Shifting arguments (shift) in Bash Scripting - Step-by-Step Execution

Concept Flow - Shifting arguments (shift)

Start with all arguments

↓

Use shift command

↓

Remove first argument

↓

Arguments move left

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Check if more arguments

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Process

The shift command removes the first argument and moves all others left, reducing the argument count by one each time.

Execution Sample

Bash Scripting

echo "$1"
shift
echo "$1"
shift
echo "$1"

Prints the first argument, shifts arguments left, then prints the new first argument twice.

Execution Table

Step	Arguments ($@)	Action	Output
1	arg1 arg2 arg3	Print $1	arg1
2	arg2 arg3	shift (remove arg1)
3	arg2 arg3	Print $1	arg2
4	arg3	shift (remove arg2)
5	arg3	Print $1	arg3
6		No more shifts	End

💡 No more arguments to shift after step 5; script ends.

Variable Tracker

Variable	Start	After shift 1	After shift 2	Final
$@	arg1 arg2 arg3	arg2 arg3	arg3
$1	arg1	arg2	arg3

Key Moments - 2 Insights

Why does $1 change after using shift?

Because shift removes the first argument, the second argument moves to $1, as shown in execution_table steps 2 and 3.

What happens if you shift more times than arguments?

Arguments become empty; $1 is empty. The script stops shifting as no arguments remain, as seen after step 5.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of $1 after the first shift?

A arg2

B arg1

C arg3

D empty

💡 Hint

Check the 'After shift 1' column in variable_tracker for $1.

At which step does the script print 'arg3'?

A Step 3

B Step 2

C Step 5

D Step 1

💡 Hint

Look at the Output column in execution_table for 'arg3'.

If the script started with only two arguments, how many times can shift be used before no arguments remain?

A 1

B 2

C 3

D 0

💡 Hint

Each shift removes one argument; see variable_tracker for argument count changes.

Concept Snapshot

shift command in bash removes the first argument ($1).
All other arguments move left by one position.
$# (argument count) decreases by one.
Use shift to process arguments one by one in scripts.

Full Transcript

This visual trace shows how the bash shift command works. Initially, the script has three arguments: arg1, arg2, and arg3. The script prints the first argument ($1), which is arg1. Then it uses shift to remove arg1. After shifting, arg2 becomes the new $1. The script prints $1 again, showing arg2. Another shift removes arg2, making arg3 the new $1. The script prints $1 once more, showing arg3. After this, no more shifts happen because no arguments remain. The variable tracker shows how $@ and $1 change after each shift. Key moments clarify why $1 changes and what happens if you shift too many times. The quiz tests understanding of $1 values after shifts and how many shifts are possible. The snapshot summarizes that shift removes the first argument and moves others left, reducing the argument count.