Bash for loop - naming after n (which is user's input)

Question

I am looping over the commands with for i in {1..n} loop and want output files to have n extension.

For example:

  for i in {1..2}
  do cat FILE > ${i}_output
  done

However n is user's input:

  echo 'Please enter n'
  read number
  for i in {1.."$number"}
  do 
    commands > ${i}_output
  done

Loop rolls over n times - this works fine, but my output looks like this {1..n}_output.

How can I name my files in such loop?

Edit

Also tried this

  for i in {1.."$number"} 
  do
    k=`echo ${n} | tr -d '}' | cut -d "." -f 3`
    commands > ${k}_output
  done

But it's not working.

http://stackoverflow.com/questions/169511/how-do-i-iterate-over-a-range-of-numbers-in-bash — KBart, Feb 14 '13 at 08:20

johnsyweb · Accepted Answer · 2013-02-14T08:39:03.323

9

echo 'Please enter n'
read number
for ((i = 1; i <= number; i++))
do 
    commands > ${i}_output
done

Note that the $ is not required ahead of number or i in the for-loop header but double-parentheses are required.

edited Feb 14 '13 at 08:39

answered Feb 14 '13 at 08:21

johnsyweb

P.P · Answer 2 · 2013-02-14T08:40:16.930

3

The range parameter in for loop works only with constant values. So replace {1..$num} with a value like: {1..10}.

OR

Change the for loop to:

  for((i=1;i<=number;i++))

edited Feb 14 '13 at 08:40

answered Feb 14 '13 at 08:21

P.P

1

`i <= number` or you'll miss the last element. And you don't need the `$` there, either (see my answer). – johnsyweb Feb 14 '13 at 08:31
@Johnsyweb Fixed it. But $ doesn't hurt either :) – P.P Feb 14 '13 at 08:41

score 0 · Answer 3 · answered Feb 14 '13 at 08:24

0

You can use a simple for loop ( similar to the ones found in langaues like C, C++ etc):

echo 'Please enter n'
read number
for (( i=1; i <= $number; i++ ))
do
  commands > ${i}_output
done

answered Feb 14 '13 at 08:24

vaisakh

`i <= number`. No `$`. – johnsyweb Feb 14 '13 at 08:36
@Johnsyweb, I tried that out. Seems both are working. :) – vaisakh Feb 14 '13 at 08:38
Great :-) Every day's a school-day. – johnsyweb Feb 14 '13 at 08:40
Right..I learned something new too. Thanks! :) – vaisakh Feb 14 '13 at 08:53

Christian Kiewiet · Answer 4 · 2013-02-14T13:32:35.857

-1

Try using seq (1) instead. As in for i in $(seq 1 $number).

edited Feb 14 '13 at 13:32

answered Feb 14 '13 at 08:16

Christian Kiewiet

`seq` involves the execution of an external command that may slow things down, but I'm not sure that warrants a downvote. – johnsyweb Feb 14 '13 at 08:37

4 Answers4