• if 判斷

1. if開(kāi)始判斷,反順序fi結(jié)束
2. if后跟判斷條件,then后跟條件成立后,要執(zhí)行的代碼
3. if不滿足的時(shí)候,則執(zhí)行else
4. elif為當(dāng)上一個(gè)條件不滿足時(shí)才會(huì)執(zhí)行
5. 判斷條件必須以 (()) 包括,不得缺少
6. 判斷條件也可以使用 [] ,但[]和條件之間必須有空格,且條件的判斷不可再使用 < 這些符號(hào),需使用 -lt

7. shell腳本中if還常判斷文件的屬性,使用[ -xxx filename ]

8. shell語(yǔ)句中,一行若要寫(xiě)多條語(yǔ)句,則必須以 ; 分號(hào)分割.若換行,則無(wú)需 ; 分號(hào)結(jié)尾

#! /bin/bash

#Init var
score="Pls input your score :"
exam_not="Sorry ! You didn't pass the exam."
exam_yes="Congratulation ! You pass the exam."

# If
read -p "$score" a
if ((a<60));then
        echo $exam_not
fi

# If & else
read -p "$score" b
if ((b<60));then
        echo $exam_not
else
        echo $exam_yes
fi

# If & else & elif
read -p "$score" c
if ((c<60))
then
        echo $exam_not
elif ((c>=60 && c<=100));then
        echo $exam_yes
else
        echo "Sorry ! The information of you had inputted is wrong !"
fi

# []
d=10;if [ $d -gt 5 ];then echo "Pass !";fi

# File attr
if [ -r test01_if.sh ];then echo "Has !";fi

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• case 分支

1. case可以有無(wú)限個(gè)分支
2. case語(yǔ)句必須以反數(shù)序單詞esac結(jié)束
3. 選項(xiàng)*代表前面的選項(xiàng)不滿足時(shí)執(zhí)行的分支
4. 每個(gè)分支必須以;;結(jié)束

#! /bin/bash
# Judge the number is even or odd !

read -p "Pls input a num : " a
b=$[$a%2]
case $b in
1)
        echo "The num is even !"
        ;;
0)
        echo "The num is odd !"
        ;;
*)
        echo "It is error !"
        ;;
esac

image.png