Overview

In this challenge, I built a Bash script called log_analyzer.sh that automates log analysis and report generation.

The script performs the following tasks:

• Accepts a log file as input

• Validates user input

• Counts errors and failures

• Identifies critical events

• Finds the top 5 most common error messages

• Generates a detailed report

• Archives processed log files

---

log_analyzer.sh

#!/bin/bash

set -euo pipefail

# Check argument
if [ $# -eq 0 ]; then
    echo "Usage: $0 <log_file>"
    exit 1
fi

LOG_FILE=$1

# Validate file
if [ ! -f "$LOG_FILE" ]; then
    echo "Error: File '$LOG_FILE' does not exist."
    exit 1
fi

DATE=$(date +%Y-%m-%d)
REPORT="log_report_${DATE}.txt"

TOTAL_LINES=\((wc -l < "\)LOG_FILE")

ERROR_COUNT=\((grep -Ei "ERROR|Failed" "\)LOG_FILE" | wc -l)

CRITICAL_EVENTS=\((grep -n "CRITICAL" "\)LOG_FILE" || true)

TOP_ERRORS=\((grep "ERROR" "\)LOG_FILE" \
| sed 's/^.*ERROR //' \
| sort \
| uniq -c \
| sort -rn \
| head -5)

{
echo "========================================="
echo "       DAILY LOG ANALYSIS REPORT"
echo "========================================="
echo ""
echo "Date of Analysis : $(date)"
echo "Log File         : $LOG_FILE"
echo "Total Lines      : $TOTAL_LINES"
echo "Total Errors     : $ERROR_COUNT"

echo ""
echo "----- Top 5 Error Messages -----"
echo "$TOP_ERRORS"

echo ""
echo "----- Critical Events -----"
echo "$CRITICAL_EVENTS"

} > "$REPORT"

echo ""
echo "================================="
echo "Analysis Complete"
echo "================================="
echo "Total Errors Found : $ERROR_COUNT"
echo "Report Generated   : $REPORT"

# Optional Archive Feature
mkdir -p archive

mv "$LOG_FILE" archive/

echo "Archived Log File To: archive/"

---

Sample Log File

2026-06-06 10:10:11 INFO Application Started
2026-06-06 10:11:05 ERROR Connection timed out
2026-06-06 10:11:15 ERROR Connection timed out
2026-06-06 10:11:20 ERROR File not found
2026-06-06 10:12:01 CRITICAL Database connection lost
2026-06-06 10:13:50 Failed Login Attempt
2026-06-06 10:15:25 ERROR Permission denied
2026-06-06 10:18:12 CRITICAL Disk space below threshold
2026-06-06 10:19:01 ERROR Connection timed out

---

Running the Script

Make executable:

chmod +x log_analyzer.sh

Execute:

./log_analyzer.sh sample_log.log

---

Console Output

=================================
Analysis Complete
=================================
Total Errors Found : 5
Report Generated   : log_report_2026-06-06.txt
Archived Log File To: archive/

---

Generated Report

File:

log_report_2026-06-06.txt

Content:

=========================================
       DAILY LOG ANALYSIS REPORT
=========================================

Date of Analysis : Fri Jun 06 12:30:15 UTC 2026
Log File         : sample_log.log
Total Lines      : 9
Total Errors     : 5

----- Top 5 Error Messages -----

3 Connection timed out
1 Permission denied
1 File not found

----- Critical Events -----

5:2026-06-06 10:12:01 CRITICAL Database connection lost

8:2026-06-06 10:18:12 CRITICAL Disk space below threshold

---

Commands and Tools Used

Command	Purpose
grep	Search keywords
grep -n	Display line numbers
grep -c	Count occurrences
wc -l	Count total lines
sort	Sort output
uniq -c	Count duplicate entries
head -5	Display top 5 results
sed	Extract error messages
mv	Move processed logs
mkdir -p	Create archive directory

---

Task Mapping

Task 1 – Input Validation

if [ $# -eq 0 ]; then

Checks whether a log file was provided.

if [ ! -f "$LOG_FILE" ]; then

Checks if the file exists.

---

Task 2 – Error Count

grep -Ei "ERROR|Failed" "$LOG_FILE"

Counts all ERROR and Failed entries.

---

Task 3 – Critical Events

grep -n "CRITICAL" "$LOG_FILE"

Displays critical events along with line numbers.

---

Task 4 – Top Error Messages

grep "ERROR" "$LOG_FILE"

Extracts errors.

sort | uniq -c | sort -rn

Finds the most common error messages.

---

Task 5 – Summary Report

Creates:

log_report_<date>.txt

containing:

• Analysis date

• Log file name

• Total lines

• Total errors

• Top 5 errors

• Critical events

---

Task 6 – Archive Processed Logs

mkdir -p archive
mv "$LOG_FILE" archive/

Moves processed logs into the archive directory.

---

What I Learned

1. Log Analysis Can Be Automated

Instead of manually checking logs, Bash scripts can quickly generate meaningful summaries.

2. Linux Text Processing Tools Are Powerful

Commands such as:

grep
awk
sed
sort
uniq

can analyze thousands of log entries in seconds.

3. Automation Improves Operations

Automated log analysis helps identify issues faster and reduces manual effort.

---

Conclusion

This challenge demonstrated how Bash scripting can be used to automate log monitoring and reporting tasks. By combining tools like grep, sed, sort, and uniq, I created a reusable log analyzer that identifies errors, highlights critical events, generates reports, and archives processed logs automatically.

Day 20 completed successfully.