shell expr用法

expr 计算整数变量值

使用方法如下：

linux-zpycfm:/home/test/shell # s=expr +
-bash: +: command not found
linux-zpycfm:/home/test/shell # s=expr +
-bash: +: command not found
linux-zpycfm:/home/test/shell # s=`expr  + `
linux-zpycfm:/home/test/shell # echo $s

linux-zpycfm:/home/test/shell # `expr  + `
-bash: : command not found
linux-zpycfm:/home/test/shell # expr  + 

linux-zpycfm:/home/test/shell # expr +
+
linux-zpycfm:/home/test/shell # expr $s *
expr: syntax error
linux-zpycfm:/home/test/shell # expr $s \* 

linux-zpycfm:/home/test/shell # expr `expr  + ` \* 

linux-zpycfm:/home/test/shell # expr  "*" 

linux-zpycfm:/home/test/shell # expr  '*' 

linux-zpycfm:/home/test/shell # expr  *
expr: syntax error
linux-zpycfm:/home/test/shell # expr 2.3 + 3.4
expr: non-integer argument

运算符号和参数之间要有空格分开；

通配符号(*),在作为乘法运算符时要用\、“”、‘’符号修饰

–:expr 3 \* 2         expr 3 “*” 2       expr 3 ‘*’ 2 

 `(反引号)与键盘上的~同一个键上的符号