Shell Programming Concepts
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Questions and Answers

What will be the output if the value of val is 50 in the nested if statement?

  • That's a small number (correct)
  • That's a large number
  • Even number
  • Not eligible

    • Which boolean operation is used to check multiple conditions simultaneously in the provided examples?

  • xor (^)
  • and (&&) (correct)
  • or (||)
  • not (!)

    • In the if elif else structure, what will the output be if val equals 17?

  • You are a minor
  • You may enroll for a voter (correct)
  • You are not eligible
  • You are a voter

    • What will the following for loop output: for i in {1..3}; do echo -n "$i "; done?

    <p>1 2 3 (B)</p> Signup and view all the answers

    What will be the output of the for loop that iterates from 0 to 10 with increments of 2?

    <p>Welcome 0 times Welcome 2 times Welcome 4 times Welcome 6 times Welcome 8 times Welcome 10 times (C)</p> Signup and view all the answers

    What does the variable $HOSTNAME represent?

    <p>The name of the current computer (C)</p> Signup and view all the answers

    Which variable would you check to find the shell's version number?

    <p>$BASH_VERSION (B)</p> Signup and view all the answers

    What does the variable $CDPATH do?

    <p>Specifies the search path for the cd command (A)</p> Signup and view all the answers

    Which variable shows the default timeout value for input during the read command?

    <p>$TMOUT (C)</p> Signup and view all the answers

    What does the $PATH variable indicate?

    <p>The directories to look for executable commands (A)</p> Signup and view all the answers

    Which variable indicates the current user's home directory?

    <p>$HOME (D)</p> Signup and view all the answers

    What is the purpose of the $TERM variable?

    <p>Specifies the current terminal type being used (A)</p> Signup and view all the answers

    Which command would you use to view the current value of $HISTSIZE?

    <p>echo $HISTSIZE (D)</p> Signup and view all the answers

    What command is used to set the default text editor in the shell?

    <p>export EDITOR=/usr/bin/vim (D)</p> Signup and view all the answers

    Which operator checks if a string is empty in a shell script?

    <p>-z STRING (D)</p> Signup and view all the answers

    How would you obtain the result of adding two integer variables in a shell script?

    <p>Val=<code>expr $a + $b</code> (A)</p> Signup and view all the answers

    In an if statement, which condition checks if a value is greater than 100?

    <p>if [ $val -gt 100 ] (D)</p> Signup and view all the answers

    What does the operator '-e FILE' check in a shell script?

    <p>FILE exists (B)</p> Signup and view all the answers

    Which command is used to display the current working directory in a shell script?

    <p>pwd (B)</p> Signup and view all the answers

    How can you read multiple inputs into separate variables in a shell script?

    <p>read a b c (D)</p> Signup and view all the answers

    What is the purpose of the command 'echo $DISPLAY' in the shell?

    <p>Print the name of the X display (C)</p> Signup and view all the answers

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    Flashcards

    BASH_VERSION

    Holds the version of the current bash instance.

    HOSTNAME

    The name of your computer.

    CDPATH

    The search path for the cd command.

    HISTFILE

    The name of the file where command history is saved.

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    HISTSIZE

    Number of commands to remember in command history.

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    HOME

    The home directory of the current user.

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    IFS

    The Internal Field Separator used for word splitting.

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    PATH

    A colon-separated list of directories for command search.

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    export

    A command to set environment variables in the shell.

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    SHELL

    The default login shell for the user, specifies the command interpreter.

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    DISPLAY

    Environment variable that defines the X server display to use.

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    expr command

    Used to evaluate expressions and perform integer arithmetic.

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    if statements

    Used to execute commands based on conditions being true or false.

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    -gt operator

    Tests if one integer is greater than another.

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    -e FILE

    Checks if a given file exists regardless of its type.

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    -d FILE

    Tests if a file is a directory.

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    Nested If Statements

    If statements within another if statement, for multiple conditions.

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    If Else Statements

    A control structure where one action occurs if a condition is true and another if it's false.

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    If Elif Else Statements

    Extends if else with additional conditions using elif for multiple scenarios.

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    Boolean Operations

    Combining conditions using logical operators like AND (&&) and OR (||).

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    For Loop

    A loop that iterates over a sequence or range, repeating actions for each item.

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    Study Notes

    Shell Programming

    • This presentation covers shell programming concepts.

