Shell Scripting Essentials
78 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What command is used to display environmental variables in the shell?

  • echo
  • env (correct)
  • set
  • printenv

The variable assignment in shell requires spaces before and after the equals sign.

False (B)

What will the command 'echo $name' return if 'name' is assigned as 'John Doe'?

John Doe

To assign a variable, you use the syntax variable1=_______.

<p>value1</p> Signup and view all the answers

Match the shell command with its expected output:

<p>echo $name = Displays the value of the variable 'name' echo '$name' = Shows the literal string $name name='John Doe' = Assigns 'John Doe' to the variable 'name' echo &quot;The name $name sounds familiar!&quot; = Interprets and displays the value of name with a message</p> Signup and view all the answers

What will be the output of the command 'echo $name' if 'name' is set to 'John*'?

<p>John* (A)</p> Signup and view all the answers

The command 'name=John' followed by 'name=John Doe' will successfully change the value of 'name'.

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

In the context of shell variables, what does 'TMOUT=0' signify?

<p>No timeout for shell inactivity</p> Signup and view all the answers

What is displayed by the variable $0 in shell scripts?

<p>The name of the script being executed (B)</p> Signup and view all the answers

The variable $@ represents the same information as $*.

<p>True (A)</p> Signup and view all the answers

What command is used to remove the first argument from the list in a shell script?

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

In the command cmdargs_demo a b c, the total number of command line arguments passed is: ____.

<p>3</p> Signup and view all the answers

Match the shell script variables with their descriptions:

<p>$0 = Script name $# = Number of arguments $1 = First argument $@ = All arguments</p> Signup and view all the answers

The command shift 3 removes the first three arguments from the list.

<p>True (A)</p> Signup and view all the answers

How many positional parameters can be accessed directly in a shell script?

<p>9</p> Signup and view all the answers

What is a shell script primarily composed of?

<p>Shell commands (A)</p> Signup and view all the answers

A shell variable can only be read but not written to.

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

What command would you use to make a script file executable?

<p>$ chmod u+x script_file</p> Signup and view all the answers

The command used to run a shell script in the Bourne Shell is $ ____ script_file.

<p>/bin/bash</p> Signup and view all the answers

Match the shell variable to its corresponding purpose:

<p>AUTHSTATE = Authentication state CGI_DIRECTORY = Path for CGI scripts MAIL = User's mailbox path PATH = System command search paths</p> Signup and view all the answers

Which command is used for command substitution in BASH?

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

Command line arguments can be passed to shell programs.

<p>True (A)</p> Signup and view all the answers

What is the significance of the shebang (#!) in a shell script?

<p>It specifies the interpreter that should be used to run the script.</p> Signup and view all the answers

Which of the following elements should be included in a program header for a shell script?

<p>Name of the author (B)</p> Signup and view all the answers

The three basic types of statements for controlling flow in a script are two-way branching, loop statements, and multiway branching.

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

What is the purpose of using comments in a script?

<p>To describe the purpose of specific commands</p> Signup and view all the answers

A ________ statement in programming allows a script to execute commands repeatedly.

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

Match the following programming concepts with their descriptions:

<p>Two-way branching = Conditionally executes one of two branches Multiway branching = Selects one from multiple options based on conditions Repetitive execution = Executes commands multiple times based on a condition Comments = Describes the purpose of code segments</p> Signup and view all the answers

In the provided example script, what is the 'secretcode' variable set to?

<p>agent007 (D)</p> Signup and view all the answers

The 'while' statement continues executing as long as its condition is true.

<p>True (A)</p> Signup and view all the answers

What is a program header?

<p>A section at the beginning of a script that provides metadata about the script.</p> Signup and view all the answers

What is the purpose of command substitution in a shell?

<p>To execute a command and substitute its output (A)</p> Signup and view all the answers

The 'readonly' command allows for the assignment of new values to a variable after it has been defined.

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

What command is used to read one line from standard input and assign it to variables?

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

The command used to remove a variable or function is called ______.

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

Match the following commands with their purposes:

<p>export = Copy current values to every command executed shift = Shift command line arguments to the left readonly = Prevent new assignments to variables set = Display names of all shell variables and their values</p> Signup and view all the answers

What does the 'shift[N]' command do in a shell script?

<p>Shifts the command line arguments left by N positions (D)</p> Signup and view all the answers

The 'set' command can only be used with arguments; it has no functionality without them.

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

What is the purpose of the 'export' command in a shell?

