1. if-else语句
#!/bin/bash
#if ... fi 语句;
if [ $a != $b ]
then
echo "a != b"
fi
#if ... else ... fi 语句;
if [ $a == $b ]
then
echo "a is equal to b"
else
echo "a is not equal to b"
fi
#if ... elif ... else ... fi 语句;
if [ $a == $b ]
then
echo "a is equal to b"
elif [ $a -gt $b ]
then
echo "a is greater than b"
elif [ $a -lt $b ]
then
echo "a is less than b"
else
echo "None of the condition met"
fi
2. case-esac语句
#!/bin/bash
read -p "Please input a number" aNum
case $aNum in
1) echo 'You select 1'
;; #不要忘记加上这一行
2) echo 'You select 2'
;;
3) echo 'You select 3'
;;
4) echo 'You select 4'
;;
*) echo 'You do not select a number
between 1 to 4'
;;
esac
3. for循环
#!/bin/bash
#for循环一般格式为:
#for 变量 in 列表
#do
# command1
# command2
# ...
# commandN
#done
#列表是一组值(数字、字符串等)组成的序列,每个值通过空格分隔。每循环一次,就将列表中的下一个值赋给变量。
#in 列表是可选的,如果不用它,for 循环使用命令行的位置参数。
#for loop in 1 2 3 4 5
for loop in 1 2 tt 4 5 kk
do
echo "The value is: $loop"
done
#The value is: 1
#The value is: 2
#The value is: tt
#The value is: 4
#The value is: 5
#The value is: kk
num=0
for str in 'This is a string'
do
num=`expr $num + 1`
echo $str $num #-->This is a string 1 ;只执行一次
done
4. while循环
#!/bin/bash
COUNTER=0
while [ $COUNTER -lt 3 ]
do
COUNTER=`expr $COUNTER + 1`
done
5. until循环
#!/bin/bash
#until 循环执行一系列命令直至条件为 true 时停止。until 循环与 while 循环在处理方式上刚好相反。一般while循环优于until循环,但在某些时候,也只是极少数情况下,until 循环更加有用。
a=0
until [ ! $a -lt 5 ]
do
echo $a #--> 0 1 2 3 4 5
a=`expr $a + 1`
done
6. break,continue跳出循环