Zsh: measure command durations with the time command, TIMEFMT, and REPORTTIME

time is a POSIX utility for timing commands. Most shells build it in, and Zsh’s version has a lot more to offer than the one in Bash. Put time before a command to time it. For example, to time a Python script: $ time python example.py python example.py 1.33s user 1.73s system 74% cpu 4.114 total When the command finishes, Zsh prints a single line to standard error, which contains: python example.py: the command, or “job”, that was timed. 1.33s user: user CPU time, the time the CPU spent running the program’s own code. 1.73s system: system CPU time, the time the CPU spent in the kernel on the program’s behalf. 74% cpu: the amount of CPU used in the duration, calculated as (user + system) / elapsed. 4.114 total: the elapsed time, also known as “wall clock time”, from start to finish. This one-line format differs from Bash’s time, which prints three lines, labelled real, user, and sys. But the numbers have the same meanings. The CPU percentage is a useful clue for what a program is…

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