Bash变量扩展中的'/'

Question

在一个while read line循环里，我看到这个变量扩展 ${line/device name:}。我尝试用自己的输入文件运行脚本，它只是打印出该行。你能告诉我这个扩展是做什么的吗？

- Jimbo

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两个答案都是正确的，但这里有关于参数扩展的文档，以供日后参考和编辑到答案中：http://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html - Jeff Bowman

Answer 1

变量名是 line。/ 用于字符串替换，即如果在 $line 中任何位置存在 "设备名称："，则将其移除。

> line="a device name: some name"
> echo ${line/device name:}
a  some name

您可能还会看到#和%替换，它们代表行的开头和结尾的替换。请注意，这种/替换是bash特有的功能（例如，ash不支持它，%和#似乎是可移植的），因此您应该在脚本开头使用#!/bin/bash而不是#!/bin/sh作为哈希标记。

- user3159253

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%和#确实是可移植的，它们是POSIX shell规范的一部分。 - chepner

谢谢。答案很好！ - Jimbo

Answer 2

它返回去除子字符串“device name:”后的$line。来自Bash手册页面：

${parameter/pattern/string}
       Pattern substitution.  The pattern is expanded to produce a pattern just as in
       pathname  expansion.   Parameter  is expanded and the longest match of pattern
       against its value is replaced with string.  If  pattern  begins  with  /,  all
       matches of pattern are replaced with string.  Normally only the first match is
       replaced.  If pattern begins with #, it must match at  the  beginning  of  the
       expanded  value  of parameter.  If pattern begins with %, it must match at the
       end of the expanded value of parameter.  If string is null, matches of pattern
       are  deleted and the / following pattern may be omitted.  If parameter is @ or
       *, the substitution operation is applied to each positional parameter in turn,
       and  the  expansion  is the resultant list.  If parameter is an array variable
       subscripted with @ or *, the substitution operation is applied to each  member
       of the array in turn, and the expansion is the resultant list.

- John Kugelman

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谢谢。非常好的答案！ - Jimbo