Log rotation script in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this log rotation snippet?

Consider this bash snippet that rotates a log file by renaming it with a timestamp. What will be the output if the current date is 2024-06-15 and the log file exists?

Bash Scripting

LOGFILE="app.log"
BACKUP="app.log.$(date +%F)"
if [ -f "$LOGFILE" ]; then
  mv "$LOGFILE" "$BACKUP"
  echo "Rotated $LOGFILE to $BACKUP"
else
  echo "No log file to rotate"
fi

A No log file to rotate

B Rotated app.log to app.log.2024-06-15

C Rotated app.log to app.log.$(date +%F)

D Error: date command not found

💡 Hint

Check how the date command is used inside the variable BACKUP.

The script checks if the log file exists. If yes, it renames it by appending the current date in YYYY-MM-DD format. The echo confirms the rename with the expanded date.

🔧 Debug

intermediate

Why does this log rotation script fail to rotate logs?

This script is intended to rotate a log file by compressing the old log and creating a new empty log. Why does it fail to compress the old log?

Bash Scripting

LOGFILE="server.log"
if [ -f "$LOGFILE" ]; then
  gzip $LOGFILE
  > $LOGFILE
  echo "Log rotated and compressed"
else
  echo "No log to rotate"
fi

A The if condition uses -f which does not detect regular files.

B The > $LOGFILE line is invalid syntax and causes an error.

C The gzip command removes the original file, so > $LOGFILE creates a new empty file with the same name, but the script expects the compressed file to exist.

D The script does not check if gzip is installed, so it fails silently.

💡 Hint

Think about what gzip does to the original file after compression.

gzip compresses the file and deletes the original. The script then creates a new empty file with the original name. This works as intended, but if the script expects the original file to remain uncompressed, it will fail.

🚀 Application

advanced

Which script correctly rotates logs keeping only last 5 backups?

You want a bash script that renames the current log file by appending the date, compresses it, and deletes backups older than 5 days. Which script does this correctly?

A

LOGFILE="app.log"
BACKUP="app.log.$(date +%F)"
if [ -f "$LOGFILE" ]; then
  mv "$LOGFILE" "$BACKUP"
  gzip "$BACKUP"
  find . -name 'app.log.*.gz' -mtime +5 -exec rm -f {} \;
  touch "$LOGFILE"
fi

B

LOGFILE="app.log"
BACKUP="app.log.$(date +%F)"
if [ -f "$LOGFILE" ]; then
  mv "$LOGFILE" "$BACKUP"
  gzip "$BACKUP"
  find . -name 'app.log.*.gz' -mtime +5 -delete
  touch "$LOGFILE"
fi

C

LOGFILE="app.log"
BACKUP="app.log.$(date +%F)"
if [ -f "$LOGFILE" ]; then
  cp "$LOGFILE" "$BACKUP"
  gzip "$LOGFILE"
  find . -name 'app.log.*.gz' -mtime +5 -exec rm {} \;
  > "$LOGFILE"
fi

D

LOGFILE="app.log"
BACKUP="app.log.$(date +%F)"
if [ -f "$LOGFILE" ]; then
  mv "$LOGFILE" "$BACKUP"
  gzip "$LOGFILE"
  find . -name 'app.log.*.gz' -mtime +5 -delete
  touch "$LOGFILE"
fi

💡 Hint

Check which file is compressed and how old backups are deleted.

Option A moves the log file to a dated backup, compresses that backup, deletes compressed backups older than 5 days, and creates a new empty log file. It uses rm -f with find -exec which is correct and safe.

📝 Syntax

advanced

Which option has a syntax error in this log rotation script?

Identify the option that contains a syntax error preventing the script from running.

Bash Scripting

LOGFILE="access.log"
BACKUP="access.log.$(date +%F)"
if [ -f "$LOGFILE" ]; then
  mv "$LOGFILE" "$BACKUP"
  gzip "$BACKUP"
  touch "$LOGFILE"
fi

A

f [ -f "$LOGFILE" ]; then
  mv "$LOGFILE" "$BACKUP"
  gzip "$BACKUP"
  touch "$LOGFILE"
fi

B

if [ -f "$LOGFILE" ]; then
  mv "$LOGFILE" "$BACKUP"
  gzip "$BACKUP"
  touch "$LOGFILE"
fi

C

if
"ELIFGOL$" hcuot  
"PUKCAB$" pizg  
"PUKCAB$" "ELIFGOL$" vm  
neht ;] "ELIFGOL$" f- [ fi

D

if [ -f "$LOGFILE" ] then
  mv "$LOGFILE" "$BACKUP"
  gzip "$BACKUP"
  touch "$LOGFILE"
fi

💡 Hint

Check the syntax of the if statement carefully.

Option D is missing the semicolon or newline before 'then' in the if statement, causing a syntax error.

🧠 Conceptual

expert

What is the main reason to compress rotated logs in automation?

In automated log rotation scripts, why is compressing old log files important?

A To reduce disk space usage by storing logs in a smaller size

B To make logs easier to read by humans

C To prevent logs from being deleted accidentally

D To speed up the creation of new log files

💡 Hint

Think about storage and resource management.

Compressing old logs saves disk space by reducing file size, which is critical for systems generating large logs over time.