for循環

for var in list;

do

　　commands;#使用變量$var

done

example:

　　for i in {a..z}; do actions; done;

後者

for((i=0;i<10;i++))

{

　　commands;

}

while condition

do

　　commands;

done

until循環

example:

x=0;

until [ $x -eq 9 ];

do

　　let x++; echo $x;

done

if比較語句

if contions;

then

　　commands;

if

else if和else語句

if condition;

then

　　commands;

else if conditon;then

　　commands;

else

　　commands;

fi

簡潔用法：

[ condition ] && action;

[ condition ] || action;

算數比較：
[ $var -eq 0 ]

[ $var -ne 0 ]

邏輯與和邏輯或

[ $var1 -ne 0 -a $var2 -gt 2 ]

[ $var1 -ne 0 -o $var2 -gt 2 ]

example:

#!/bin/bash
#filename:compare.
 
sh
fpath="/etc/passwd"
if [ -e $fpath ]; then
    echo file exits;
else
    echo does not exists;
fi

shell腳本6--循環，比較