☰

shell 读取命令行参数 ${1,,} 是什么意思

tag-icon • tag-icon bash variable-substitution parameter
shell 读取命令行参数 ${1,,} 是什么意思

在 Shell 脚本代码中，命令行参数分配给变量，如下所示。语句中的逗号(,)是什么意思。在读取 Bash 脚本中的命令行参数时添加两次逗号会有什么区别。

#!/bin/bash
var1=${1,,}
var2=${2,,}

./script.sh value1 value2

答案1

它是参数扩展被称为案例修改（看man bash）。

$var1将包含第一个参数，所有字符都转换为小写。 Single,只会更改参数的第一个字符。

您可以为逗号后的每个字符指定一个模式，例如以下仅小写元音：

x=$(echo {A..Z})
echo ${x,,[AEIOU]}

输出：

a B C D e F G H i J K L M N o P Q R S T u V W X Y Z

对称地，您可以使用^转换为大写。

答案2

man bash | grep -B1 -A10 ,,
       ${parameter,pattern}
       ${parameter,,pattern}
              Case modification.  This expansion modifies the case  of  alpha‐
              betic  characters in parameter.  The pattern is expanded to pro‐
              duce a pattern just as in pathname expansion.  Each character in
              the  expanded value of parameter is tested against pattern, and,
              if it matches the pattern, its case is converted.   The  pattern
              should  not  attempt  to  match  more than one character.  The ^
              operator converts lowercase letters matching pattern  to  upper‐
              case; the , operator converts matching uppercase letters to low‐
              ercase.  The ^^ and ,, expansions convert each matched character
              in  the expanded value; the ^ and , expansions match and convert
              only the first character in the expanded value.  If  pattern  is
              omitted,  it is treated like a ?, which matches every character.
              If parameter is @ or  *,  the  case  modification  operation  is
              applied  to each positional parameter in turn, and the expansion
              is the resultant list.  If parameter is an array  variable  sub‐
              scripted with @ or *, the case modification operation is applied
              to each member of the array in turn, and the  expansion  is  the
              resultant list.

相关内容