<p>Export the names and current values of the variables to every command executed.</p> Signup and view all the answers

Which command is used to add execute permission to a script file?

<p>chmod u+x script_file (A)</p> Signup and view all the answers

Shell programs are typically stored in ordinary UNIX files.

<p>True (A)</p> Signup and view all the answers

What is the purpose of the shebang (#!) at the beginning of a shell script?

<p>It specifies the interpreter to be used for executing the script.</p> Signup and view all the answers

The command to execute a shell script directly is $ ________ script_file.

<p>/bin/bash</p> Signup and view all the answers

Match the following shell variable names with their descriptions:

<p>HOME = Current user's home directory PATH = List of directories to search for executable commands MAIL = Path to the current user's mail spool PS1 = Primary prompt string in shell</p> Signup and view all the answers

What is a shell variable primarily used for?

<p>To temporarily hold data for use in scripts (D)</p> Signup and view all the answers

What is it called when command line arguments are passed to a shell script?

<p>positional parameters</p> Signup and view all the answers

What will happen if a variable is defined as 'name=John*'?

<p>It will list files that start with 'John' when echoed. (B)</p> Signup and view all the answers

The command 'name='John Doe'' is valid for assigning a variable in the shell.

<p>True (A)</p> Signup and view all the answers

What is indicated by the variable 'TMOUT=0'?

<p>No timeout for commands.</p> Signup and view all the answers

The command to display all environmental variables is '______'.

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

Match the following environmental variables with their descriptions:

<p>USER = The current logged-in user HOME = The home directory of the user SHELL = The path to the shell being used MAIL = Path to the user's mail spool</p> Signup and view all the answers

Which of the following is a correct method for defining a shell variable with spaces?

<p>name='John Doe' (B), name=&quot;John Doe &quot; (C)</p> Signup and view all the answers

Environmental variables can only be read and not modified.

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

What is the output of 'echo $name' if 'name' was set to 'John Doe'?

<p>John Doe</p> Signup and view all the answers

What is the purpose of the readonly command in the shell?

<p>To prevent assignment of new values to variables (D)</p> Signup and view all the answers

The command unset [name-list] can be used to add new variables to the shell.

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

What does the command shift[N] achieve in a shell script?

<p>It shifts the command line arguments N positions to the left.</p> Signup and view all the answers

The export command is used to make variables available to ________ executed from the shell.

<p>subsequent commands</p> Signup and view all the answers

Match the following shell commands with their purposes:

<p>export = Make variables available to child processes read = Read from standard input unset = Remove the variable or function readonly = Prevent reassignment of variable values</p> Signup and view all the answers

What is the primary function of command substitution?

<p>To replace a command with its output (D)</p> Signup and view all the answers

The set command, when executed without any arguments, displays the names of all shell variables and their current values.

<p>True (A)</p> Signup and view all the answers

How can you remove a variable or function defined in the shell?

<p>By using the <code>unset</code> command.</p> Signup and view all the answers

What is displayed by the variable $0 within a shell script?

<p>The name of the script being executed (B)</p> Signup and view all the answers

The $* variable displays the same values as the $@ variable when passing arguments to a shell script.

<p>True (A)</p> Signup and view all the answers

How many command line arguments can you access directly using positional parameters in a shell script?

<p>9</p> Signup and view all the answers

The command line argument that references all the parameters passed is represented by _______.

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

Match the shell script command with its description:

<p>shift = Removes the first argument $@ = Displays all arguments $1 = First argument passed $# = Number of arguments passed</p> Signup and view all the answers

What happens to the arguments after executing 'shift' in a shell script?

<p>The first argument is removed and the others shift left (D)</p> Signup and view all the answers

You can use the command 'shift 3' to remove the first three arguments from the list in a shell script.

<p>True (A)</p> Signup and view all the answers

What command would you use to print the second command line argument in a shell script?

<p>$2</p> Signup and view all the answers

What is NOT included in a program header for a shell script?

<p>List of all functions used (B)</p> Signup and view all the answers

Comments in a shell script are optional and can be omitted without impact.

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

What type of statement allows commands to execute repeatedly in a shell script?

<p>Repetitive execution</p> Signup and view all the answers

The three basic types of statements for controlling flow in a script are: two-way branching, multiway branching, and ________.

<p>repetitive execution</p> Signup and view all the answers

Match the following elements with their purposes in a program header:

<p>File Name = The name of the script file Author = The creator of the script Date Written = The date the script was originally created Purpose = Brief explanation of what the script does</p> Signup and view all the answers

Which of the following best describes 'two-way branching'?

