for ((i=0; i<5; i++)); do echo current: $i; done

# current: 0
# current: 1
# current: 2
# current: 3
# current: 4

# GNU bash, version 3.1.16(1)-release (i686-pc-linux-gnu)
# Copyright (C) 2005 Free Software Foundation, Inc.

# current: 0
# current: 1
# current: 2
# current: 3
# current: 4

# GNU bash, version 3.1.17(1)-release (i686-pc-linux-gnu)
# Copyright (C) 2005 Free Software Foundation, Inc.