Displaying number of columns and items in columns using a for loop

Question

I'm writing a BASH script that asks a user for the number of columns and the number of items to put in the columns. The script will then put the numbers in the columns using for loops.

# Number of columns
cols=$1

# Number of items
num=$2

# Iterator variable
count=1

# Number of rows
rows=$(( ($num + ($cols - 1)) / $cols ))

for x in $(seq 1 1 $rows)
do
  for y in $(seq 1 1 $cols)
  do
    echo -ne "$count\t"

    (( count++ ))
  done

  echo ""
done

For example, if I enter 6 columns with 28 items this is what the output should look like.

1   2   3   4   5   6
7   8   9   10  11  12
13  14  15  16  17  18
19  20  21  22  23  24
25  26  27  28

However, this is the output I get with the current code.

1   2   3   4   5   6
7   8   9   10  11  12
13  14  15  16  17  18
19  20  21  22  23  24
25  26  27  28  29  30

Thanks in advance for everyone's help!

Kusalananda · Accepted Answer · 2021-05-07 06:00:11Z

You never have to calculate the number of rows needed. You just need to make sure that you insert newlines after every $cols number.

Using seq and awk:

$ num=28
$ cols=6
$ seq "$num" | awk -v cols="$cols" '{ printf "%-4d", $1 } NR % cols == 0 { printf "\n" } END { printf "\n" }'
1   2   3   4   5   6
7   8   9   10  11  12
13  14  15  16  17  18
19  20  21  22  23  24
25  26  27  28

This prints each digit read from seq as a left-justified decimal number, allowing four characters of width for each, with no trailing newline. And it then outputs a newline after whenever a row of numbers have been printed, and at the very end.

Using the rs tool:

$ num=28
$ cols=6
$ seq "$num" | rs 0 "$cols"
1   2   3   4   5   6
7   8   9   10  11  12
13  14  15  16  17  18
19  20  21  22  23  24
25  26  27  28

If you need to do this using a shell loop in e.g. bash:

$ num=28
$ cols=6
$ for ((i=1; i<=num; ++i)); do printf '%-4d' "$i"; (( i%cols == 0 )) && echo; done; echo
1   2   3   4   5   6
7   8   9   10  11  12
13  14  15  16  17  18
19  20  21  22  23  24
25  26  27  28

This mimics the awk code at the start.

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