The Linux Time Command: An Overview

The Linux time command is a utility that is used to measure the execution time of a command or program. It can be useful for testing the performance of different commands or programs, or for identifying bottlenecks in the execution process.

The time command is built into the Linux shell, and can be used by running time followed by the command or program that you want to measure. For example, to measure the execution time of the ls command, you could run:

time ls

When the time command is run, it will display the execution time of the command or program in the following format:

real    time   
user    time   
sys     time   

The real time is the total elapsed time that the command or program took to execute, including any time spent waiting for resources or input/output operations. The user time is the amount of CPU time that was spent executing the command or program in user mode. The sys time is the amount of CPU time that was spent executing the command or program in kernel mode.

The time command has a number of options that can be used to customize its behavior. For example, you can use the -p option to display the output in a portable format, or the -f option to specify a custom format for the output. You can also use the --append option to append the execution time to a file, rather than displaying it on the command line.

In addition to measuring the execution time of a command or program, the time command can also be used to measure the resources that are consumed by the command or program. For example, you can use the --verbose option to display the maximum resident set size (RSS) of the command or program, or the --output option to specify a file to which the output should be written.

Linux Time Command Examples

Display the output in a portable format: To display the output of the time command in a portable format, you can use the -p option. This can be useful if you want to parse the output of the time command using a script or program. For example:

time -p ls

This will display the execution time of the ls command in the following format:

real    time   
user    time   
sys     time   

Specify a custom format for the output: To specify a custom format for the output of the time command, you can use the -f option. This can be useful if you want to customize the output of the time command to include only specific information. For example:

time -f "Elapsed time: %E" ls

This will display the elapsed time (%E) of the ls command in the following format:

Elapsed time: time   

Append the execution time to a file: To append the execution time of a command or program to a file, rather than displaying it on the command line, you can use the --append option. For example:

time --append -o

The time command is a useful tool for measuring the execution time and resource consumption of different commands or programs in Linux. It can be used to troubleshoot performance issues, or to optimize the performance of different commands or programs.