Command-line arguments ($1, $2, ...) in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does $1 represent in a bash script?

$1 is the first command-line argument passed to the script when you run it.

beginner

How do you access the second command-line argument in a bash script?

You use $2 to get the second argument passed to the script.

beginner

What does $# mean in a bash script?

$# gives the number of command-line arguments passed to the script.

intermediate

How can you access all command-line arguments as a single string?

Use $* to get all arguments as one string separated by spaces.

intermediate

What is the difference between $* and $@ in bash?

$* treats all arguments as a single word, while $@ treats each argument as a separate word, especially when quoted.

In a bash script, what does $3 represent?

A The third command-line argument

B The total number of arguments

C The script name

D The first command-line argument

$3 is the third argument passed to the script.

Which variable holds the number of command-line arguments in a bash script?

A $0

B $*

C $@

D $#

$# gives the count of arguments passed.

How do you access the script's own name inside a bash script?

A $#

B $1

C $0

D $@

$0 holds the script's filename.

What is the output of echo "$*" if the script is run with arguments: apple banana cherry?

A applebanana cherry

B apple banana cherry

C apple,banana,cherry

D apple

$* joins all arguments separated by spaces.

Which is true about "$@" in bash?

A It treats each argument as a separate quoted string

B It combines all arguments into one string

C It counts the number of arguments

D It holds the script name

"$@" expands each argument as a separate quoted string.

Explain how to use command-line arguments in a bash script and how to access the first three arguments.

Think about how you run a script with extra words after the script name.

Describe the difference between $* and $@ in bash scripting when handling multiple arguments.

Consider how quoting affects the way arguments are grouped.

Practice

1. What does $1 represent in a bash script?

easy

A. The last command-line argument passed to the script

B. The total number of arguments passed to the script

C. The name of the script file

D. The first command-line argument passed to the script

Solution

1. Step 1: Understand command-line arguments in bash

   In bash scripts, $1 refers to the first argument given after the script name.

2. Step 2: Differentiate from other special variables

   $# is the count of arguments, $0 is the script name, and $@ is all arguments.

3. Final Answer:

   The first command-line argument passed to the script -> Option D

4. Quick Check:

   $1 = first argument [OK]

Hint: Remember $1 is always the first argument after script name [OK]

Common Mistakes:

• Confusing $1 with $# (argument count)
• Thinking $1 is the script name
• Mixing $1 with $0 or $@

2. Which of the following is the correct way to access the third argument in a bash script?

easy

A. $0

B. $2

C. $3

D. $#

Solution

1. Step 1: Recall argument numbering in bash

   Arguments start from $1 for the first, so the third argument is $3.

2. Step 2: Identify incorrect options

   $2 is second argument, $# is count, $0 is script name.

3. Final Answer:

   $3 -> Option C

4. Quick Check:

   Third argument = $3 [OK]

Hint: Count arguments starting at $1, so third is $3 [OK]

Common Mistakes:

• Using $2 instead of $3 for third argument
• Confusing $# with argument value
• Using $0 which is script name

3. What will be the output of this script if run as ./script.sh apple banana cherry?

echo "First: $1"
echo "Second: $2"
echo "Count: $#"

medium

A. First: apple
Second: banana
Count: 3

B. First: apple
Second: cherry
Count: 3

C. First: ./script.sh
Second: apple
Count: 3

D. First: banana
Second: cherry
Count: 2

Solution

1. Step 1: Identify argument values

   Arguments are apple ($1), banana ($2), cherry ($3). Script name is $0.

2. Step 2: Understand output commands

   echo prints $1 as apple, $2 as banana, and $# as 3 (number of arguments).

3. Final Answer:

   First: apple Second: banana Count: 3 -> Option A

4. Quick Check:

   Arguments match output [OK]

Hint: Remember $1, $2 are first and second args; $# is count [OK]

Common Mistakes:

• Mixing script name ($0) with arguments
• Confusing argument order
• Miscounting number of arguments

4. Given this script snippet:

echo "Argument 1: $1"
echo "Argument 2: $2"

What is the error if you run the script without any arguments?

medium

A. Script prints empty lines for $1 and $2

B. No output is printed

C. Script throws a syntax error

D. Script prints the script name instead of arguments

Solution

1. Step 1: Understand missing arguments behavior

   If no arguments are passed, $1 and $2 are empty strings, not errors.

2. Step 2: Check script output

   echo prints "Argument 1: " and "Argument 2: " with nothing after colon.

3. Final Answer:

   Script prints empty lines for $1 and $2 -> Option A

4. Quick Check:

   Missing args = empty $1, $2 [OK]

Hint: No args means $1, $2 are empty, no errors [OK]

Common Mistakes:

• Expecting syntax or runtime error
• Thinking script name prints as argument
• Assuming no output at all

5. You want a bash script to print all arguments passed to it, each on a new line, using only $1, $2, etc. Which approach works best?

hard

A. Use a loop with a counter and access arguments by $1, $2, ... until counter > $#

B. Use shift command in a loop to access each argument and print it

C. Use $0 to print all arguments one by one

D. Use echo $@ to print all arguments on one line

Solution

1. Step 1: Understand how to access all arguments one by one

   Using shift moves arguments left, so $1 becomes next argument each time.

2. Step 2: Compare options

   Use a loop with a counter and access arguments by $1, $2, ... until counter > $# is complex and error-prone; Use echo $@ to print all arguments on one line prints all on one line; Use $0 to print all arguments one by one prints script name; Use shift command in a loop to access each argument and print it correctly loops and prints each argument on new line.

3. Final Answer:

   Use shift command in a loop to access each argument and print it -> Option B

4. Quick Check:

   Shift loops through args one by one [OK]

Hint: Use shift in loop to print each argument separately [OK]

Common Mistakes:

• Using $0 instead of arguments
• Trying to manually count without shift
• Printing all args on one line instead of separate lines