bash の for ループ

こうやって書ける

#!/bin/bash

for((i=0;i<5;i++)){
    echo $i
}

スペース入れてもＯＫ

#!/bin/bash

for (( i = 0 ; i < 5 ; i ++ )) {
    echo $i
}

出典
http://qiita.com/b4b4r07/items/e56a8e3471fb45df2f59

man bash 抜粋

for (( expr1 ; expr2 ; expr3 )) ; do list ; done
    First,  the  arithmetic  expression  expr1  is  evaluated according to the rules
    described below under ARITHMETIC EVALUATION.  The arithmetic expression expr2 is
    then evaluated repeatedly until it evaluates to zero.  Each time expr2 evaluates
    to a non-zero value, list is executed and the  arithmetic  expression  expr3  is
    evaluated.   If  any  expression is omitted, it behaves as if it evaluates to 1.
    The return value is the exit status of the last command in  list  that  is  exe-
    cuted, or false if any of the expressions is invalid.

; do list ; done の部分がなんで { list } でいいのか謎。