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Full Discussion: Shell script to generate Fibonacci series using recursion
Top Forums Shell Programming and Scripting Shell script to generate Fibonacci series using recursion Post 302378789 by Scrutinizer on Tuesday 8th of December 2009 08:57:18 PM
Old 12-08-2009
Yes, the recursive approach is not the most efficient way. What is also interesting is the difference between shells. I changed your code yet again a bit so that it would work in any posix shell:

Code:
Fibonacci (){
  case $1 in
    0|1) printf "$1 " ;;
    *)   printf "$(( $(Fibonacci $(($1-2))) + $(Fibonacci $(($1-1))) )) ";;
  esac
}

i=0
while [ $i -lt $1 ]
do
  i=$((i+1))
  Fibonacci $i
done
echo


I tested it with bash zsh, dash and ksh:
Code:
$ time ./testzsh 10
1 1 2 3 5 8 13 21 34 55

real    0m0.837s
user    0m0.180s
sys     0m0.648s
$ time ./testbash 10
1 1 2 3 5 8 13 21 34 55

real    0m0.887s
user    0m0.300s
sys     0m0.580s
$ time ./testdash 10
1 1 2 3 5 8 13 21 34 55

real    0m0.292s
user    0m0.048s
sys     0m0.240s
$ time ./testksh 10
1 1 2 3 5 8 13 21 34 55

real    0m0.092s
user    0m0.088s
sys     0m0.000s

As is my usual experience, ksh is quite a bit faster then other shells.

I also tested a nonrecursive version (timed in ksh):
Code:
$ time ./nonrecurs 10
0 1 1 2 3 5 8 13 21 34 55

real    0m0.013s
user    0m0.016s
sys     0m0.000s

And the difference will become vast once the number goes to 20 and higher.
Last edited by Scrutinizer; 12-08-2009 at 10:23 PM..
 

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LEARN ABOUT SUSE

times

TIMES(1P)						     POSIX Programmer's Manual							 TIMES(1P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       times - write process times

SYNOPSIS

       times

DESCRIPTION

       The times utility shall write the accumulated user and system times for the shell and for all of its  child  processes,	in  the  following
       POSIX locale format:

	      "%dm%fs %dm%fs
%dm%fs %dm%fs
", <shell user minutes>,
		  <shell user seconds>, <shell system minutes>,
		  <shell system seconds>, <children user minutes>,
		  <children user seconds>, <children system minutes>,
		  <children system seconds>

       The  four  pairs  of  times  shall  correspond to the members of the <sys/times.h> tms structure (defined in the Base Definitions volume of
       IEEE Std 1003.1-2001, Chapter 13, Headers) as returned by times(): tms_utime, tms_stime, tms_cutime, and tms_cstime, respectively.

OPTIONS

       None.

OPERANDS

       None.

STDIN

       Not used.

INPUT FILES

       None.

ENVIRONMENT VARIABLES

       None.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

       See the DESCRIPTION.

STDERR

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES

       None.

EXTENDED DESCRIPTION

       None.

EXIT STATUS

       Zero.

CONSEQUENCES OF ERRORS

       Default.

       The following sections are informative.

APPLICATION USAGE

       None.

EXAMPLES

	      $ times
	      0m0.43s 0m1.11s
	      8m44.18s 1m43.23s

RATIONALE

       The times special built-in from the Single UNIX Specification is now required for all conforming shells.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Special Built-In Utilities

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and  the  original  IEEE
       and  The  Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003								 TIMES(1P)
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