How to display numbers in reverse order using seq(1)?

I have iterate over numbers in various order. I am able to display them in increasing order, even with steps like:

$ seq --separator="," 1 10
1,2,3,4,5,6,7,8,9,10
$ seq --separator="," 1 2 10
1,3,5,7,9

I am also able to display them in reverse order, neither continuous nor step wise.

$ seq --separator="," 10 1   
$ seq --separator="," 10 2 1

No output for above commands.

My shell details:

$ bash --version
GNU bash, version 3.2.25(1)-release (x86_64-redhat-linux-gnu)
Copyright (C) 2005 Free Software Foundation, Inc.

Let me know how I would be able to display the numbers in descending order?

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Answers:

Method 1

Method 2

Method 3

Method 4

Method 5

Method 6

Answers:

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Method 1

use negative increment

seq -s, 10 -2 1
10,8,6,4,2

Method 2

In general, you don’t want to use seq, it’s not portable (even among standard Linux environments). If you’re using ksh, zsh, or bash4+, you can use brace expansion:

echo {10..1..2} | tr " " ,
10,8,6,4,2

Method 3

Another way in pure bash, ksh or zsh:

for ((i=10;i>0;i-=2)) ; do echo -n "$i," ; done

A pure POSIX sh way:

i=10
while [ "$i" -gt 2 ]; do printf "$i,"; i=$((i-2)); done
echo "$i"

Method 4

Now, standard POSIX ones:

awk 'BEGIN{for (i = 10; i > 0; i -= 2) print i}' | paste -sd , -

(interestingly, with mawk (and to a lesser extent gawk as well) a lot faster than GNU seq for i = 10000000 instead of i = 10)

i=10; set --
while [ "$i" -gt 0 ]; do
  set -- "<a href="https://getridbug.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="cbef8b">[email protected]</a>" "$i"
  i=$(($i - 2))
done
IFS=,
echo "$*"

(would only be more efficient with small numbers of iterations, especially with bash)

echo 'for(i=10;i>0;i-=2) i' | bc | paste -sd , -

(which would support numbers of any size, but note that past a certain number of digits (numbers greater than 10⁷⁰ in the POSIX locale at least), lines would be wrapped with backslashes)

Method 5

Try with:

   seq [OPTION]... FIRST INCREMENT LAST

Example:

$ seq 10 -1 1

Method 6

You can reverse the order using tac (cat in reverse). Even if seq should behave differently on various system, I think the following should be as portable as possible:

$ seq 1 10 | tr '12' ',' | sed 's/,$//'; echo
1,2,3,4,5,6,7,8,9,10
$ seq 1 10 | tac | tr '12' ',' | sed 's/,$//'; echo
10,9,8,7,6,5,4,3,2,1
$

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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