[Linux] Bash watch uso: Execute a command periodically

Overview

The watch command in Bash is a useful utility that allows you to execute a specified command at regular intervals. This is particularly helpful for monitoring changes in the output of commands, such as system resource usage or file changes.

Usage

The basic syntax of the watch command is as follows:

watch [options] [arguments]

Common Options

• -n, --interval <seconds>: Specify the interval in seconds between command executions. The default is 2 seconds.
• -d, --differences: Highlight the differences between successive outputs.
• -t, --no-title: Disable the display of the header showing the command being executed and the interval.
• -x, --exec: Execute the command with the specified arguments.

Common Examples

Example 1: Monitor Disk Usage

To monitor the disk usage of the root directory every 5 seconds, you can use:

watch -n 5 df -h /

Example 2: Check Running Processes

To see the list of running processes and update it every 2 seconds:

watch ps aux

Example 3: Monitor a Log File

To monitor the last 10 lines of a log file and see updates:

watch tail -n 10 /var/log/syslog

Example 4: Highlight Changes

To highlight changes in the output of a command, such as checking the contents of a directory:

watch -d ls -l /path/to/directory

Tips

• Use the -n option to adjust the refresh rate according to your needs; a shorter interval can provide real-time monitoring.
• Combine watch with commands that generate dynamic output to effectively track changes.
• Use the -t option if you want a cleaner output without the header, which can be useful for scripts or logging.