Disk space monitoring script in Bash Scripting - Step-by-Step Execution

Concept Flow - Disk space monitoring script

Start Script

↓

Check disk usage with df

↓

Parse output to get usage %

↓

Compare usage with threshold

↓

Send alert

↓

End Script

The script checks disk usage, compares it to a limit, and sends an alert if usage is too high.

Execution Sample

Bash Scripting

#!/bin/bash
THRESHOLD=80
USAGE=$(df / | tail -1 | awk '{print $5}' | sed 's/%//')
if [ $USAGE -gt $THRESHOLD ]; then
  echo "Disk usage is above threshold!"
fi

This script checks the root disk usage and prints a warning if usage exceeds 80%.

Execution Table

Step	Command/Action	Value/Output	Condition	Branch Taken
1	Set THRESHOLD=80	THRESHOLD=80	N/A	N/A
2	Run df / | tail -1 | awk '{print $5}' | sed 's/%//'	USAGE=85	N/A	N/A
3	Check if USAGE > THRESHOLD	85 > 80	True	Yes branch
4	Print alert message	"Disk usage is above threshold!"	N/A	N/A
5	End script	Script ends	N/A	N/A

💡 Script ends after printing alert because disk usage is above threshold.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
THRESHOLD	unset	80	80	80	80
USAGE	unset	unset	85	85	85

Key Moments - 3 Insights

Why do we remove the % sign from the disk usage output?

The disk usage output includes a % sign (like '85%'), which is not a number. We remove it to compare usage as a number in the condition (see execution_table step 2).

What happens if disk usage is exactly equal to the threshold?

The condition uses 'greater than' (gt), so if usage equals threshold, the alert does NOT trigger (see execution_table step 3).

Why do we use 'tail -1' in the command?

'df' outputs a header line and then data lines. 'tail -1' gets the last line which contains the actual disk usage info (see execution_table step 2).

Visual Quiz - 3 Questions

Look at the execution table, what is the value of USAGE after step 2?

A 80

B 75

C 85

D 90

💡 Hint

Check the 'Value/Output' column in step 2 of the execution_table.

At which step does the script decide to print the alert message?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look for the step where the action is 'Print alert message' in the execution_table.

If the disk usage was 75%, what branch would the script take at step 3?

A No branch (do nothing)

B Yes branch (print alert)

C Error branch

D Loop back to step 2

💡 Hint

Refer to the 'Condition' and 'Branch Taken' columns in step 3 of the execution_table.

Concept Snapshot

Disk space monitoring script syntax:
- Use 'df' to get disk usage.
- Extract usage % and remove '%'.
- Compare usage number with threshold.
- If usage > threshold, send alert.
- Script ends after check.
Simple, effective disk monitoring in bash.

Full Transcript

This script starts by setting a threshold value for disk usage at 80%. It then runs a command to check the current disk usage of the root directory. The output includes a percentage sign, so the script removes it to get a pure number. Next, it compares this number to the threshold. If the usage is greater than 80%, the script prints a warning message. Otherwise, it does nothing and ends. This process helps monitor disk space and alert when usage is too high.