Bash（GNU Bourne-Again Shell）is a Unix shell and script language written by Brian Fox for the GNU Project as a free software replacement for the Bourne shell. First released in 1989, it has been used as the default login shell for most Linux distributions.

〇、从“Hello World”程序开始！

下面是一个简单的“Hello World”程序，但是我们利用一个while循环来执行5次字符串输入语句（如何编写循环语句，我们会在后续文章中详细解释）：

x=1
while [ $x -le 5 ]
do
    echo "Hello World"
    x = $(($x+1))
done

编辑好脚本文件（例如脚本文件名为mybash1.sh）之后，在命令行窗口使用sh mybash1.sh可以执行该脚本程序，如下图所示：

With bash, use -x to echo commands before they are executed and -n to check commands for syntax without executing them. 例如：