On how to select the right tool for a given task Post: 302249572

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Top Forums Shell Programming and Scripting On how to select the right tool for a given task Post 302249572 by neked on Tuesday 21st of October 2008 03:42:23 PM

10-21-2008

Registered User

Quote:

Originally Posted by neked

3) Even if you were a parameter substitution guru, and you used meaningful variable names and comments to make clearer what your parameter substitution tricks do, then future maintainers of the code might not be the same. This bit me a couple of days ago: I had to spend 20 minutes debugging a bash script riddled with those parameter substitution scripts. I estimate I would've spent closer to 5 minutes if the code was written using more obvious external tools (sed, basename, awk). This is about 15 minutes of human time wasted in order to save less than a few milliseconds of CPU time. Especially since the whole script runs only once a night, and does not exceed 0.030 seconds runtime on my modest 7 years old computer.

I've just substituted all occurrences of parameter substitutions with equivalent sed and basename commands in the script I refer to above, the execution time went up from an average of 0.030 seconds to 0.061 seconds. That means parameter substitution use shaved an average of 0.03 seconds per run. Considering that I've had to spend roughly 15 more minutes understanding the code to debug it, this means the code has to run 15*60/0.03 times to pay off the extra time I invested to debug it. That's 30,000 times. Considering that it runs once a night, this means we'll have to wait more than 80 years!

Even after 80 years, those 0.020 seconds shaved off CPU time per night are not as worthy to me as 15 minutes of my time which I could've spent aternative activity redacted

Last edited by Perderabo; 10-21-2008 at 05:49 PM.. Reason: clean up language

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LEARN ABOUT NETBSD

time

TIME(3) 						   BSD Library Functions Manual 						   TIME(3)

NAME

     time -- get time of day

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <time.h>

     time_t
     time(time_t *tloc);

DESCRIPTION

     The time() function returns the value of time in seconds since 0 hours, 0 minutes, 0 seconds, January 1, 1970, Coordinated Universal Time.

     A copy of the time value may be saved to the area indicated by the pointer tloc.  If tloc is a NULL pointer, no value is stored.

     Upon successful completion, time() returns the value of time.  Otherwise a value of ((time_t) -1) is returned and the global variable errno
     is set to indicate the error.

ERRORS

     No errors are defined.

SEE ALSO

     gettimeofday(2), ctime(3)

STANDARDS

     The time() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1'').

HISTORY

     A time() function appeared in Version 2 AT&T UNIX.  It returned a 32-bit value measuring sixtieths of a second, leading to rollover every
     2.26 years.  In Version 6 AT&T UNIX, the precision of time() was changed to seconds, allowing 135.6 years between rollovers.

     In NetBSD 6.0 the time_t type was changed to be 64 bits wide, including on 32-bit machines, making rollover a concern for the far distant
     future only.  Note however that any code making the incorrect assumption that time_t is the same as long will fail on 32-bit machines in
     2038.

BSD
								 November 5, 2011							       BSD