    • It outlines user-defined and system-defined variables.

    • System variables are predefined by the shell and hold information about the system environment

    • Examples of system variables include:

      • $BASH_VERSION: Holds the version of the bash shell.
      • $HOSTNAME: Displays the computer's name.
      • $CDPATH: Shows the search path for cd command.
      • $HISTFILE: The file name for saving command history.
      • $HISTFILESIZE: The maximum number of lines in the command history file.
      • $HISTSIZE: The maximum number of commands remembered by shell history; default is 500.
      • $HOME: The home directory of the current user.
      • $IFS: The internal field separator. Default is , used for splitting strings.
      • $LANG: Locale category variable.
      • $PATH: Directory search path for shell commands.
      • $PS1: User's prompt setting.
      • $TMOUT: The shell timeout setting for input. A shell with a timeout setting will log out if no command is entered within the specified time limit.
      • $TERM: User's login terminal type.
      • $SHELL: Path to the shell.
      • $DISPLAY: X display name.
      • $EDITOR: Default text editor.

    • User-defined variables are created by the user for specific tasks.

    • Example of user defined variables:

      • a=50 assigns a value to the variable a
      • read abc: Takes user input for variable abc.
      • read -a name: Takes array input for variable name.
      • `echo "name[0]{name[0]} name[0]{name[1]} ${name[2]}": Displays array elements.

    Expressions

    • Using command substitution for expressions
    • Example for adding numbers:
      • val=expr a+a + a+b`
    • Example for multiplying numbers:
      • val=expr a∗a * a∗b`
    • Example for adding integer/floating-point numbers:
      • val=echo a+a + a+b | bc -l`
    • bc: Basic calculator.

    If Statements

    • The if statement is used for conditional execution of commands.
    • Structure:
      • if [ <condition> ]
      • then followed by the commands to execute if the condition is true
      • fi marks the end of the if block
    • Example: verifying if a value is greater than 100
      • if [ $val -gt 100 ]
      • then
      • echo "Large number"
      • fi

    Nested If Statements

    • Using if statements within other if statements.
    • Example checking if a value is both less than 100 and even:
      • if [ $val -lt 100 ]
        • then
          • if [ expr $val % 2 -eq 0 ]
            • then
              • echo "Even and small number"

    If-Else

    • Executes different blocks of commands based on condition.
    • Structure:
      • if [ <condition> ]
      • then followed by commands if true
      • else followed by commands if false
      • fi marks end
    • Example: check if value is less than 100, display one message, otherwise display another
      • if [ $val -lt 100 ]
        • then
          • echo "Small number"
        • else
          • echo "Large number"
        • fi

    If-Elif-Else

    • Allows for multiple conditions.
    • Structure: -if [ <condition1> ]
      • then followed by commands for condition1
      • elif [ <condition2> ]
        • then followed by commands for condition2
      • else executed if no condition matches
      • fi marks end
    • Example: age-based eligibility check
      • if [ $val -gt 18 ]
        • then echo "Voter"
      • elif [ $val -eq 17 ]
        • then echo "Enroll for voter"
      • else echo "Not eligible"
      • fi

    Boolean Operators

    • Combining conditions using && (and) and || (or).
    • if [ <condition1> && <condition2> ]
      • Executions if both condition1 and condition2 are true.
      • if [ $val -lt 25 ] && [ $val -gt 20 ]

    Looping Constructs

    • while loop: Executes a block of code repeatedly as long as a condition is true.
    • for loop: Iterates over a list of items.
    • until loop: Repeats a block until a condition becomes true.

    Case Statements

    • case <expression> in
    • pattern 1) <commands>;;
    • pattern 2) <commands>;;
    • esac
    • Example: checks various states of a variable
      • case $x instart) <commands>;;stop) <commands>;;*) <commands>;;

    Functions

    • Reusable blocks of code.
    • function_name() { code; }
    • f1() and f2(): nested functions call example
    • Passing parameters using $1, $2, etc. for arguments.

    Assignment Questions

    • Various programming tasks are given.

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    Related Documents

    Shell Programming Notes PDF

    Description

    This quiz explores key concepts in shell programming, focusing on user-defined and system-defined variables. Participants will learn about essential system variables, such as $BASH_VERSION, $HOSTNAME, and more, which hold crucial information about the shell environment. Develop your understanding of how these variables influence shell operations and commands.

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