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1

I have an executable that does the following: 1. outputs the string BEGIN 2. wait for some random time 3. outputs the string END

I want to do the following with a python/bash/perl script on MacOS:

  1. execute the program mentioned before from command line
  2. record the time between the BEGIN message and the END message outputted by the program

how do I do this cleanly?

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Do you have access to the source code of this binary ? It would be simpler (and more precise) to display a time stamp with BEGIN/END messages directly inside the program. –  Antonin Portelli Dec 15 '10 at 23:43
3  
What @Antonin Portelli says is correct. Watching the output of one process from another using a pipe will give inaccurate timing results because of system overhead and buffering -- so unless the external program timestamps its own output, some other form of low-overhead interprocess communication is needed. –  martineau Dec 16 '10 at 1:11

4 Answers 4

up vote 1 down vote accepted

The easiest (best?) way to do this in bash is to just call date and have it output it's time in seconds. The timer.sh script will call your executable (randbegend.sh for my testing purposes) and then look for the BEGIN and END lines to trigger the call to date. Once your executable quits, timer.sh will then calculate and display the time delta in seconds.

timer.sh

#!/bin/bash

while read line; do
  if [[ "$line" == "BEGIN" ]]; then
    t1=$(date "+%s")
    echo t1=$t1
  elif [[ "$line" == "END" ]]; then
    t2=$(date "+%s")
    echo t2=$t2
  fi
done < <(./randbegend.sh) # Change this to call your executable

echo "delta = $((t2 - t1)) seconds"

randbegend.sh

#!/bin/bash

sleep $((RANDOM % 5))
echo BEGIN
sleep $((RANDOM % 10))
echo END

Output

$ ./timer.sh
t1=1292451820
t2=1292451825
delta = 5 seconds

$ ./timer.sh
t1=1292451886
t2=1292451889
delta = 3 seconds

$ ./timer.sh
t1=1292451896
t2=1292451903
delta = 7 seconds
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up vote 1 down vote

If you want only whole-second granularity, you can do the following "one-liner" in perl:

( echo BEGIN ; sleep 3s ; echo END ) | \
    perl -ne 'print $_; if (/BEGIN/) { $begin_time = time(); } if (/END/) { $t = time()-$begin_time; print "time was : $t seconds" }'

Produces:

BEGIN
[ 3 second delay ]
END
time was : 3 seconds

You'd stick your command line execution of your program where I have ( echo BEGIN ; sleep 3s ; echo END ).

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up vote 0 down vote

In Python:

You can use the datetime module to make a note of the current timestamp, before and after the execution of the external program, and then subtract the two to get the execution time.

You can execute external programs using the subprocess module.

So the code would look something like:

import datetime, subprocess

ts1 = datetime.datetime.now()
subprocess.Popen('/path/to/external/program')
ts2 = datetime.datetime.now()
print ts2-ts1
share|improve this answer
    
This doesn't address the possibility that his executable does a few things before the output of BEGIN and a few things after the output of END. –  SiegeX Dec 15 '10 at 23:37
    
Well, that is true, but he did not mention that is a possibility. –  infrared Dec 15 '10 at 23:41
    
This isn't a solution if the BEGIN/END messages do not appear exactly at the start/end of the runtime, and anyway it is simpler to use the time command –  Antonin Portelli Dec 15 '10 at 23:41
    
subprocess.Popen doesn't wait for the command/external-program to finish, so the time difference computed it largely independent of how long it might take that finish its execution (especially since it doesn't watch for the BEGIN/END outputs). –  martineau Dec 16 '10 at 0:57
up vote 0 down vote

You can do it simply with GAWK :

exec | gawk '{if ($1 == "BEGIN") {t1 = systime()} else if ($1 == "END") {t2 = systime()}} END{print t2-t1" sec"}'

where exec is your executable. This is good only if you don't need a precision more accurate than one second.

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