Linux shell编程学习笔记（四） 位置变量

1、位置变量

也称系统变量或位置参数，是shell脚本运行时，传递给脚本的参数

名称以数字命名，如：$1, $2, ${10}

测试程序如下：

#!/bin/bash
#test.sh
#test var
#by wzs 2017/10/23
echo "the number of parameters is $#"
echo "the return code of last command is $?"
echo "the script name is $0"
echo "the parameters is $*"
echo "\$1 = $1; \$2 = $2"

运行结果如下：

book@wzs:~/work/tq210/shell$ ./test.sh aa bb
the number of parameters is 2
the return code of last command is 0
the script name is ./test.sh
the parameters is aa bb
$1 = aa; $2 = bb

脚本中判断前一个命令的返回值，一般成功返回0，失败返回非0，如下：

#!/bin/bash
#test.sh
#test var
#by wzs 2017/10/23
if [ $# -ne 2 ];
then
        echo "Usage:$0 string files";
        exit 1;
fi

grep $1 $2 -nR;

if [ $? -ne 0 ];
then
        echo "Not found \"$1\" in $2";
        exit 1;
fi

echo "Found \"$1\" in $2";

执行方式一：

book@wzs:~/work/tq210/shell$ ./test.sh xxx bb.txt 
Not found "xxx" in bb.txt

由于在bb.txt文件里没有匹配到"xxx"所以，grep命令返回非0

执行方式二：

book@wzs:~/work/tq210/shell$ ./test.sh a bb.txt 
1:fda
2:afda
Found "a" in bb.txt

匹配到字符"a"，所以grep命令返回值是0