Log rotation script in Bash Scripting - Step-by-Step Execution

Concept Flow - Log rotation script

Start script

↓

Check if log file exists

Yes↓

Check log file size > limit?

No→Exit script

Yes↓

Rename current log file to backup

↓

Create new empty log file

↓

Exit script

The script checks if the log file exists and is too big, then renames it and creates a new empty log file.

Execution Sample

Bash Scripting

#!/bin/bash
LOGFILE="app.log"
MAXSIZE=1000
if [ -f "$LOGFILE" ] && [ $(stat -c%s "$LOGFILE") -gt $MAXSIZE ]; then
  mv "$LOGFILE" "$LOGFILE".1
  touch "$LOGFILE"
fi

This script checks if 'app.log' exists and is larger than 1000 bytes, then renames it to 'app.log.1' and creates a new empty 'app.log'.

Execution Table

Step	Check	Condition Result	Action	Output
1	Does 'app.log' exist?	Yes	Proceed to size check
2	Is size of 'app.log' > 1000 bytes?	Yes	Rename 'app.log' to 'app.log.1'
3	Create new empty 'app.log'	N/A	touch 'app.log'
4	End of script	N/A	Exit

💡 Script ends after creating new empty log file.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
LOGFILE	"app.log"	"app.log"	"app.log"	"app.log"	"app.log"
MAXSIZE	1000	1000	1000	1000	1000
app.log file	exists, size > 1000 bytes	exists, size > 1000 bytes	renamed to app.log.1	new empty app.log created	new empty app.log

Key Moments - 3 Insights

Why do we check if the log file exists before checking its size?

Because checking the size of a non-existent file would cause an error. The execution_table row 1 shows we first confirm the file exists.

What happens if the log file size is not greater than the limit?

The script skips renaming and creating a new file and exits immediately, as shown in execution_table row 2 where condition would be No.

Why do we use 'touch' after renaming the log file?

To create a new empty log file so the application can continue logging without errors. This is shown in execution_table row 3.

Visual Quiz - 3 Questions

Look at the execution table, what is the action taken at step 2?

A Rename 'app.log' to 'app.log.1'

B Create new empty 'app.log'

C Exit script

D Check if log file exists

💡 Hint

Refer to execution_table row 2 under 'Action'

At which step does the script create a new empty log file?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at execution_table row 3 under 'Action'

If the log file does not exist, what will the script do?

A Rename the log file

B Exit without any action

C Create a new empty log file

D Throw an error

💡 Hint

Check execution_table row 1 condition result and flow

Concept Snapshot

Log rotation script in bash:
- Check if log file exists
- Check if file size > limit
- If yes, rename old log file
- Create new empty log file
- Exit script
Use 'stat -c%s' for size and 'mv' to rename.

Full Transcript

This bash log rotation script starts by checking if the log file 'app.log' exists. If it does, it checks whether the file size is greater than the maximum allowed size (1000 bytes). If the file is too large, the script renames the current log file to 'app.log.1' to keep it as a backup. Then it creates a new empty 'app.log' file so the application can continue logging without interruption. If the file does not exist or is not too large, the script exits without making changes. This process helps manage log files by preventing them from growing too large and consuming too much disk space.