zsh:命令替换和正确引用 [英] zsh: Command substitution and proper quoting

问题描述

我有一个脚本 P 接受文件名作为参数:

I have a script P which accepts file names as parameters:

P file1 file2 file3 ....

我还有一个脚本 G ，它生成一个文件名(通常是短列表)，每行一个文件名.在我想用 zsh 编写的主脚本中，我想使用 G 生成要由 P 处理的文件名.天真的尝试是这样的:

I also have a script G which generates a (typically short list) of file names, one file name per line. In a master script which I would like to write in zsh, I want to use G to generate the file names to be processed by P. The naive attempt goes like this:

P $(G)

这几乎很好用，只是我生活在一个恶意的人喜欢创建带有嵌入空间的文件的世界.如果 G 会生成这样的文件列表:

This works nearly well, only that I'm living in a world where malicious people enjoy creating files with embedded spaces. If G would generate the list of files like this:

one_file 
a file with spaces

P 将被称为

P one_file a file with spaces

代替

P 'one_file' 'a file with spaces'

一个明显的解决方案是将 G 和 P 粘合在一起，而不是通过命令替换，而是通过某种语言(Ruby、Perl、Python、Algol68、....)，它执行 P 的 exec 并将参数传递给从 stdin 读取.

One obvious solution would be to glue G and P together not by command substitution, but by a small program in some language (Ruby, Perl, Python, Algol68,....), which does an exec of P and passes the parameters to a read from stdin.

编写起来很简单，甚至可以重复使用.但是，我想知道 zsh 是否没有内置的解决方案来解决这个问题?

This would be trivial to write and could even be made reusable. However, I wonder, whether zsh with its grabbag of goodies would not have a solution for this problem builtin?

推荐答案

这可以通过:

P ${(f)"$(G)"}

将调用 P as

P 'one_file' 'a file with spaces'

如果G的输出是

one_file
a file with spaces

说明:

$(G) 周围的双引号告诉 zsh 将 G 的输出作为一个词(在 shell 的意义上)字字).

The double quotes around $(G) tell zsh to take the output of G as one word (in the shell sense of the word word).

所以就打电话

P "$(G)"

相当于

P 'one_file
a file with spaces'

这是参数扩展标志 f 发挥作用的地方.${(f)SOMEVAR} 告诉 zsh 在换行符处将 $SOMEVAR 拆分成单词.除了参数(如 SOMEVAR)，还可以在 ${...} 中使用命令替换(此处为 $(G))键入参数表达式，这会导致命令 P ${(f)"$(G)"}.

This is where the Parameter Expansion Flag f comes into play. ${(f)SOMEVAR} tells zsh to split $SOMEVAR into words at newlines. Instead of a parameter (like SOMEVAR) one can also use a command substitution (here $(G)) inside ${...} type parmeter expressions, which leads to the the command P ${(f)"$(G)"}.

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