time - macOS

Overview

The time command executes a specified command or script and reports the time it takes to complete. It provides detailed performance metrics that can be valuable for optimizing code and identifying performance bottlenecks.

Syntax

time [-p] [-v] [-o file] [-a] [-l] [-f format] command [args...]

Options/Flags

  • -p: Print both real and CPU time in the format “real user sys “.
  • -v: Verbose mode. Print command output along with timing information.
  • -o file: Write timing information to the specified file instead of stdout.
  • -a: Append timing information to the specified file instead of overwriting it.
  • -l: Print timing information in a long format, displaying additional details.
  • -f format: Specify a custom output format string. See man time for details.

Examples

  • Execute a command and print the real and CPU time:
time ls -l /usr/bin
  • Execute a script and print the timing information to a file:
time ./my_script.sh -o timing.log
  • Use verbose mode to display command output and timing information:
time -v python my_program.py

Common Issues

  • Command not found: Ensure that the specified command is installed and available in the system path.
  • Timing information not printed: Check if the correct options are specified. By default, only the real time is printed. Use -p for both real and CPU time.
  • Incorrect output format: Verify the specified custom format string using man time. The default format is “real %e user %U sys %S”.

Integration

  • Combine with other commands to measure the performance of specific tasks:
time cp -R /src/ /dst/
  • Create scripts to automate performance testing and generate reports:
#!/bin/sh

for i in {1..10}; do
    echo "Iteration $i"
    time ./my_program.py
done
  • top: Monitor system performance and resource usage.
  • perf: Perform low-level performance profiling and optimization.
  • resourcelimits: Set resource limits for processes, including CPU time.