Linux / Unix: time Command Examples

I am new Linux and Unix systems user. How do I display the time of the execution of a command/script on Linux or Unix-like operating systems using shell prompt?

You need to use the time command to display the elapsed time during the execution of a command or script. This page explains time command in Linux and Unix-like system with most common examples.

1. real time
2. user time
3. sys time

Purpose

Run command/programs or script and summarize system resource usage on your screen.

Syntax

The basic syntax is as follows:
$ time command
$ time command arg1 arg2 ... argN
$ time [options] command arg1 arg2 ... argN

Is my time command shell built-in or external command?

The time command is also built into the BASH/KSH/CSH/TCSH with a different syntax. Let us use the type command or command command to verify location:
$ type -a time
$ command -V time
Here is what I see:

time is a shell keyword
time is /usr/bin/time
time is /bin/time

Calling external time command using a full path

Users of the bash or ksh shell need to use an explicit path in order to run the external time command and not the shell builtin variant. To run the time command while in the shells, type:
$ /usr/bin/time -p command
$ /bin/time -p command arg1 arg2

time command examples

To measure the time required to run a program called date, enter:
$ time date
To use external time command give full path to time binary:
$ /usr/bin/time -p date

How do I redirect time command output to a file?

The syntax is as follows to save a record of the time command information in a file called output.time.txt, run:

time date 2> output.time.txt
/usr/bin/time -p date 2> output.time.txt

If above command failed, try the following to save a record of the time command information in a file:

( time date ) 2> output.time.txt
## OR ##
{ time date ; } 2> output.time.txt

Use the cat command to display output on screen:
$ cat output.time.txt

A note about GNU/Linux time command

GNU/Linux user can use the following syntax to write the resource use statistics to file instead of to the standard error stream:
$ /usr/bin/time -o output.time.txt -p date
$ cat output.time.txt
Pass the -a option to append the resource use information to the output file instead of overwriting it. This option is only useful with the -o option:
$ /usr/bin/time -a -o output.time.txt -p sleep 2
$ cat output.time.txt

Using time command on my Linux system

Use FORMAT as the format string that controls the output of time

Using time command on Linux or Unix with formatting

In this example, show just the user, system, and total time using format option:
$ /usr/bin/time -f "%E real,%U user,%S sys" sleep 2
$ /usr/bin/time -f "%E real,%U user,%S sys" /path/to/script
Sample outputs:

0:02.00 real,0.00 user,0.00 sys

See percentage of CPU used by your command:
$ /usr/bin/time -f "CPU Percentage: %P" command
$ /usr/bin/time -f "CPU Percentage: %P" grep vivek /etc/passwd
$ /usr/bin/time -f "CPU Percentage: %P" find /etc/ -type f -iname "a*.conf"
CPU Percentage: 76%

Understanding TIMEFORMAT used by bash’s buitin time

The value of TIMEFORMAT parameter is used as a format string specifying how the timing information for pipelines prefixed with the time reserved word should be displayed. The % character introduces an escape sequence that is expanded to a time value or other information. The escape sequences and their meanings are as follows; the braces denote optional portions.

How to use bash’s builtin time command in Linux / Unix

The syntax is almost same:
$ time command
$ time ls
$ TIMEFORMAT="%P" time ls
$ TIMEFORMAT="%U" time sleep 3
$ TIMEFORMAT="%S" time sleep 3
$ TIMEFORMAT="%R" time sleep 2

Summing up

You learned about the time command that reports the time consumed by the pipeline’s execution. It will summarize system resource usage on the screen. The syntax of time might change on your local Unix or Linux distro. Hence, to get help for builtin time command, type the following help command:
$ help time
# or read shell man page
$ man bash
For external time (/bin/time or /usr/bin/time) command, run the following man command:
$ man time

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Vivek Gite is an expert IT Consultant with over 25 years of experience, specializing in Linux and open source solutions. He writes about Linux, macOS, Unix, IT, programming, infosec, and open source. Follow his work via RSS feed or email newsletter.