Shifting arguments (shift) in Bash Scripting - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to shift the first argument out of the list.

Bash Scripting

#!/bin/bash

# Shift the first argument
shift [1]

echo "$1"

Drag options to blanks, or click blank then click option'

A1

B2

C0

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'shift 0' does not shift any arguments.

Using a negative number like 'shift -1' causes an error.

Using 'shift 1' removes the first argument, so $1 becomes the second argument.

2fill in blank

medium

Complete the code to shift two arguments at once.

Bash Scripting

#!/bin/bash

# Shift two arguments
shift [1]

echo "$1"

Drag options to blanks, or click blank then click option'

A0

B1

C3

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'shift 1' only removes one argument.

Using 'shift 0' does not remove any arguments.

Using 'shift 2' removes the first two arguments, so $1 becomes the third argument.

3fill in blank

hard

Fix the error in the code to correctly shift one argument.

Bash Scripting

#!/bin/bash

# Incorrect shift usage
shift [1]

echo "$1"

Drag options to blanks, or click blank then click option'

A-1

Bone

C1

Dfirst

Attempts:

3 left

💡 Hint

Common Mistakes

Using words like 'one' or 'first' instead of numbers.

Using negative numbers like '-1'.

The 'shift' command requires a positive integer number, so '1' is correct.

4fill in blank

hard

Fill both blanks to shift arguments and print the new first argument.

Bash Scripting

#!/bin/bash

# Shift arguments
shift [1]
echo [2]

Drag options to blanks, or click blank then click option'

A2

B"$1"

C"$2"

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Printing "$2" after shifting 2 arguments prints the wrong argument.

Using shift 1 but printing "$2" causes confusion.

Shifting by 2 removes first two arguments, so $1 is the new first argument to print.

5fill in blank

hard

Fill all three blanks to shift arguments and print the second argument after shifting.

Bash Scripting

#!/bin/bash

# Shift arguments
shift [1]
echo [2]
echo [3]

Drag options to blanks, or click blank then click option'

A1

B"$1"

C"$2"

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using shift 1 but printing $2 and $3 instead of $1 and $2.

Printing $1 twice instead of $1 and $2.

Shifting by 2 removes first two arguments, so $1 and $2 are the new first and second arguments.

Practice

1. What does the shift command do in a bash script?

easy

A. It moves all command-line arguments one position to the left, dropping the first argument.

B. It duplicates the first argument to the end of the list.

C. It reverses the order of all command-line arguments.

D. It prints all command-line arguments without changes.

Solution

1. Step 1: Understand the role of shift

   The shift command removes the first argument and shifts all others left.

2. Step 2: Effect on arguments

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

3. Final Answer:

   It moves all command-line arguments one position to the left, dropping the first argument. -> Option A

4. Quick Check:

   shift drops first argument [OK]

Hint: Remember: shift drops first argument and moves others left [OK]

Common Mistakes:

• Thinking shift duplicates arguments
• Assuming shift reverses arguments
• Believing shift prints arguments unchanged

2. Which of the following is the correct syntax to shift two arguments in a bash script?

easy

A. shift --2

B. shift -2

C. shift 2

D. shift 1 1

Solution

1. Step 1: Recall shift syntax

   The correct syntax to shift by a number is shift N, where N is a positive integer.

2. Step 2: Identify valid option

   shift 2 shifts by two arguments; negative or multiple numbers are invalid.

3. Final Answer:

   shift 2 -> Option C

4. Quick Check:

   Use shift N with positive N [OK]

Hint: Use 'shift N' with positive number N to shift multiple args [OK]

Common Mistakes:

• Using negative numbers with shift
• Trying to pass multiple numbers
• Using invalid flags like --2

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

echo $1
shift
echo $1

medium

A. apple\napple

B. banana\ncherry

C. banana\napple

D. apple\nbanana

Solution

1. Step 1: Check initial $1 value

   Before shift, $1 is the first argument: 'apple'.

2. Step 2: Apply shift and check new $1

   After shift, $1 becomes the second argument: 'banana'.

3. Final Answer:

   apple\nbanana -> Option D

4. Quick Check:

   First echo prints first arg, second echo prints second arg after shift [OK]

Hint: First echo shows $1, shift moves args left, second echo shows new $1 [OK]

Common Mistakes:

• Assuming shift does not change $1
• Confusing argument positions after shift
• Expecting output to be 'banana\ncherry'

4. Identify the error in this script snippet:

shift 3
echo $1

Assuming the script is run with only two arguments.

medium

A. Error: shift 3 tries to shift more arguments than exist, causing an error.

B. No error; it prints the first argument unchanged.

C. Error: shift requires a negative number to work.

D. No error; it prints the third argument.

Solution

1. Step 1: Check number of arguments

   The script has only two arguments but tries to shift by three.

2. Step 2: Understand shift behavior on excess shift

   Shifting more than available arguments causes an error or empties all arguments.

3. Final Answer:

   Error: shift 3 tries to shift more arguments than exist, causing an error. -> Option A

4. Quick Check:

   Shifting beyond argument count causes error [OK]

Hint: Don't shift more than available arguments to avoid errors [OK]

Common Mistakes:

• Assuming shift works with negative numbers
• Ignoring argument count before shifting
• Expecting shift to print unchanged arguments

5. You want to process all command-line arguments one by one in a bash script using shift. Which script snippet correctly does this?

hard

A. for arg in "$@"; do shift; echo "$arg"; done

B. while [ "$#" -gt 0 ]; do echo "$1"; shift; done

C. shift; while [ "$#" -gt 0 ]; do echo "$1"; done

D. while [ "$#" -ge 1 ]; do echo "$2"; shift 2; done

Solution

1. Step 1: Understand argument count and shifting

   Use while [ "$#" -gt 0 ] to loop while arguments remain.

2. Step 2: Print first argument and shift each iteration

   Inside loop, print $1 then shift to move to next argument.

3. Final Answer:

   while [ "$#" -gt 0 ]; do echo "$1"; shift; done -> Option B

4. Quick Check:

   Loop with shift processes all args one by one [OK]

Hint: Use while loop with $# and shift to process args one by one [OK]

Common Mistakes:

• Using for loop with shift inside causing skipped args
• Not updating argument count in loop condition
• Shifting by 2 causing missed arguments