How do I iterate over a range of numbers defined by variables in Bash?

Question

How do I iterate over a range of numbers in Bash when the range is given by a variable?

I know I can do this (called \"sequence expression\" in the Bash documentatio

Answer 1

There are many ways to do this, however the ones I prefer is given below

Using seq

Synopsis from man seq

$ seq [-w] [-f format] [-s string] [-t string] [first [incr]] last

Syntax

Full command
seq first incr last

• first is starting number in the sequence [is optional, by default:1]
• incr is increment [is optional, by default:1]
• last is the last number in the sequence

Example:

$ seq 1 2 10
1 3 5 7 9

Only with first and last:

$ seq 1 5
1 2 3 4 5

Only with last:

$ seq 5
1 2 3 4 5

Using {first..last..incr}

Here first and last are mandatory and incr is optional

Using just first and last

$ echo {1..5}
1 2 3 4 5

Using incr

$ echo {1..10..2}
1 3 5 7 9

You can use this even for characters like below

$ echo {a..z}
a b c d e f g h i j k l m n o p q r s t u v w x y z

Answer 2

This works fine in bash:

END=5
i=1 ; while [[ $i -le $END ]] ; do
    echo $i
    ((i = i + 1))
done