<p>Choosing between two possible paths based on a condition (C)</p> Signup and view all the answers

The while statement in a shell script continues executing as long as its condition is false.

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

What is the purpose of putting comments in a shell script?

<p>To describe the purpose and functionality of commands</p> Signup and view all the answers

Flashcards

Shell Script

A shell program containing shell commands to be executed by a shell, stored in a file.

Shell Variable

A storage location used by users and programmers to hold data temporarily.

Command Substitution

A technique where the output of one command is used as input to another.

Executable Script

A shell script with execute permission enabling direct execution.

Signup and view all the flashcards

Running a Shell Script

Several ways to execute a shell script, including making it executable, using '/bin/bash'.

Signup and view all the flashcards

Read-only Variable

Shell variables whose values cannot be changed.

Signup and view all the flashcards

Control Flow Commands

Commands enabling non-sequential script execution or repeated command execution.

Signup and view all the flashcards

Command-line arguments

Pieces of information given to a shell program when it's run.

Signup and view all the flashcards

Shell Variable Assignment

Assigning a value to a shell variable. No space before or after the equals sign.

Signup and view all the flashcards

Shell Variable Value Retrieval

Accessing the value of a shell variable using the $ symbol. The variable name is inserted at the place of the value.

Signup and view all the flashcards

Quoting Variables (Double Quotes)

Enclosing a variable name within double quotes preserves spaces within the string

Signup and view all the flashcards

Quoting Variables (Single Quotes)

Enclosing a variable name within single quotes prevents variable expansion, treating the variable's name like a literal.

Signup and view all the flashcards

Dollar Sign for Variables

The dollar sign ($) is a critical prefix to represent a shell variable in a shell command.

Signup and view all the flashcards

Shell Variable Names

Names containing special characters are possible. They are used to store and manage data in a command line environment.

Signup and view all the flashcards

Quoting Special Characters

Use quotes around variables containing special characters to prevent incorrect interpretation, for example when there are spaces in the variable contents.

Signup and view all the flashcards

Shell Environment Variables

Variables set within the shell's environment, affecting how the shell operates.

Signup and view all the flashcards

Shell Script Header

Provides essential information about your shell script, like the author, date, purpose, and algorithm.

Signup and view all the flashcards

Two-way Branching

Allows the script to choose between two different paths based on a condition.

Signup and view all the flashcards

Multiway Branching

Provides a choice between multiple execution paths based on several conditions.

Signup and view all the flashcards

Repetitive Execution

Executes one or more commands repeatedly until a specific condition is met.

Signup and view all the flashcards

The test Command

Evaluates a condition and returns a true (0) or false (non-zero) exit status.

Signup and view all the flashcards

The for Statement

Executes a block of code for each item in a list, perfect for iterating.

Signup and view all the flashcards

The while Statement

Repeats a block of code as long as a condition is true.

Signup and view all the flashcards

Program Control Flow Commands

These commands manage the order in which statements in a shell script are executed.

Signup and view all the flashcards

Back Quotes

Enclose a command within back quotes (`) to execute it and replace the command with its output.

Signup and view all the flashcards

Exporting Variables

The export command copies variable values to all child processes spawned from the current shell.

Signup and view all the flashcards

Resetting Variables

The unset command removes a variable or function from the current shell's environment.

Signup and view all the flashcards

Reading From Standard Input

The read command reads a line from standard input (usually your keyboard) and splits it into words, assigning them to variables.

Signup and view all the flashcards

Shifting Arguments

The shift command shifts the positional arguments of a shell script to the left, effectively removing the first argument.

Signup and view all the flashcards

Setting Arguments

The set command modifies the positional arguments of a script. Without arguments, it displays all shell variables and their values.

Signup and view all the flashcards

Special echo Characters

The echo command can use special characters (like for newline, for tab) to format output.

Signup and view all the flashcards

What is the purpose of $0 in a shell script?

$0 represents the name of the shell script being executed. It's the first argument passed to the script, indicating its own filename.

Signup and view all the flashcards

How do you access the number of command-line arguments?

The $# variable holds the total count of arguments passed to the shell script. It represents the number of items supplied when the script is run.

Signup and view all the flashcards

What is the purpose of $@ and $*?

$@ and $* both represent all the command-line arguments passed to the script. However, $@ preserves spaces within individual arguments, while $* treats the arguments as a single string.

