How to Measure Bash Elapsed Time? [Seconds to Milliseconds]

Elapsed time calculation refers to the process of determining the duration that has passed between two specific points in time. Measuring elapsed time is a crucial aspect of Bash scripting that allows users to perform tasks effectively and accurately.

In this article, I’ll show you how to use various techniques to calculate elapsed time in seconds, besides, how to measure elapsed time in nanoseconds and milliseconds in Bash.

What is Elapsed Time in Bash?

Elapsed time is the amount of time that passes from the start to the end of the execution of a script or command. This time interval is used to calculate the time taken to complete a particular task or a series of tasks. It can be measured in seconds, milliseconds, nanoseconds, or other units depending on the precision required. Calculating elapsed time is crucial for a variety of purposes such as script performance monitoring, optimizing resource usage, task scheduling, and so on.

3 Ways to Measure Elapsed Time in Seconds in Bash

To measure elapsed time in seconds, Bash offers various methods. The following section covers 3 different ways to measure elapsed time in seconds in Bash such as using the date command, the built-in variable $SECONDS and the time command with TIMEFORMAT.

1. Using “date” Command

The date command is used to capture timestamps and measure the time difference. You can use the format specifier +%s to print the current time in seconds since the Unix epoch (January 1, 1970, 00:00:00 UTC (Coordinated Universal Time)) before and after an operation and to compute the time difference.

Here’s a Bash script to calculate the elapsed time using date command:

#!/bin/bash

#Capturing the start time
start_time=$(date +%s)

#Performing task
sleep 3

#Capturing the end time
end_time=$(date +%s)

#Calculating elapsed time
elapsed=$((end_time - start_time))

#Displaying elapsed time
echo "Elapsed time is: $elapsed seconds"

The image states the output of the elapsed time which is 3 seconds.

2. Using the Built-in $SECONDS Variable

The $SECONDS is a special built-in variable in Bash that increments by one for each second elapsed since the current shell was invoked or the variable was last reset to zero (0).

When you set the value of the SECONDS variable to 0 before the code block starts, it will reset the count value and start counting the elapsed time from the point of resetting the SECONDS variable.

To calculate the elapsed time using the $SECONDS variable, check out the script below:

#!/bin/bash

#Reset the count of SECONDS variable
SECONDS=0

#Capturing the start time
start_time=$SECONDS

#Performing tasks
sleep 2
sleep 4

#Calculating elapsed time
elapsed_time=$SECONDS

#Displaying elapsed time
echo "Elapsed time using \$SECONDS variable: $elapsed_time seconds"

In the image, you can see that the script displays the elapsed time between resetting $SECONDS and the current moment in that script which is 6 seconds.

3. Employing TIMEFORMAT with “time” Command

The time command calculates the exact execution time of a script or command in Bash. By default, this command provides three time statistics:

1. Elapsed (real) time (%R).
2. User CPU time (%U).
3. System CPU time (%S).

The TIMEFORMAT is a special shell variable that defines the format of the output produced by the time command. When using this variable with the time command, it allows users to customize the output format and display particular time statistics using different format specifiers such as %R, %S, %U etc.

Here’s a Bash script employing the TIMEFORMAT with the time command to get the elapsed time:

#!/bin/bash

#Specifying the format for the output of the 'time' command
TIMEFORMAT='Elapsed time is %R seconds.'

#Measuring elapsed time for the enclosed commands
time {
 echo "Linux"
 sleep 2
 sleep 3
}

From the image, you can see that the elapsed time is 5.016 seconds.

How to Calculate Elapsed Time in Milliseconds?

To calculate elapsed time in milliseconds, use %3N with the date command where %3N specifies the format specifier for milliseconds.

Navigate through the following script to determine elapsed time in milliseconds:

#!/bin/bash

#Capturing start time in milliseconds
start_time=$(date +%s%3N)

#Performing a task
sleep 3

#Capturing end time in milliseconds
end_time=$(date +%s%3N)

#Calculating elapsed time in milliseconds
milli_time=$((end_time - start_time))

#Displaying elapsed time in milliseconds
echo "Elapsed time (milliseconds): $milli_time ms"

This image shows that the elapsed time is 3029 milliseconds (ms).

How to Calculate Elapsed Time in Nanoseconds?

To determine elapsed time in nanoseconds, use the date command with %N that specifies the format specifier for nanoseconds.

Following is a Bash script showing the elapsed time calculation in nanoseconds:

#!/bin/bash

#Capturing start time in nanoseconds
start_time=$(date +%s%N)

#Performing a task
sleep 2

#Capturing end time in nanoseconds
end_time=$(date +%s%N)

#Calculating elapsed time in nanoseconds
nano_time=$((end_time - start_time))

#Displaying elapsed time in nanoseconds
echo "Elapsed time (nanoseconds): $nano_time ns"

The output indicates that the elapsed time is 2008345344 nanoseconds (ns).

Conclusion

So far, you have explored different methods for elapsed time calculation in seconds as well as determining elapsed time in nanoseconds and milliseconds. To sum up, understanding and choosing the appropriate method for measuring elapsed time is crucial for proper performance monitoring in Bash scripts.

People Also Ask

How to check elapsed time in Bash?

To check elapsed time in Bash, you can implement the following methods:

1. Using date command.
2. Using built-in Bash shell variable $SECONDS.
3. Using time command with TIMEFORMAT.

What are some practical use cases for measuring elapsed time in Bash?

Measuring elapsed time in Bash is useful in various schemes when you need to track different tasks’ durations. Let’s see some practical use cases for measuring elapsed time in Bash:

• Monitoring script performance.
• Controlling system processes or commands.
• Resource management.
• Automated task scheduling.
• Timeout handling.
• Optimizing workflow and so on.

What is epoch time, and how is it related to measuring elapsed time in Bash?

Epoch time is a system for representing time as the number of seconds that have elapsed since the Unix epoch (January 1, 1970, 00:00:00 UTC). It is also known as Unix time or POSIX time. This epoch time can be used as a universal reference point when capturing elapsed time in seconds, milliseconds, or even nanoseconds using the date command.

Can elapsed time measurements be affected by external factors?

Yes, elapsed time measurements can be affected by external factors such as high system load, intensive CPU usage, delays in I/O operations, and concurrent processes, etc. that can cause inaccurate time measurements.

Can I convert the measured elapsed time in milliseconds from nanoseconds?

Yes, you can convert the measured elapsed time in milliseconds from nanoseconds. To do so, divide the elapsed time in nanoseconds by 1,000,000. For example:

#!/bin/bash

#Capturing start time in nanoseconds
start_time=$(date +%s%N)

#Performing a task
sleep 3

#Capturing end time in nanoseconds
end_time=$(date +%s%N)

#Calculating elapsed time in nanoseconds
nano_time=$((end_time - start_time))

#Displaying elapsed time in nanoseconds
echo "Elapsed time (nanoseconds): $nano_time ns"

#Converting elapsed time to milliseconds
milli_time=$((nano_time / 1000000))

#Displaying elapsed time in milliseconds
echo "Elapsed time (milliseconds): $milli_time ms"

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