Shell Scripting Essentials

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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

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=_______.

value1 Signup and view all the answers

Match the shell command with its expected output:

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 "The name $name sounds familiar!" = Interprets and displays the value of name with a message Signup and view all the answers

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

John* Signup and view all the answers

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

False Signup and view all the answers

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

No timeout for shell inactivity Signup and view all the answers

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

The name of the script being executed Signup and view all the answers

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

True Signup and view all the answers

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

shift Signup and view all the answers

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

3 Signup and view all the answers

Match the shell script variables with their descriptions:

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

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

True Signup and view all the answers

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

9 Signup and view all the answers

What is a shell script primarily composed of?

Shell commands Signup and view all the answers

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

False Signup and view all the answers

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

$ chmod u+x script_file Signup and view all the answers

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

/bin/bash Signup and view all the answers

Match the shell variable to its corresponding purpose:

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

Which command is used for command substitution in BASH?

$() Signup and view all the answers

Command line arguments can be passed to shell programs.

True Signup and view all the answers

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

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

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

Name of the author 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.

False Signup and view all the answers

What is the purpose of using comments in a script?

To describe the purpose of specific commands Signup and view all the answers

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

loop Signup and view all the answers

Match the following programming concepts with their descriptions:

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 Signup and view all the answers

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

agent007 Signup and view all the answers

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

True Signup and view all the answers

What is a program header?

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

What is the purpose of command substitution in a shell?

To execute a command and substitute its output Signup and view all the answers

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

False Signup and view all the answers

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

read Signup and view all the answers

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

unset Signup and view all the answers

Match the following commands with their purposes:

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 Signup and view all the answers

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

Shifts the command line arguments left by N positions Signup and view all the answers

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

False Signup and view all the answers

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

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

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

chmod u+x script_file Signup and view all the answers

Shell programs are typically stored in ordinary UNIX files.

True Signup and view all the answers

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

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

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

/bin/bash Signup and view all the answers

Match the following shell variable names with their descriptions:

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 Signup and view all the answers

What is a shell variable primarily used for?

To temporarily hold data for use in scripts Signup and view all the answers

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

positional parameters Signup and view all the answers

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

It will list files that start with 'John' when echoed. Signup and view all the answers

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

True Signup and view all the answers

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

No timeout for commands. Signup and view all the answers

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

env Signup and view all the answers

Match the following environmental variables with their descriptions:

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 Signup and view all the answers

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

name='John Doe' Signup and view all the answers

Environmental variables can only be read and not modified.

False Signup and view all the answers

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

John Doe Signup and view all the answers

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

To prevent assignment of new values to variables Signup and view all the answers

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

False Signup and view all the answers

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

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

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

subsequent commands Signup and view all the answers

Match the following shell commands with their purposes:

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

What is the primary function of command substitution?

To replace a command with its output 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.

True Signup and view all the answers

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

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

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

The name of the script being executed Signup and view all the answers

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

True Signup and view all the answers

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

9 Signup and view all the answers

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

@ Signup and view all the answers

Match the shell script command with its description:

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

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

The first argument is removed and the others shift left 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.

True Signup and view all the answers

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

$2 Signup and view all the answers

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

List of all functions used Signup and view all the answers

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

False Signup and view all the answers

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

Repetitive execution 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 ________.

repetitive execution Signup and view all the answers

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

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 Signup and view all the answers

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

Choosing between two possible paths based on a condition Signup and view all the answers

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

False Signup and view all the answers

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

To describe the purpose and functionality of commands Signup and view all the answers

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.

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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!

Shell Scripting Essentials

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Questions and Answers

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

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

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

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

Match the shell command with its expected output:

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

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

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

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

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

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

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

Match the shell script variables with their descriptions:

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

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

What is a shell script primarily composed of?

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

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

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

Match the shell variable to its corresponding purpose:

Which command is used for command substitution in BASH?

Command line arguments can be passed to shell programs.

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

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

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

What is the purpose of using comments in a script?

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

Match the following programming concepts with their descriptions:

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

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

What is a program header?

What is the purpose of command substitution in a shell?

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

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

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

Match the following commands with their purposes:

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

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

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

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

Shell programs are typically stored in ordinary UNIX files.

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

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

Match the following shell variable names with their descriptions:

What is a shell variable primarily used for?

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

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

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

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

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

Match the following environmental variables with their descriptions:

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

Environmental variables can only be read and not modified.

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

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

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

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

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

Match the following shell commands with their purposes:

What is the primary function of command substitution?

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

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

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

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

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

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

Match the shell script command with its description:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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