shell--variable self-increment

when writing loops in the Linux Shell , it is often necessary to use the variable's self-increment, now summarize the method of increment of integer variable.
As far as I know, in bash, there are currently five ways to do this:
1. i= ' expr $i + 1 ';
2. Let i+=1;
3. ((i++));
4. i=$[$i +1];
5. i=$ (($i + 1))
To practice, the simple examples are as follows:

#!/bin/bash i=0; While [$i-lt 4]; Do echo $i; i= ' expr $i + 1 '; # let I+=1; # ((i++)); # i=$[$i +1]; # i=$ (($i + 1)) Done

In addition, for a fixed number of cycles, can be achieved by the SEQ command, there is no need for the increment of the variable, the example is as follows:

#!/bin/bash For j in $ (SEQ 1 5) Do Echo $j Done

shell--variable self-increment