anyone know of a faster / shorter / better way of doing the following?

for x in *; do echo $RANDOM $x; done | sort -n | head -n1 | cut -d " "
-f 2

thanks.

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usr.bin.python@gmail.com wrote:
> anyone know of a faster / shorter / better way of doing the following?
>
> for x in *; do echo $RANDOM $x; done | sort -n | head -n1 | cut -d " "
> -f 2
>
> thanks.
>

Using only shell builtins...

set - * ; eval printf "%s\\\\n" \$$(( $RANDOM % $# ))


Janis

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Janis Papanagnou wrote:
> usr.bin.python@gmail.com wrote:
> 
>
> Using only shell builtins...
>
> set - * ; eval printf "%s\\\\n" \$$(( $RANDOM % $# ))

I meant...

set - * ; eval printf "%s\\\\n" \$$(( $RANDOM % $# + 1 ))

Janis

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> >> anyone know of a faster / shorter / better way of doing the following? 
>    set - * ; eval printf "%s\\\\n" \$$(( $RANDOM % $# + 1 ))
> Janis


cool... mind explaining to me how it works?

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Janis Papanagnou wrote:
> Janis Papanagnou wrote: 
> I meant:    set - * ; eval printf "%s\\\\n" \$$(( $RANDOM % $# + 1 ))

No you didn't! ;) You meant:

set - * ; eval printf '%s\\n' \${(( RANDOM%$#+1 ))}

If there are 17 command line arguments (say) you don't
want to evaluation $17 -- that's ${1}7 in most shells.

And especially for ksh(1): doing variable substitution
within arithmetric substitution is (almost) always slower,
and problematic in some situations as well.

Also: I think using the squotes in the printf expression
is a little cleaner.

=Brian

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On 2006-01-26, usr.bin.python@gmail.com wrote:
> anyone know of a faster / shorter / better way of doing the following?
>
> for x in *; do echo $RANDOM $x; done | sort -n | head -n1 | cut -d " "
> -f 2

set -- *
eval "printf '%s\n' \"\${$(( $RANDOM % $# + 1 ))}\""


--
Chris F.A. Johnson, author   |    <http://cfaj.freeshell.org>
Shell Scripting Recipes:     |  My code in this post, if any,
A Problem-Solution Approach  |          is released under the
2005, Apress                 |     GNU General Public Licence

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In article <1138244809.084677.96090@g47g2000cwa.googlegroups.com>,
usr.bin.python@gmail.com wrote:
 
>
>
> cool... mind explaining to me how it works?

Don't you think you'll learn more by trying to figure it out yourself?
Everything you need to know should be in the shell man page.

--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***

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usr.bin.python@gmail.com wrote:
> anyone know of a faster / shorter / better way of doing the following?
>
> for x in *; do echo $RANDOM $x; done | sort -n | head -n1 | cut -d " "
> -f 2

perl -le'$x = 1; rand($x++) < 1 && ($file = $_) while <*>; print $file'


John
--
use Perl;
program
fulfillment

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On 25 Jan 2006 18:11:45 -0800, usr.bin.python@gmail.com wrote:
> anyone know of a faster / shorter / better way of doing the following?
>
> for x in *; do echo $RANDOM $x; done | sort -n | head -n1 | cut -d " "
> -f 2
[...]

(yours doesn't work properly with filenames containing spaces,
tabs, newlines or backslashes)

For shells with $RANDOM (that's not POSIX)

set ./*
shift "$(($RANDOM % $#))"

the file is in $1

The probability distribution for all the possible filenames will
not necessarily be even.


POSIXly:

awk '
BEGIN {
srand()
print ARGV[int(rand() * (ARGC - 1)) + 1]
exit
}' ./*



--
Stephane

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usr.bin.python@gmail.com wrote: 
>
> cool... mind explaining to me how it works?

The building blocks are...

set - *    The shell expands all files and assigns their names to
$1, $2, ..., $<N>
$#         The number of arguments <N>
$(( $RANDOM % $# + 1 ))
Make your arithmetic, a random number between 1 and <N>
eval ... \${ $expression }
Since the arithmetic needs to be expanded first to get
some index, you need to escape the first $ to not be
considered by the shell, and in a second "indirection"
step, which is done by eval, to get the actual argument.

Somewhat simplified the expansion steps are...

"Step 0":  eval echo \${$(( $RANDOM % $# + 1 ))}
"Step 1":  eval echo \${$(( 789     % 22 + 1 ))}
"Step 2":  eval echo \${20}
"Step 3":       echo  ${20}
"Step 4":       echo fileNr20


Janis

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