Bash Script to Check Memory Usage Easily

Use the command free -h inside a Bash script to check memory usage in a human-readable format, for example: #!/bin/bash free -h.

Examples

InputRun script on a system with 8GB RAM

Output total used free shared buff/cache available Mem: 7.7Gi 2.1Gi 3.5Gi 200Mi 2.1Gi 5.0Gi Swap: 2.0Gi 0B 2.0Gi

InputRun script on a system with 16GB RAM and some usage

Output total used free shared buff/cache available Mem: 15.6Gi 6.2Gi 5.0Gi 300Mi 4.4Gi 8.5Gi Swap: 4.0Gi 512Mi 3.5Gi

InputRun script on a system with very low memory

Output total used free shared buff/cache available Mem: 1.9Gi 1.7Gi 100Mi 50Mi 100Mi 200Mi Swap: 1.0Gi 900Mi 100Mi

How to Think About It

To check memory usage in Bash, you can use the free command which shows total, used, and free memory. Adding the -h option makes the output easy to read by showing sizes in KB, MB, or GB.

Algorithm

1

Run the <code>free -h</code> command to get memory usage details.

2

Capture the output to display or process further if needed.

3

Print the output to the user.

Code

bash

#!/bin/bash
# Script to check memory usage
free -h

Output

              total        used        free      shared  buff/cache   available
Mem:           7.7Gi       2.1Gi       3.5Gi       200Mi       2.1Gi       5.0Gi
Swap:          2.0Gi          0B       2.0Gi

Dry Run

Let's trace running the script on a system with 8GB RAM and some usage.

1

Run free -h command

Command outputs memory stats in human-readable form.

2

Display output

Shows total, used, free memory and swap info.

total	used	free	shared	buff/cache	available
7.7Gi	2.1Gi	3.5Gi	200Mi	2.1Gi	5.0Gi

Why This Works

Step 1: Use of free command

The free command reports memory usage including RAM and swap.

Step 2: Human-readable output

The -h option converts bytes into KB, MB, or GB for easy reading.

Step 3: Simple script

Running free -h inside a script quickly shows memory stats without extra setup.

Alternative Approaches

Using /proc/meminfo

bash

#!/bin/bash
awk '/MemTotal|MemFree|Buffers|Cached/ {print}' /proc/meminfo

Shows detailed memory info but less user-friendly output.

Using vmstat command

bash

#!/bin/bash
vmstat -s | grep 'memory'

Provides memory stats in a different format, useful for performance monitoring.

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

Time Complexity

The script runs a single system command that executes in constant time regardless of memory size.

Space Complexity

No extra memory is used beyond storing the command output temporarily.

Which Approach is Fastest?

Using free -h is fastest and simplest; parsing /proc/meminfo or vmstat adds complexity without speed benefits.

Approach	Time	Space	Best For
free -h	O(1)	O(1)	Quick, readable memory check
/proc/meminfo parsing	O(1)	O(1)	Detailed memory info
vmstat	O(1)	O(1)	Performance monitoring