Signup and view all the flashcards

What does the shift command do?

The shift command shifts the positional parameters (command-line arguments) to the left. It removes the first argument and re-indexes the remaining arguments. Each argument then takes on the index value of the argument to its left.

Signup and view all the flashcards

How does shift 3 impact arguments?

The shift 3 command removes the first three arguments from the argument list and re-indexes the remaining arguments. The first argument occupies position $1, the second argument occupies $2, and so on.

Signup and view all the flashcards

What is the purpose of $1, $2, $3, etc.?

The numbers starting from $1 represent individual command-line arguments passed to the script. $1 refers to the first argument, $2 to the second, and so on.

Signup and view all the flashcards

What is the purpose of exit 0?

The exit 0 command ends the execution of the current shell script. It signifies that the script ran successfully without errors.

Signup and view all the flashcards

What is the purpose of exit 1?

The exit 1 command also ends the execution of the current shell script, but it signals an error condition. This means the script experienced a failure.

Signup and view all the flashcards

How to make a script executable?

By giving the file execute permission, you allow it to run directly from the command line. This is done using the chmod command.

Signup and view all the flashcards

Read-only Shell Variable

A shell variable whose value cannot be modified after it is initially set. It acts as a constant within the script.

Signup and view all the flashcards

Passing Arguments to a Script

Providing additional data to a shell script when you run it. This data can then be used within the script's commands.

Signup and view all the flashcards

Displaying Shell Variables

Using the set command to list all defined shell variables and their current values, providing a snapshot of the script's environment.

Signup and view all the flashcards

Shell Variable Retrieval

Accessing the value of a shell variable using the $ symbol before the variable name. The variable name is replaced with its stored value when the script is run.

Signup and view all the flashcards

Double Quotes for Variables

Enclosing a variable name within double quotes preserves spaces within the string and allows for variable expansion.

Signup and view all the flashcards

Single Quotes for Variables

Enclosing a variable name within single quotes prevents variable expansion, treating the variable's name like a literal string.

Signup and view all the flashcards

What does env do?

Displays a list of all environment variables currently set in your shell session, including their corresponding values.

Signup and view all the flashcards

What is the purpose of $0?

The $0 variable represents the name of the shell script being executed. It's the first argument passed to the script, indicating its own filename.

Signup and view all the flashcards

What does exit 0 do?

The exit 0 command ends the execution of the current shell script, indicating that the script ran successfully without errors.

Signup and view all the flashcards

What does exit 1 do?

The exit 1 command ends the execution of the current shell script, but it signals an error condition. This means the script experienced a failure.

Signup and view all the flashcards

Program Header

Essential information at the start of a shell script, including the script's name, author, date, purpose, and description of the algorithm used to solve the problem.

Signup and view all the flashcards

What are command-line arguments?

Additional information passed to a shell script when you run it. They are used to customize the script's actions.

Signup and view all the flashcards

How do you access the first argument?

You access the first argument passed to the script using the symbol $1.

Signup and view all the flashcards

What is $0?

The name of the shell script being executed.

Signup and view all the flashcards

What is $#?

The number of arguments passed to the script.

Signup and view all the flashcards

What is shift command?

It moves command-line arguments to the left, effectively removing the first argument.

Signup and view all the flashcards

How does shift affect arguments?

After shift, the second argument becomes the first, the third becomes the second, and so on.

Signup and view all the flashcards

Exporting Environment Variables

The export command makes variables and their values available to all child processes spawned from the current shell.

Signup and view all the flashcards

Special Characters in echo

The echo command can use special characters (like \n for newline, \t for tab) to format output.

Signup and view all the flashcards

Study Notes

Introduction to BASH Scripting

  • Shell scripting introduces the concept of shell programming.
  • Shell programs are executed by a shell.
  • Shell variables are used for reading and writing storage.
  • Command line arguments are passed to shell programs.
  • Command substitution is a concept.
  • Basic coding principles are described.
  • Shell scripts are written and discussed.
  • Commands and primitives are covered.

Shell Script

  • A shell script is a shell program.
  • Shell commands are executed by the shell.
  • This script is stored in a UNIX file.
  • Shell variables provide read/write storage for users and programmers.
  • They are scratch pads for tasks.
  • Program control flow commands define sequential order of execution.

