A, if statement usage
if expression
then
command
be
Examples: integer comparison operators
read -p "please input a integer:" a
if [ "$a" -gt 10 ]
then
echo "The integer which you input is bigger than 10。"
exit 100
be
NOTE: After executing the script, exit command returns an exit status, echo $? You can print the exit status
Two, if / else statement Usage
if expression
then
command
else
command
be
Example: to determine whether a file exists.
IF [-e " $ 1 "] # $ 1 is the location parameter
then
echo "the file $1 is exist"
else
echo "the file is $1 not exist"
be
Three, if / elif / else statement Usage
if expression1
then
command
elif expression2
then
command
elif expression3
then
command
else
command
be
Examples: input points, level determination score
#!/bin/bash
read -p "please input your score:" s
if [ "$s" -ge 90 ]
then
echo "The grade is A!"
exit 1
elif [ "$s" -ge 80 ]
then
echo "The grade is B!"
exit 2
elif [ "$s" -ge 70 ]
then
echo "The grade is C!"
exit 3
elif [ "$s" -ge 60 ]
then
echo "The grade is D!"
exit 4
else
echo "The grade is E!"
exit 5
fi
// running instance
[root@localhost lzic]# ./a.sh
please input your score:90
The grade is A!
[root@localhost lzic]# echo $?
1
[root@localhost lzic]# ./a.sh
please input your score:20
The grade is E!
[root@localhost lzic]# echo $?
5
Three, case usage
case variable in
value1)
command
value2)
command
value3)
command
*)
command
esac