1. if语句
if语句形式:
If condition
then
statement(s)
fi
If condition;then
statement(s)
fi
请注意condition后面的分号;,当if和then位于同一行时候,这个分号是必须的,否则会有语法错误。
#!/bin/bash
username=student
if grep $username /etc/passwd
then
echo The bash files for user $username are:
ls -a /home/$username/.b*
fi
结果:
student❌1000:1000:Student User:/home/student:/bin/bash
The bash files for user student are:
/home/student/.bash_logout /home/student/.bashrc
/home/student/.bash_profile
#!/bin/bash
read a
read b
if (($a==$b))
then
echo "a和b相等"
fi
结果:
[root@localhost 2-12]# sh 04.sh
3
3
a和b相等
2. if-else语句
格式:
if condition
then
statement1
else
statement2
fi
如果condition成立,那么then后边的statement1语句将会被执行;否则,执行else后面的statement2语句。
read a
read b
if (($a==$b))
then
echo "a和b相等"
else
echo "a和b不相等"
fi
结果:
2
4
a和b不相等
3. if-elif-else语句
格式:
if conditionn1
then
statement1
elif condition2
then
statement2
elif condition3
then
statement3
....
else
ststement
fi
注意:if和elif后面都得跟着then
#!/bin/bash
read age
if (($age<=18));then
echo "未成年"
elif (($age>18 && $age<=60));then
echo "成年"
else
echo "老年"
fi
结果:
33
成年