shell脚本的流程控制语句的实现

if [ 条件判断式 ];then
程序
fi

if [ 条件判断式 ]
then
程序
fi

[root@hadoop ~]# a=25
[root@hadoop ~]# if [ $a -gt 18 ];then echo OK; fi
OK
[root@hadoop ~]# a=15
[root@hadoop ~]# if [ $a -gt 18 ]; then echo OK; fi

[root@hadoop scripts]# a=25
[root@hadoop scripts]# if [ $a -gt 18 ] && [ $a -lt 35 ];then echo OK;fi
OK

[root@hadoop scripts]# vim if_test.sh
#!/bin/bash
if [ "$1"x = "zhangsan"x ]    #等号左右加x，避免输入空值报错
then
    echo "zhangsan"
fi
[root@hadoop scripts]# . if_test.sh zhangsan
zhangsan
[root@hadoop scripts]# . if_test.sh  
[root@hadoop scripts]# . if_test.sh lisi

[root@hadoop scripts]# a=36
[root@hadoop scripts]# if [ $a -gt 18 ] && [ $a -lt 35 ]; then echo OK; fi
[root@hadoop scripts]# if [ $a -gt 18  &&  $a -lt 35 ]; then echo OK; fi
-bash: [: missing `]'    #不能直接用
[root@hadoop scripts]# if [ $a -gt 18  -a  $a -lt 35 ]; then echo OK; fi
[root@hadoop scripts]# a=20
[root@hadoop scripts]# if [ $a -gt 18  -a  $a -lt 35 ]; then echo OK; fi
OK

if [ 条件判断式 ]
then
程序
elif [ 条件判断式 ]
then
程序
else
程序
fi

[root@hadoop scripts]# vim if_test.sh
#!/bin/bash
if [ "$1"x = "zhangsan"x ]
then
    echo "zhangsan"
fi
#输入第二个参数，表示年龄，判断属于哪个年龄段
if [ $2 -lt 18 ]
then
    echo "未成年人"
else
    echo "成年人"
fi
[root@hadoop scripts]# . if_test.sh zhangsan 15
zhangsan
未成年人
[root@hadoop scripts]# . if_test.sh zhangsan 25
zhangsan
成年人

[root@hadoop ~]# vim case_test.sh
#!/bin/bash
case $1 in
1)
    echo "one"
;;
2)
    echo "two"
;;
3)
    echo "three"
;;
*)
    echo "number else"
;;
esac
[root@hadoop ~]# chmod +x case_test.sh
[root@hadoop ~]# . case_test.sh
number else
[root@hadoop ~]# . case_test.sh 2
two
[root@hadoop ~]# . case_test.sh 1
one
[root@hadoop ~]# . case_test.sh 6
number else

[root@hadoop ~]# vim sum_to.sh
[root@hadoop ~]# cat sum_to.sh
#!/bin/bash
 
sum=0
for (( i=1; i <= $1; i++ ))
do
    sum=$[ $sum + $i ]
done
echo $sum
[root@hadoop ~]# chmod +x sum_to.sh
[root@hadoop ~]# . sum_to.sh 100
5050

[root@hadoop ~]# for i in {1..100}; do sum=$[$sum+$i]; done; echo $sum
5050

[root@hadoop scripts]# vim parameter_for_test.sh
#!/bin/bash
 
echo '============$*================'
for para in $*
do
    echo $para
done
 
echo '============$@================'
for para in $@
do
        echo $para
done
 
[root@hadoop scripts]# chmod +x parameter_for_test.sh 
[root@hadoop scripts]# . parameter_for_test.sh a b c d e
============$*================
a
b
c
d
e
============$@================
a
b
c
d
e

[root@hadoop scripts]# vim parameter_for_test.sh
#!/bin/bash
 
echo '============$*================'
for para in "$*"
do
    echo $para
done
 
echo '============$@================'
for para in "$@"
do
        echo $para
done
 
[root@hadoop scripts]# . parameter_for_test.sh a b c d e
============$*================
a b c d e
============$@================
a
b
c
d
e

[root@hadoop scripts]# vim sum_to.sh 
#!/bin/bash
 
#用for进行实现
sum=0
for (( i=1; i <= $1; i++ ))
do
    sum=$[ $sum + $i ]
done
echo $sum
 
#用while做一个实现
a=1
while [ $a -le $1 ]
do
    sum2=$[ $sum2 + $a ]
    a=$[ $a + 1 ]
done
echo $sum2 
[root@hadoop scripts]# . sum_to.sh 100
5050
5050

[root@hadoop scripts]# vim sum_to.sh 
#用while做一个实现
sum2=0
a=1
while [ $a -le $1 ]
do
#    sum2=$[ $sum2 + $a ]
#    a=$[ $a + 1 ]
    let sum2+=a
    let a++
done
echo $sum2 
[root@hadoop scripts]# . sum_to.sh 100
5050
5050