bash 中变量名后的 2 个逗号是什么意思？
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What does 2 commas after variable name mean in bash?
提问by user1308345
Recently I came across this syntax:
最近我遇到了这个语法：
${reportName,,}
I could not find anything by googling, so does anyone know what does those ,, mean?
我通过谷歌搜索找不到任何东西，所以有人知道那些 ,, 是什么意思吗？
回答by P....
This is called "Parameter Expansion" available in bash version 4+ . To change the case of the string stored in the variable to lower case.Eg:
这在 bash 版本 4+ 中称为“参数扩展”。将存储在变量中的字符串的大小写更改为小写。例如：
var=HeyThere
echo ${var,,}
heythere
You may want to try some additional commands and check the effect : source
您可能想尝试一些额外的命令并检查效果：源
${var^}
${var^^}
${var,}
${var,,}
Note: "Parameter Expansion" is present in man bash.Search for it.
注意：“参数扩展”存在于man bash.Search 中。
