Unix/Linux Shell Decision Making Lab
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Unix/Linux Shell Decision Making Lab

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Questions and Answers

What does the operator '-eq' signify in relation to two operands?

  • They are equal. (correct)
  • The left operand is less.
  • The left operand is greater.
  • They are not equal.

    • Which operator would return true if the left operand is less than the right operand?

  • -lt (correct)
  • -ge
  • -ne
  • -eq

    • If variable 'a' holds 10 and variable 'b' holds 20, which expression is true when using the '-ne' operator?

  • $a -gt $b
  • $a -ge $b
  • $a -ne $b (correct)
  • $a -eq $b

    • Which operator checks if the left operand is greater than or equal to the right operand?

    <p>-ge</p> Signup and view all the answers

    Why is it important to place conditional expressions inside square braces?

    <p>To ensure proper evaluation.</p> Signup and view all the answers

    Which operator would evaluate to true when comparing if variable 'a' is less than variable 'b'?

    <p>-lt</p> Signup and view all the answers

    What is the result of the expression '[ $a -ge $b ]' if 'a' holds 10 and 'b' holds 20?

    <p>False</p> Signup and view all the answers

    When would the operator '-ne' return false?

    <p>When both operands are equal</p> Signup and view all the answers

    Which expression correctly checks if the values of 'a' and 'b' are not equal?

    <p>[ $a -ne $b ]</p> Signup and view all the answers

    Which of the following conditions would be true for the expression '[ $a -lt $b ]'?

    <p>a is less than b</p> Signup and view all the answers

    Study Notes

    Overview of Shell Decision Making

    • Focus on using conditional statements for programming in Unix/Linux shell.
    • Emphasis on understanding various shell operators and their applications.

    Shell Operators

    • Different types of operators supported by the Bourne shell include:
      • Arithmetic Operators for calculations.
      • Relational Operators for numeric comparisons.
      • Boolean Operators for logical operations.
      • String Operators for manipulating strings.
      • File Test Operators to check file properties.

    Arithmetic Operators

    • Basic arithmetic operations handled via external programs like awk or expr.
    • Examples:
      • Addition: expr $a + $b outputs 30 if a=10 and b=20.
      • Subtraction: expr $a - $b outputs -10.
      • Multiplication: expr $a \* $b outputs 200.
      • Division: expr $b / $a outputs 2.
      • Modulus: expr $b % $a outputs 0.

    Conditional Expressions

    • All comparison expressions must be enclosed in square brackets with spaces.
    • Example of correct usage: [ $a == $b ] versus incorrect: [$a==$b].

    Relational Operators

    • Specific to numeric values; do not work accurately for strings unless numeric values are used.
    • Operators include:
      • -eq: Checks for equality (false if equal).
      • -ne: Checks for inequality (true when operands differ).
      • -gt: Greater than comparison.
      • -lt: Less than comparison.
      • -ge: Greater than or equal to comparison.
      • -le: Less than or equal to comparison.

    Syntax and Usage

    • All conditional expressions must be properly formatted within brackets to ensure valid evaluation during execution.

    Overview of Shell Decision Making

    • Focus on using conditional statements for programming in Unix/Linux shell.
    • Emphasis on understanding various shell operators and their applications.

    Shell Operators

    • Different types of operators supported by the Bourne shell include:
      • Arithmetic Operators for calculations.
      • Relational Operators for numeric comparisons.
      • Boolean Operators for logical operations.
      • String Operators for manipulating strings.
      • File Test Operators to check file properties.

    Arithmetic Operators

    • Basic arithmetic operations handled via external programs like awk or expr.
    • Examples:
      • Addition: expr $a + $b outputs 30 if a=10 and b=20.
      • Subtraction: expr $a - $b outputs -10.
      • Multiplication: expr $a \* $b outputs 200.
      • Division: expr $b / $a outputs 2.
      • Modulus: expr $b % $a outputs 0.

    Conditional Expressions

    • All comparison expressions must be enclosed in square brackets with spaces.
    • Example of correct usage: [ $a == $b ] versus incorrect: [$a==$b].

    Relational Operators

    • Specific to numeric values; do not work accurately for strings unless numeric values are used.
    • Operators include:
      • -eq: Checks for equality (false if equal).
      • -ne: Checks for inequality (true when operands differ).
      • -gt: Greater than comparison.
      • -lt: Less than comparison.
      • -ge: Greater than or equal to comparison.
      • -le: Less than or equal to comparison.

    Syntax and Usage

    • All conditional expressions must be properly formatted within brackets to ensure valid evaluation during execution.

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    Related Documents

    lab9.docx

    Description

    This lab focuses on understanding conditional statements and the various operators supported by the Unix/Linux shell. Students will learn how to implement decision-making processes in shell scripts to execute the correct actions. Key concepts will be reinforced through practical applications in the lab.

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