## 1.語法 if..then..elif..fi的語法： ``` if [ 條件語句 ]；then 執行內容 elif [ 條件語句 ]；then 執行內容 else 執行內容 fi # 或 if [ 條件語句 ] then 執行內容 elif [ 條件語句 ] then 執行內容 else 執行內容 fi ``` ## 2.案例 1.if..then..elif..fi的案例，比較兩個值是否相等。 ``` #!/bin/bash a=10 b=20 if [ $a -eq $b ] then echo "a is equal to b" elif [ $a -gt $b ] # a 大于 b 見表1 then echo "a is greater than b" elif [ $a -lt $b ] # a 小于 b 見表1 then echo "a is less than b" else echo "None of the condition met" fi ``` 文件比較符，表1。 | \[ \]括號 | （（））擴容 | 含義 | | :--- | :--- | :--- | | -eq | == | 等于 | | -ne | != | 不等于 | | -gt | > | 大于 | | -ge | >= | 大于等于 | | -lt | < | 小于 | | -le | <= | 小于等于 | 2.通過條件語句實現的計算器。 ``` #!/bin/bash # author:djangwoang # filename:jisuanqi.sh echo "please input your first number" read a echo "please input + - * /" read b echo "please input your second number" read c if [ "x$b" == "x" ];then echo "please input + - * /" elif [ "$b" == "+" ];then tmp=$((a+c)) elif [ "$b" == "-" ];then tmp=$((a-c)) elif [ "$b" == "*" ];then tmp=$((a*c)) elif [ "$b" == "/" ];then tmp=$((a/c)) else echo "please input + - * /" fi echo "result is:${tmp}" ```