Running a Bourne Shell Script

  • Make the script file executable by adding execute permission.
  • Example command: chmod u+x script_file
  • Run the script using the bash command.
  • Example command: /bin/bash script_file
  • Force the current shell to execute the script in the Bourne Again Shell.
  • Example command: #!/bin/bash

Shell Variables

  • CDPATH contains directory names searched by cd.
  • EDITOR is the default editor for programs like email.
  • ENV contains paths to configuration files.
  • HOME describes the user's home directory.
  • MAIL is the name of the user's mailbox file.
  • MAILCHECK specifies interval for checking the mailbox.
  • PATH contains directories for finding external commands.
  • PPID is the parent process ID.
  • PS1 is the primary prompt, usually $.
  • PS2 is the secondary prompt, typically >.
  • PWD represents the current working directory.
  • TERM is the terminal type.

Read-only Shell Variables

  • $0: Program name.
  • $1-$9: Command line arguments (1-9).
  • $*: All command line arguments (quoted).
  • $@: All command line arguments (individually quoted).
  • $#: Total arguments.
  • $$: Process ID (PID).
  • $?: Exit status of last command.
  • $!: PID of last background process.

Display Shell Variables

  • Shell variables are shown by using set.
  • Variables and their respective values are displayed.

Reading and Writing Shell Variables

  • Assign values to variables using variable1=value1[variable2=value2...variableN=valueN].
  • No spaces before or after the equals signs.

Command Substitution

  • Enclose a command in back quotes to execute and substitute with the output.
  • Example: echo "$(date)"

Exporting Environment

  • Use export to copy variable values to other commands.
  • export name copies the value of name to other commands.
  • Example: name="John Doe"; export name.

Resetting Variables

  • Use unset to reset variables.
  • Remove the variable or function corresponding to the names in the list.
  • Example command: unset name place

Creating Read-Only Defined Variables

  • Use readonly to prevent assignment of new values to variables.
  • This prevents modification.
  • Example use: readonly name place

Reading from Standard Input

  • Use read variable-list to read a line from standard input.
  • Assign words in the line to variables.

Passing Arguments to Shell Scripts

  • shift [N]: Shifts command line arguments N positions to the left.
  • set [options] [argument-list]: Sets values of positional arguments. (set alone displays current variable values).

Special Characters for the echo Command

  • Special characters to use within the echo command, including: \b, \c, \f, \n, \r, \t, \v, \\, \ON.

Passing Arguments to Shell Scripts: Examples

  • Examples demonstrate how to pass arguments to shell scripts.

Comments and Program Headers

  • Use comments to explain sections of code.
  • Include program headers for every script, including file name, author, date written, date modified, purpose and algorithm.

Program Control Flow Commands

  • Used to control the order of program statements.
  • Examples: branching, loops.

The if Statement (Two-way branching)

  • Conditional statements based on an expression.
  • Implement conditional logic in scripts.
  • Syntax: if expressionthencommands fi`.

Operators for the test Command

  • Operators for the test command (or [ ]), including file testing (e.g., -d file, -f file, -r file, -s file, -t [filedes], -w file, -x file) and integer/string testing.

The for Statement

  • for variable [in argument-list] do command-list done: Loops through items in a list.

The while Statement

  • Repeats commands as long as an expression is true.

The until Statement

  • Repeats commands while an expression is false.

The break and continue Statements

  • break: Exits the loop immediately.
  • continue: Skips the rest of the current iteration.

The case Statement

  • Used for multi-way branching.
  • Example use: case "$option" in d|D) date;; 1|L) ls;; esac.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

Bash Scripting Introduction PDF

Description

Test your knowledge with this quiz on shell scripting essentials. From environmental variables to command-line arguments, this quiz covers key concepts and commands you'll encounter while working in the shell. Perfect for beginners and those looking to refresh their skills!

More Like This

Shell Scripting Basics
15 questions

Shell Scripting Basics

HallowedMajesty avatar
HallowedMajesty
Environment Variables in Shell Scripting
10 questions

Environment Variables in Shell Scripting

WonderfulBlessing avatar
WonderfulBlessing
Shell Scripting Basics Quiz
24 questions

Shell Scripting Quiz: Test Your Shell Basics

SupportingPluto avatar
SupportingPluto
LPIC-1 Topic 105: Shells and Shell Scripting
5 questions

LPIC-1 Topic 105: Shells and Shell Scripting

GuiltlessAshcanSchool avatar
GuiltlessAshcanSchool
Use Quizgecko on...
Browser
Open
Browser
Browser