一 語法 if [ 條件判斷式 ] then 當條件判斷式1成立時，執行程式1 elif[ 條件判斷式2 ] then 當條件判斷式2成立時，執行程式2 省略更多條件 else 當所有條件都不成立時，最後執行程式 fi 二 實現計算器 #!/bin/bash read -t 30 -p "please input num1:" num1 read -t 30 -p "please input num2:" num2 read -t 30 -p "please input a operator:" ope if [ -n "$num1" -a -n "$num2" -a -n "$ope" ] then test1=$(echo $num1|sed 's/[0-9]//g') test2=$(echo $num2|sed 's/[0-9]//g') if [ -z "$test1" -a -z "$test2" ] then if [ "$ope" == "+" ] then sum=$(($num1 + $num2)) elif [ "$ope" == "-" ] then sum=$(($num1 - $num2)) elif [ "$ope" == "*" ] then sum=$(($num1 * $num2)) elif [ "$ope" == "/" ] then sum=$(($num1 / $num2)) else echo "Please enter a valid symbol" exit 10 fi else echo "please input a num" exit 11 fi else echo "please input a content:" exit 12 fi echo "$num1 $ope $num2 : $sum" 三 測試 please input num1:re please input num2:23 please input a operator:1 please input a num [[email protected] shell]# echo $? 11 [[email protected] shell]# ./shell5.sh please input num1: please input num2: please input a operator: please input a content: [[email protected] shell]# echo $? 12 [

[email protected] shell]# ./shell5.sh please input num1:12 please input num2:23 please input a operator:gf Please enter a valid symbol [[email protected] shell]# echo $? 10 [[email protected] shell]# ./shell5.sh please input num1:32 please input num2:12 please input a operator:- 32 - 12 : 20 [

[email protected] shell]# ./shell5.sh please input num1:76 please input num2:45 please input a operator:* 76 * 45 : 3420 [[email protected] shell]# ./shell5.sh please input num1:87 please input num2:56 please input a operator:/ 87 / 56 : 1 [[email protected] shell]# ./shell5.sh please input num1:45 please input num2:23 please input a operator:+ 45 + 23 : 68 四 判斷使用者輸入的是什麼檔案 #!/bin/bash read -t 30 -p "please input a file name:" file if [ -z "$file" ] then echo "qing shuru neirong" exit 11 elif [ ! -e "$file" ] then echo "qing shuru wenjianming" exit 12 elif [ -f "$file" ] then echo "$file is a regular file" elif [ -d "$file" ] then echo "$file is a mulu" else echo "$file is another file" fi