulimit
        • Umask
  • 16. UNIX S hell Programming
    • Create - Simple Hello World shell script.
        • #!/bin/sh
        • echo &quot;Hello World“
    • Make Files Executable
        • $ chmod 777 HelloWorld.sh
    • Execute the shell script
      • Observe the output ‘Hello World’ will be between two command prompts.
        • $ HelloWorld.sh
  • 17. UNIX S hell Programming
    • Assignments
      • Value assignments.
      • String assignment –
        • var=“Your Name”
        • Think if not within double quotes.
        • $echo $var
        • think if not $
        • Making variable readonly. a=50 readonly a
  • 18. UNIX S hell Programming
    • echo and Escape Characters
      • Display strings as “printf” in C
      • The echo command recognizes escape characters. Escape characters all start with the backslash ( ), and you can use them as part of the echo command argument string.
      • E.g.
        • $ echo “ Hello ”
  • 19. UNIX S hell Programming
    • Passing parameters to a Shell script
      • Consider Welcome.sh, & we are sending name as parameter to a Shell Script. Welcome.sh Vikram
      • think If you want to send First name & Last name as one parameter. In above case 0 th parameter value considered will be script name. 1 st parameter value considered will be name, i.e.Vikram.
    • Accessing parameters in a Shell script
      • Parameter to a shell script starts from index 1. Its value is retrieved by using $1 & so on. … Think how you will access parameter beyond 9 th parameter.
  • 20. UNIX S hell Programming
    • Shell Positional Variable
      • $0 : command itself
      • $1 : first parameter
      • $n : nth parameter
      • $# : no. of parameters
      • $? : exit status of last command executed
      • $* : all parameters
      • $$ : process number of shell
      • $! : PID of last background process
  • 21. UNIX S hell Programming
    • if-then and if-then-else
      • The if-then Construct
        • if [ condition ]
        • then
        • true-commands
        • f i
      • The if-then-else Construct
        • if [ condition ]
        • then
        • true-commands
        • else
        • false-command(s)
        • fi
  • 22. UNIX S hell Programming
    • if-then-elif
        • if [ condition1 ]
        • then
        • commands_1
        • elif [ condition2 ]
        • then
        • commands_2
        • else
        • commands_n
        • fi
  • 23. UNIX S hell Programming
    • test Command
      • The test command is a built-in shell command that evaluates the expression given to it as an argument and return true if the expression is true, if otherwise, false.
      • You can use square brackets ( [ ] ) instead of the word test.
      • Example
        • if test $str1 = $str2 then echo “Something” fi
        • if [$str1 = $str2] then echo “Something” fi
  • 24. UNIX S hell Programming
    • Logical Operators
      • -a AND Operator
      • -o OR Operator
      • ! NOT Operator
    • Numeric Test Operators
      • -eq Is number1 equal to number2 ?
      • -ne Is number 1 not equal to number2 ?
      • -gt Is number1 great than number2 ?
      • -ge Is number1 great than or equal to number2 ?
      • -lt Is number1 less than number2 ?
      • -le Is number1 less than or equal to number2 ?
    • E.g
      • if test $var –lt 10 then echo “Something” fi
  • 25. UNIX S hell Programming
    • String Test Operators
      • string1 = string2 Does string1 match string2?
      • string1 != string2 Does string1 not match string2?
      • -n string Does string contain characters?
      • -z string Is string an empty string?
    • E.g.
      • if test $str1 = $str2 then echo “Something” fi
      • Think if no space on both sides of an operator
  • 26. UNIX S hell Programming
    • File Test Operators
      • -s file True if File size is greater than 0
      • -f file True if File exists & not a directory
      • -d file True if file exists & is a directory file.
      • -r file True if file exists & you have read permission on it.
      • -w file True if file exists & you have write permission on it.
      • -x file True if file exists & you have execute permission on it.
    • E.g
      • if [ –f $filename ] then echo “Something” fi
      • Think if no space on both sides of an option.
  • 27. UNIX S hell Programming
    • The expr Command
      • Arithmetic Operators
      • + : Addition operator
      • - : Subtraction operator
      • / : Division operator
      • * : Multiplication operator
      • % : Remainder operator
    • Expressions
      • Arithmetic expression a=`expr $a + $b` … think if no space both the sides of + & space both the sides of =.
      • Floating point arithmetic expression a=`expr $a + $b | bc `
      • String expression path=$path1”/”$path2
  • 28. UNIX S hell Programming
    • While Loop
      • while [ condition ]
      • do
      • command(s)
      • done
    • For Loop
      • for variable in list-of-value
      • do
      • command(s)
      • done
  • 29. AWK
    • Introduction to awk.
      • awk is a programming language designed to search for, match patterns, and perform actions on files. awk programs are generally quite small, and are interpreted.
      • awk scans input lines one after the other, searching each line to see if it matches a set of patterns or conditions specified in the awk program. For each pattern, an action is specified. The action is performed when the pattern matches that of the input line.
      • Sample awk command: awk ‘/pattern/’’{print $0}’ file1
  • 30. My Learnings
    • When I will go for Shell scripting.
      • Automating my regular tasks.
      • Customizing my work environment.
      • Task is pretty simple
    • When I will avoid Shell scripting .
      • It needs interaction with multiple applications.
      • Problem is relatively complex involves more than one tool.
      • Lookups or finding data .
  • 31.
    • Questions ?
  • 32. Thank You

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