Re-print an array in a certain format?

Question

I wish to take 10 random lines of file, which is 100 lines long. First, I randomly generate 10 integers between 1 and 100 (inclusive) with

ind=$(shuf -i 1-100 -n 10 | sort -n)

Then, I wish to use sed to extract out those lines (indicated by ind). So I need to re-print the array ind to generate

<ind(1)>p;<ind(2)>p;...;<ind(10)>p

as in

sed -n '<ind(1)>p;<ind(2)>p;...;<ind(10)>p' ~/orig.txt > ~/short.txt

How may I do this?

cuonglm · Answer 1 · 2015-05-28 03:23:29Z

In your example, ind is a string, not an array. You must use:

ind=($(shuf -i 1-100 -n 10 | sort -n))

to make ind to be array (in shell support array like bash, zsh, ksh).

Simply, you can try:

$ printf '%sp\n' $(shuf -i 1-100 -n 10 | sort -n) > /tmp/short.sed
$ sed -n -f /tmp/short.sed < orig.txt > short.txt

Janis · Answer 2 · 2015-05-27 17:20:50Z

An awk based solution (without need of sorting):

awk 'NR==FNR{a[$1];next} NR in a' <(shuf -i 1-100 -n 10) ~/orig.txt > ~/short.txt

And a pure GNU awk variant (without need of other external processes):

awk '
  BEGIN { srand(); do a[int(100*rand()+1)]; while (length(a)<10) }
  NR in a
' ~/orig.txt > ~/short.txt

2 Answers 2