I needed to test out some work just completed, and to do so, I needed to run some files against a process. Problem is, there are 1000 files to choose from, and I only want to test a handful.
But which handful? Ideally, it would be random.
So here's my quick shell hack to give me 15 random files from a given directory:
ls | while read x; do echo "`expr $RANDOM % 1000`:$x"; done \
| sort -n| sed 's/[0-9]*://' | head -15
This works by:
- Generating a list of every file in the directory
- Reading in each file into the variable x
- I prepend a random number (thanks to the magic $RANDOM variable in bash
- I then sort that listing numerically - which means sorting based on the random number
- I then strip off the random number
- I show only 15 items from the stream
Of course, this isn't efficient - but it doesn't need to be. Heck, it took longer to write up the blog post describing it, then it did to actually write the code.
I so love Unix. And I'm running this under cygwin on a Windows box. See, there's no excuse for not using Unix.
creative script, and a nice photo of you and your girlfriend by the way. I used in my script a trick I read somewhere else: the -R option of GNU sort does a random sort. But that option is not in the POSIX specification of sort on unix.org
ReplyDeleteit works. thanks!
ReplyDeletesed definitely works in this instance, but perhaps using cut would be more elegant?
ReplyDeleteeg:
cut -d':' -f2-
Just my two cents; in the end, as long as it works, it's all good.
Thanks for this; it's definitely helping!
I always forget about cut -- that's a good point.
ReplyDelete-Ben
That's pretty elegant. Thanks
ReplyDeleteJust found out about this (does same thing):
ReplyDeletels |sort -R | head -n5
When using in something like a 'find' command, it helps to use 'expr' as such:
ReplyDeletefind /home/ -name "*.mp3" -exec \
sh -c 'echo `expr $RANDOM` {}' ";" \
| sort -g\
| awk '{print $2}'
ls | sort -R | head -1
ReplyDeletels | sort -R | head -15
ReplyDeleteHow would one then have the script open the output? Thanks for your help.
ReplyDeleteEvan
you can do what you like by using a while read e.g.
Deletels | sort -R | head -15 | while read file
do
cat $file
done
Great. This is works like a gem - Is it possible to also copy the file name shown on $x variable to a different folder? if so how?
ReplyDeleteyes:
Deletels | sort -R | head -15 | while read file
do
cp $file /tmp/
done
Just replace /tmp/ with which ever folder you want to copy to.
Just do it more efficiently by omitting `expr $RANDOM % 1000` which gives no advantage:
ReplyDeletels | while read x; do echo "$RANDOM:$x"; done | sort -n|cut -d':' -f2| head -15
time results with just "$RANDOM:$x"
real 0m0.04s
user 0m0.04s
sys 0m0.05s
time results with "`expr $RANDOM % 1000`:$x":
real 0m1.85s
user 0m0.50s
sys 0m1.32s
What about the easy way?
ReplyDeletefind -type f | shuf -n1