How do you time how long a command took to run? [duplicate]

use time:

$ time somecommand --with=somearguments 

time will execute the rest of the command line (in this example somecommand --with=somearguments ) and when the command is done it will print the elapsed time.

example output:

$ time somecommand --with=somearguments ... ... (output of somecommand) ... real 0m5,020s user 0m0,010s sys 0m0,010s 

the information that you typically want is real. in this example the command took about 5 seconds. for more information about the other numbers see here: https://stackoverflow.com/questions/556405/what-do-real-user-and-sys-mean-in-the-output-of-time1

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the example output above is from the bash builtin. time is a builtin command in most shells. there is also the system time. it has a different output format but otherwise behaves mostly the same as the shell builtin.

for more information about the difference of a shell builtin and a system command see here: What is the difference between a builtin command and one that is not?

to use the system command you do it like this:

$ /usr/bin/time somecommand --what=islove 

or

$ env time somecommand --baby=donthurtme 

there are more but that is outside the scope of this question and answer.

for more info how to invoke system command see here: Use system command instead of Bash builtin without specifying the full path

example output using system time:

$ env time somecommand --donthurtme=nomore ... ... (output of somecommand) ... 0.00user 0.01system 0:06.02elapsed 0%CPU (0avgtext+0avgdata 3656maxresident)k 0inputs+0outputs (0major+1089minor)pagefaults 0swaps 

the information that you typically want is elapsed. in this example the command took about 6 seconds. for the meaning of the other numbers i have not found a good explanation in the internet. you have to read the man page: http://man7.org/linux/man-pages/man1/time.1.html

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the system time is more flexible in output. here some demonstration

you can change the output of the system time. for example use -p to get output similar to the shell builtin time:

$ /usr/bin/time -p somecommand --what=isyourname ... real 0:06.02 user 0.00 sys 0.01 

or use -f to write your own format:

$ /usr/bin/time -f %E somecommand --what=isyourquest ... 0:06.02 

%E is the "elapsed" part. the part you are usually most interested in.

for completeness: you can also change the bash builtin time output format by changing this variable: TIMEFORMAT. more info: https://www.gnu.org/software/bash/manual/html_node/Bash-Variables.html#index-TIMEFORMAT

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how to redirect or capture the output

for demonstration observe command hellostdoutstderr:

#!/bin/sh sleep 0.5 echo "hello out" echo "hello err" >&2 

example invocations:

 $ ./hellostdoutstderr hello out hello err 

capture stdout and stderr separately

$ ./hellostdoutstderr >stdoutfile 2>stderrfile $ cat stdoutfile hello out $ cat stderrfile hello err 

the system time prints to stderr so it is captured with the stderr redirect

$ /usr/bin/time ./hellostdoutstderr >stdoutfile 2>stderrfile $ cat stdoutfile hello out $ cat stderrfile hello err 0.00user 0.00system 0:00.50elapsed 1%CPU (0avgtext+0avgdata 3672maxresident)k 0inputs+16outputs (0major+311minor)pagefaults 0swaps 

you can tell the system time to print to a separate file

$ /usr/bin/time -o timeoutfile ./hellostdoutstderr >stdoutfile 2>stderrfile $ cat stdoutfile hello out $ cat stderrfile hello err $ cat timeoutfile 0.00user 0.00system 0:00.50elapsed 1%CPU (0avgtext+0avgdata 3676maxresident)k 0inputs+16outputs (0major+309minor)pagefaults 0swaps 

note that the bash builtin time always prints to the terminal even if stdout and stderr is redirected. this is possible because it is a builtin and can do whatever it likes (in the shell)

$ time ./hellostdoutstderr >stdoutfile 2>stderrfile real 0m0,511s user 0m0,005s sys 0m0,006s 

in this example stdout and stderr are both redirected to file. but bash builtin time still prints to terminal.

with tricks it is still possible to capture the output of the bash builtin. but why fight bash if it is easier to use system command. if you are so inclined here is more info: https://www.cyberciti.biz/faq/unix-linux-time-command-examples-usage-syntax/

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to time more complex commands you have severals options

if you just want to time two command one after the other

$ time { command1 ; command2 ; } 

also works with pipe

$ time { command1 | command2 ; } 

for more complex stuff

$ time sh -c ' complex command chain ' 

but mind the quoting and other shenanigans. better put the commands in a script and time the script:

$ time ./script.sh 

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TL;DR: add time before your command. if you want to measure time inside a script use /usr/bin/time.