How to Time How Long a Command or Script Takes

It is no doubt that time is the most important resource we have. As a sys admin, you will constantly monitor your script and command time usage more times not.

Especially when configuring multiple devices, determining how long a script or command takes to complete can allow you to determine when is the right to perform maintenance, etc.

Get your cup of coffee ready and let's jump in.

Linux time Command

The time command in Linux and other Unix systems provides us with the ability to monitor how long a command takes.

The time command is built-in all major shells and available in almost all Linux devices. The command follows a syntax as shown below:

time [-al] [-h | -p] [-o file] utility [argument ...]

The command accepts the following options:

     -a      If the -o flag is used, append to the specified file rather than overwriting it.
             Otherwise, this option has no effect.

     -h      Print times in a human friendly format.  Times are printed in minutes, hours, etc. as
             appropriate.

     -l      The contents of the rusage structure are printed as well.

     -o file
             Write the output to file instead of stderr.  If file exists and the -a flag is not
             specified, the file will be overwritten.

     -p      Makes time output POSIX.2 compliant (each time is printed on its own line).

Example 1 - time command without parameters

If we run the time command without any arguments, the command will time details when the command run. These includes statistics such as the elapsed real time between invocation and termination, elaspsed user CPU time, system CPU time, etc.

Example:

time

Output:

shell  0.02s user 0.05s system 0% cpu 6:18.79 total
children  0.61s user 0.32s system 0% cpu 6:18.79 total

Example 2 - Time the ls Command

The example below shows how to use the time command to determine how long it takes to list files and directories in the /var/log directory.

time ls -la /var/log

The command should show the file listing followed by the elapsed duration stats. A sample output is as shown:

ls -la /var/log  0.00s user 0.01s system 65% cpu 0.019 total

Keep in mind that the elapsed time is calculated in CPU seconds and not human seconds.

Conclusion

In this tutorial, we explored how to time how long a command or a script takes to finish execution using the time command. You can check the man pages with the command man time to discover further.

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