Shell 判斷 if 和分支 case

語法：

if [ 條件判斷式 ];then

# do something
fi

if [ 條件判斷式 ]

then
# do something
fi

#!/bin/bash

test=`env | grep "user" | cut -d
"="-f
2`if [ test=="root" ];then
echo
"this user is root"
fi

#!/bin/bash

rate=`df -h | grep "sda1" | awk '' | cut -d
"%"-f
1`if [ $rate
-gt"10" ];then
echo
"/ is full"
fi

- 條件判斷式就是test命令判斷，可以用test命令替代，中括號中間必須有空格

- -gt 當變數值為空時會報錯

語法：

if [ 條件判斷式 ]

then 
...else
...fi

#!/bin/bash

read -t 30 -p "input a dir:" dir
if [ -d
$dir ]
then
echo
"this is a directory"
else
echo
"no no no "
fi

#!/bin/bash

test=`ps aux | grep tomcat | grep -v grep`
if [ -n "$test" ]
then
echo
"tomcat is running"
else
echo
"tomcat is not running"
/etc/init.d/tomcat start
#                service tomcat start  不建議使用
echo
"tomcat is started"
fi

- if判斷中的變數最好加上引號，因為如果變數的值中包含空格，將出現too many arguments錯誤，所以還是寫成if [ -n "$test" ]較安全

語法：

if [ 條件判斷 ]

then 
# do something
elif [ 條件判斷 ]
then 
# do something
...else
# do something
fi

#!/bin/bash

read -p "please input num1:" num1
read -p "please input operator:" op
read -p "please input num2:" num2
if [ -z "$num1" -o -z "$num2" -o -z "$op" ]
then
echo
"value shoud not be null"
exit
2else
# 把所有數字替換成空,如果替換後不為空，則表示變數中不符合規範 
test1=`echo
$num1 | sed 's/[0-9]//g'`
test2=`echo
$num2 | sed 's/[0-9]//g'`
if [ -n "$test1" -o -n "$test2" ];then
echo
"數值格式錯誤"
exit4fi
if [ "$op" == "+" ]
then
result=$(($num1+$num2))
elif [ "$op" == "-" ]
then
result=$(($num1-$num2))
elif [ "$op" == "*" ]
then
result=$(($num1*$num2))
elif [ "$op" == "/" ]
then
let"result=$num1/$num2"
else
echo
"operator is wrong"
exit3fi
fiecho$$
$=$

#!/bin/bash

read -p "請輸入檔案或目錄名：" path
if [ -z "$path" ]
then
echo
"請輸入內容！"
exit
10elif [ ! -e
"$path" ]
then
echo
"檔案或目錄不存在"
exit
11elif [ -f
"$path" ]
then
echo
"輸入的是乙個檔案"
elif [ -d
"$path" ]
then
echo
"輸入的是乙個目錄"
else
echo
"輸入的式其他型別的檔案"
fi

case $變數名 in

"值1")
// do something,變數的值等於值1
;;"值2")
// do something，變數的值等於值2
;;...
*)// do something，變數的值與上面都不同
;;esca

#!/bin/bash

read -p "請輸入 yes/no" result
case
"$result"
in"yes")
echo
"你輸入的式yes"
;;"no")
echo
"你輸入的是no"
;;*)
echo
"請輸入正確的選擇"
esac

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