Progress indicators in Bash Scripting - Step-by-Step Execution

Concept Flow - Progress indicators

Start Task

↓

Initialize Progress

↓

Loop: Update Progress

↓

Display Progress Bar

↓

Check Completion

v +----> Back to Loop↓

End Task

↩v +----> Back to Loop

The script starts a task, initializes progress, then loops updating and displaying the progress bar until the task completes.

Execution Sample

Bash Scripting

total=10
for i in $(seq 1 $total); do
  sleep 0.2
  percent=$((i * 100 / total))
  echo -ne "Progress: $percent%\r"
done
echo

This script shows a simple progress percentage updating in place as a loop runs.

Execution Table

Iteration	i	percent	Action	Output
1	1	10	Calculate percent and display	Progress: 10%
2	2	20	Calculate percent and display	Progress: 20%
3	3	30	Calculate percent and display	Progress: 30%
4	4	40	Calculate percent and display	Progress: 40%
5	5	50	Calculate percent and display	Progress: 50%
6	6	60	Calculate percent and display	Progress: 60%
7	7	70	Calculate percent and display	Progress: 70%
8	8	80	Calculate percent and display	Progress: 80%
9	9	90	Calculate percent and display	Progress: 90%
10	10	100	Calculate percent and display	Progress: 100%
Exit	-	-	Loop ends after i=10	Progress complete

💡 i reaches 10, loop ends, progress reaches 100%

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	After 6	After 7	After 8	After 9	After 10	Final
i	-	1	2	3	4	5	6	7	8	9	10	10
percent	-	10	20	30	40	50	60	70	80	90	100	100

Key Moments - 3 Insights

Why does the progress percentage overwrite the previous output instead of printing new lines?

Because the script uses 'echo -ne' with '\r' (carriage return) to return the cursor to the line start, so the new progress overwrites the old one (see execution_table rows 1-10).

What happens if the sleep command is removed?

The progress updates too fast to see, making the progress bar appear instantly complete (refer to execution_table timing implied by 'sleep 0.2').

Why is there an extra 'echo' after the loop?

To move the cursor to the next line after the progress finishes, so the prompt or next output doesn't overwrite the progress line (after exit row in execution_table).

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'percent' at iteration 5?

A 40

B 60

C 50

D 30

💡 Hint

Check the 'percent' column in the execution_table row for iteration 5.

At which iteration does the loop end according to the execution table?

A 10

B 9

C 11

D 5

💡 Hint

Look for the 'Exit' row and the last iteration number in the execution_table.

If the total variable was changed to 20, how would the 'percent' value at iteration 10 change?

A 20

B 50

C 100

D 10

💡 Hint

Percent is calculated as (i * 100 / total), so at i=10 and total=20, percent = 50.

Concept Snapshot

Progress indicators in bash:
- Use a loop to track progress steps
- Calculate percent: (current_step * 100 / total_steps)
- Use 'echo -ne' with '\r' to overwrite line
- Add 'sleep' to slow updates for visibility
- End with 'echo' to move cursor down

Full Transcript

This visual execution shows how a bash script can display a progress indicator by looping from 1 to total steps. Each iteration calculates the percent complete and prints it on the same line using carriage return '\r'. The sleep command slows the loop so the progress is visible. The loop ends when the counter reaches the total, and a final echo moves the cursor to the next line. Variables 'i' and 'percent' update each iteration, showing progress from 10% to 100%. This method helps users see task progress in the terminal without cluttering output.