Ubuntu CMD Time - Shell-Bash

Introduction

As a programmer, working with the command line interface (CLI) is an essential part of our job. One of the most common tasks we perform on the CLI is measuring the time taken to execute a command or a script.

In this article, we will learn how to use the time command on Ubuntu to measure the execution time of a shell script or a command. We will also cover some advanced features of the time command, such as redirecting the output to a file and disabling the shell's built-in time command.

Basic Usage

The time command is a built-in utility on Ubuntu, which is used to measure the duration of a program's execution. In its most basic form, you can run the time command followed by a command or a script that you want to measure:

time command

For example, let's measure the time it takes to execute the ls command, which lists the contents of a directory:

time ls

This will output the following information:

real    0m0.004s
user    0m0.004s
sys     0m0.000s

The output consists of three lines:

• real: This is the actual time taken by the program to execute, including any overhead time, such as setting up the environment, loading libraries, or writing output to the console.
• user: This is the amount of CPU time used by the program, executing in user mode, without considering any system calls or kernel operations.
• sys: This is the amount of CPU time used by the program, executing in kernel mode, performing system calls or other privileged operations.

Advanced Usage

Outputting to a File

The time command can also output the results to a file, instead of displaying them on the console. This is useful when you need to measure the execution time of a command or a script, but you do not want to clutter the console output.

To redirect the output of the time command to a file, you can use the standard output redirection operator >:

time command > output.log

For example, to measure the execution time of a script test.sh and save the output to a file output.log, you can use:

time ./test.sh > output.log

Disabling the Shell's Built-in Time Command

By default, Ubuntu's shell (Bash) has a built-in time command that performs a similar function to the /usr/bin/time command we have been using until now. However, the shell's time command outputs timing information in a different format and does not provide as much detail as the time command we have been using.

To disable the shell's built-in time command and use the /usr/bin/time command instead, you can prefix your command or script with the full path to the time command, like so:

/usr/bin/time command

For example, to disable the shell's built-in time command and measure the execution time of the ls command, you can use:

/usr/bin/time ls

This will output timing information in the same format as before:

real    0m0.004s
user    0m0.004s
sys     0m0.000s

Conclusion

In this article, we learned how to use the time command on Ubuntu to measure the execution time of a command or a script. We also covered some advanced features of the time command, such as redirecting the output to a file and disabling the shell's built-in time command.

By mastering the time command, you can optimize your programs and scripts, and identify performance bottlenecks.