I want to execute something in a linux shell under a few different conditions, and be able to output the execution time of each execution.
I know I could write a perl or python script that would do this, but is there a way I can do it in the shell? (which happens to be bash)
Use the built-in time keyword:
$ help time
time: time [-p] PIPELINE
Execute PIPELINE and print a summary of the real time, user CPU time,
and system CPU time spent executing PIPELINE when it terminates.
The return status is the return status of PIPELINE. The `-p' option
prints the timing summary in a slightly different format. This uses
the value of the TIMEFORMAT variable as the output format.
Example:
$ time sleep 2
real 0m2.009s user 0m0.000s sys 0m0.004s
time -p i=x; while read line; do x=x; done < /path/to/file.txt? It immediatly returns 0.00 unless I don't put anything before the while loop.. what gives?
time can time an entire pipeline as-is (by virtue of being a Bash keyword), you need to use a group command ({ ...; ...; }) to time multiple commands: time -p { i=x; while read line; do x=x; done < /path/to/file.txt; }
type -a timeYou can get much more detailed information than the bash built-in time (i.e time(1), which Robert Gamble mentions). Normally this is /usr/bin/time.
Editor's note:
To ensure that you're invoking the external utility time rather than your shell's time keyword, invoke it as /usr/bin/time.
time is a POSIX-mandated utility, but the only option it is required to support is -p.
Specific platforms implement specific, nonstandard extensions: -v works with GNU's time utility, as demonstrated below (the question is tagged linux); the BSD/macOS implementation uses -l to produce similar output - see man 1 time.
Example of verbose output:
$ /usr/bin/time -v sleep 1
Command being timed: "sleep 1"
User time (seconds): 0.00
System time (seconds): 0.00
Percent of CPU this job got: 1%
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:01.05
Average shared text size (kbytes): 0
Average unshared data size (kbytes): 0
Average stack size (kbytes): 0
Average total size (kbytes): 0
Maximum resident set size (kbytes): 0
Average resident set size (kbytes): 0
Major (requiring I/O) page faults: 0
Minor (reclaiming a frame) page faults: 210
Voluntary context switches: 2
Involuntary context switches: 1
Swaps: 0
File system inputs: 0
File system outputs: 0
Socket messages sent: 0
Socket messages received: 0
Signals delivered: 0
Page size (bytes): 4096
Exit status: 0
#!/bin/bash
START=$(date +%s)
# do something
# start your script work here
ls -R /etc > /tmp/x
rm -f /tmp/x
# your logic ends here
END=$(date +%s)
DIFF=$(( $END - $START ))
echo "It took $DIFF seconds"
For a line-by-line delta measurement, try gnomon.
$ npm install -g gnomon
$ <your command> | gnomon --medium=1.0 --high=4.0 --ignore-blank --real-time=100
A command line utility, a bit like moreutils's ts, to prepend timestamp information to the standard output of another command. Useful for long-running processes where you'd like a historical record of what's taking so long.
You can also use the --high and/or --medium options to specify a length threshold in seconds, over which gnomon will highlight the timestamp in red or yellow. And you can do a few other things, too.
Should you want more precision, use %N with date (and use bc for the diff, because $(()) only handles integers).
Here's how to do it:
start=$(date +%s.%N)
# do some stuff here
dur=$(echo "$(date +%s.%N) - $start" | bc)
printf "Execution time: %.6f seconds" $dur
Example:
start=$(date +%s.%N); \
sleep 0.1s; \
dur=$(echo "$(date +%s.%N) - $start" | bc); \
printf "Execution time: %.6f seconds\n" $dur
Result:
Execution time: 0.104623 seconds
If you intend to use the times later to compute with, learn how to use the -f option of /usr/bin/time to output code that saves times. Here's some code I used recently to get and sort the execution times of a whole classful of students' programs:
fmt="run { date = '$(date)', user = '$who', test = '$test', host = '$(hostname)', times = { user = %U, system = %S, elapsed = %e } }"
/usr/bin/time -f "$fmt" -o $timefile command args...
I later concatenated all the $timefile files and pipe the output into a Lua interpreter. You can do the same with Python or bash or whatever your favorite syntax is. I love this technique.
/usr/bin/time is necessary because although which time will tell you otherwise, if you simply run time, it will run your shell's version of time which does not accept any arguments.
env time :-)If you only need precision to the second, you can use the builtin $SECONDS variable, which counts the number of seconds that the shell has been running.
while true; do
start=$SECONDS
some_long_running_command
duration=$(( SECONDS - start ))
echo "This run took $duration seconds"
if some_condition; then break; fi
done
... SECONDS=0; some_long_running_command; echo "This run took $SECONDS seconds" ..., cf. man bashYou can use time and subshell ():
time (
for (( i=1; i<10000; i++ )); do
echo 1 >/dev/null
done
)
Or in same shell {}:
time {
for (( i=1; i<10000; i++ )); do
echo 1 >/dev/null
done
}
( & ) (new context, subshell), and other with { & } (same shell, same context)The way is
$ > g++ -lpthread perform.c -o per
$ > time ./per
output is >>
real 0m0.014s
user 0m0.010s
sys 0m0.002s
-lphtread or -o tags. Just need to use the time command, which the accepted answer explains better.
one possibly simple method ( that may not meet different users needs ) is the use of shell PROMPT.it is a simple solution that can be useful in some cases. You can use the bash prompting feature as in the example below:
export PS1='[\t \u@\h]\$'
The above command will result in changing the shell prompt to :
[HH:MM:SS username@hostname]$
Each time you run a command (or hit enter) returning back to the shell prompt, the prompt will display current time.
notes:
1) beware that if you waited for sometime before you type your next command, then this time need to be considered, i.e the time displayed in the shell prompt is the timestamp when the shell prompt was displayed, not when you enter command. some users choose to hit Enter key to get a new prompt with a new timestamp before they are ready for the next command.
2) There are other available options and modifiers that can be used to change the bash prompt, refer to ( man bash ) for more details.
perf stat Linux CLI utility
This tool is overkill for just getting time. But it can do so much more for you to help profile and fix slowness that it is worth knowing about. Ubuntu 22.04 setup:
sudo apt install linux-tools-common linux-tools-generic
echo -1 | sudo tee /proc/sys/kernel/perf_event_paranoid
Usage:
perf stat <mycmd>
Sample run with stress-ng:
perf stat stress-ng --cpu 1 --cpu-method matrixprod -t 5
Sample output:
Performance counter stats for 'stress-ng --cpu 1 --cpu-method matrixprod -t 5':
5,005.46 msec task-clock # 0.999 CPUs utilized
88 context-switches # 17.581 /sec
1 cpu-migrations # 0.200 /sec
1,188 page-faults # 237.341 /sec
18,847,667,167 cycles # 3.765 GHz
26,544,261,897 instructions # 1.41 insn per cycle
3,239,655,001 branches # 647.225 M/sec
25,393,369 branch-misses # 0.78% of all branches
5.012218939 seconds time elapsed
4.998051000 seconds user
0.009122000 seconds sys
perf can also do a bunch more advanced things, e.g. here I show how to use it to profile code: How do I profile C++ code running on Linux?
Tickslike the windows case?