Bash Script to Rotate Log Files Automatically

Use a Bash script that renames the current log file with a number suffix and deletes the oldest, like mv logfile.log logfile.log.1; rm -f logfile.log.5 to rotate logs up to 5 versions.

Examples

Inputlogfile.log exists with content

Outputlogfile.log renamed to logfile.log.1; logfile.log is empty for new logs

Inputlogfile.log.1 to logfile.log.4 exist, logfile.log updated

Outputlogfile.log.4 deleted; logfile.log.3 renamed to logfile.log.4; ...; logfile.log renamed to logfile.log.1

InputNo logfile.log present

OutputNo action taken; script exits without error

How to Think About It

To rotate log files, the script moves older logs up one number, deletes the oldest if needed, and renames the current log to start fresh. This keeps logs manageable and prevents disk space issues.

Algorithm

1

Check if the main log file exists; if not, exit.

2

Delete the oldest rotated log if it exists (e.g., logfile.log.5).

3

Shift existing rotated logs up by one number (e.g., logfile.log.4 to logfile.log.5).

4

Rename the current log file to logfile.log.1 to archive it.

5

Create a new empty logfile.log for fresh logging.

Code

bash

#!/bin/bash
LOGFILE="logfile.log"
MAX=5

if [ ! -f "$LOGFILE" ]; then
  echo "No log file to rotate."
  exit 0
fi

# Remove oldest log
if [ -f "$LOGFILE.$MAX" ]; then
  rm -f "$LOGFILE.$MAX"
fi

# Shift logs
for ((i=MAX-1; i>=1; i--)); do
  if [ -f "$LOGFILE.$i" ]; then
    mv "$LOGFILE.$i" "$LOGFILE.$((i+1))"
  fi
done

# Rotate current log
mv "$LOGFILE" "$LOGFILE.1"

# Create new empty log
> "$LOGFILE"
echo "Log rotation complete."

Output

Log rotation complete.

Dry Run

Let's trace rotating logfile.log when logfile.log.1 to logfile.log.4 exist and logfile.log has new data.

1

Check if logfile.log exists

logfile.log exists, continue

2

Delete oldest log if exists

logfile.log.5 does not exist, no deletion

3

Shift logs up by one

logfile.log.4 -> logfile.log.5 logfile.log.3 -> logfile.log.4 logfile.log.2 -> logfile.log.3 logfile.log.1 -> logfile.log.2

4

Rename current log

logfile.log -> logfile.log.1

5

Create new empty logfile.log

logfile.log is now empty

Operation
Check logfile.log exists
Remove logfile.log.5 if exists
Move logfile.log.4 to logfile.log.5
Move logfile.log.3 to logfile.log.4
Move logfile.log.2 to logfile.log.3
Move logfile.log.1 to logfile.log.2
Rename logfile.log to logfile.log.1
Create empty logfile.log

Why This Works

Step 1: Check for log file

The script first checks if logfile.log exists to avoid errors when rotating.

Step 2: Delete oldest log

It removes the oldest rotated log (e.g., logfile.log.5) to keep only a fixed number of backups.

Step 3: Shift logs

Older logs are renamed to the next number to make room for the new rotated log.

Step 4: Rotate current log

The current log is renamed to logfile.log.1, archiving it.

Step 5: Create new log

A new empty logfile.log is created so logging can continue fresh.

Alternative Approaches

Using logrotate tool

bash

sudo apt-get install logrotate
# Create /etc/logrotate.d/mylog with config:
# /path/to/logfile.log {
#   rotate 5
#   daily
#   missingok
#   notifempty
#   copytruncate
# }
# Then run: logrotate /etc/logrotate.d/mylog

logrotate is a standard Linux tool for log rotation with many options but requires config files and root access.

Compress old logs during rotation

bash

#!/bin/bash
LOGFILE="logfile.log"
MAX=5
if [ ! -f "$LOGFILE" ]; then exit 0; fi
if [ -f "$LOGFILE.$MAX.gz" ]; then rm -f "$LOGFILE.$MAX.gz"; fi
for ((i=MAX-1; i>=1; i--)); do
  if [ -f "$LOGFILE.$i.gz" ]; then mv "$LOGFILE.$i.gz" "$LOGFILE.$((i+1)).gz"; fi
  if [ -f "$LOGFILE.$i" ]; then gzip "$LOGFILE.$i"; fi
done
mv "$LOGFILE" "$LOGFILE.1"
gzip "$LOGFILE.1"
> "$LOGFILE"
echo "Compressed log rotation complete."

Compressing saves disk space but adds CPU overhead and complexity.

Complexity: O(n) time, O(1) space

Time Complexity

The script loops through existing rotated logs once, so time grows linearly with the number of rotations.

Space Complexity

No extra memory is used beyond renaming files; operations are in-place on disk.

Which Approach is Fastest?

The simple Bash script is fast for small numbers of rotations; using logrotate adds overhead but offers more features.

Approach	Time	Space	Best For
Bash script rotation	O(n)	O(1)	Simple setups with few logs
logrotate tool	O(n)	O(1)	Complex rotation policies and automation
Compression during rotation	O(n)	O(1)	Saving disk space with CPU cost