bash how to measure execution time

The command "time" report a execution time information

time sleep 1

Output:
real 0m1.001s
user 0m0.000s
sys 0m0.001s

Description:

• Real - time from start to finish
• User - the amount of CPU time spent in use-mode. It is actual CPU time used in executing the process
• Sys - the amount of CPU time spent in kernel

You can measure execution time by subtraction start date and end date:

start=`date +%s`
commands...
end=`date +%s`
echo Execution time was `expr $end - $start` seconds.

If you need to have more accurate measure:

start=`date +%s%N`
commands...
end=`date +%s%N`
echo Execution time was `expr $end - $start` nanoseconds.

Adding %N to date +%s causes nanosecond accuracy.

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