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Top Forums Shell Programming and Scripting Comparing two numbers with decimal point Post 302369497 by ghostdog74 on Sunday 8th of November 2009 10:20:55 PM
Old 11-08-2009
Quote:
Originally Posted by cfajohnson
[indent]
When dealing with a string, an external program is many, many times slower than using shell internals.

Code:
$ x=123.456
$ time echo "${x%.*}"
123

real    0m0.000s
user    0m0.000s
sys     0m0.000s
$ time echo "$x" | awk -F. '{print $1}'
123

real    0m0.045s
user    0m0.002s
sys     0m0.001s

not many times slower.... you are using echo to pipe to awk, an extra pipe process increase the time.
Code:
# time awk -v v="$x" -F"." 'BEGIN{print $1}'

real    0m0.003s
user    0m0.001s
sys     0m0.001s

# time echo "$x" | awk -F. '{print $1}'
123

real    0m0.004s
user    0m0.001s
sys     0m0.003s

its just 0.003s. not that big a difference. Besides that, for an apple to apple comparison, its not even accurate. The above awk statement already had the 2nd field stored in memory and can be used anytime, whereas the shell one does not.


Quote:
I have an 80-line shell function, fpmul, which multiplies floating point numbers.
who would want to write and maintain an 80 lines code instead of one line ? your timing and my timing may differ since we may have different processors. Here's my timing:
Code:
$ time awk 'BEGIN { print 12.34 * 56.78 * 90.12; exit }'
63143.9

real    0m0.003s
user    0m0.000s
sys     0m0.002s

same with bc
Code:
$ time echo "12.34 * 56.78 * 90.12" |bc
63143.47

real    0m0.003s
user    0m0.000s
sys     0m0.005s

In the end, it doesn't really matter a big deal. The only big deal is, you write 80 lines of code to perform only a mere 0.003s difference with a one liner.

Quote:
On the contrary, complicated programs can be written in the shell that perform faster than those using another language.
that's not true . Complicated programs should not be written with shell, period. They should be written with languages like Python, or Perl with modules. There are simply many things that shell can't do very well.

Quote:
There are times when an external program is better, especially dealing with large files.
a tool that can process small and large files efficiently is still better than one that only works well on small files

Quote:
Since most people will have some familiarity with the shell, it is faster to learn to use it well than to learn a new programming language.
not really true. the shell's syntax is not exactly friendly to use. A programming language for example Python has easy to read syntax, and with that respect, reading and deciphering code is "faster", thereby easier to learn than shell.


Nowadays its not about speed of program execution, but speed of script development and easier code maintenance.
 

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