bash - bash 中带有变量、大括号和散列字符的 ${0##...} 语法是什么意思？

Question

我刚刚在 bash 中看到了一些我不太理解的代码。作为新手 bash 脚本编写者，我不确定发生了什么。

echo ${0##/*}
echo ${0}

我真的看不出这两个命令的输出有什么不同(打印脚本名称)。 # 只是一条评论吗？ /* 有什么用。如果是注释，它怎么不干扰结束 } 大括号？

谁能给我一些关于这个语法的见解？

Answer 1

参见 Substring removal 部分在 parameter expansion page of the bash-hackers' wiki 上:

${PARAMETER#PATTERN} and ${PARAMETER##PATTERN}

This form is to remove the described pattern trying to match it from the beginning of the string. The operator # will try to remove the shortest text matching the pattern, while ## tries to do it with the longest text matching.

Example string (just a quote from a big man):

MYSTRING="Be liberal in what you accept, and conservative in what you send"

Syntax	Result
${MYSTRING#*in}	Be liberal in what you accept, and conservative in what you send.
${MYSTRING##*in}	Be liberal in what you accept, and conservative in what you send.