问题描述
考虑这个命令:
ls /mydir/*.txt | xargs chown root
目的是将mydir中所有文本文件的所有者更改为root
The intention is to change owners of all text files in mydir to root
问题是，如果 mydir 中没有 .txt 文件，那么 xargs 会报错，说没有指定路径.这是一个无害的示例，因为正在引发错误，但在某些情况下，例如在我需要在此处使用的脚本中，假定当前目录为空白路径.因此，如果我从 /home/tom/ 运行该命令，那么如果 ls/mydir/*.txt 和 /home/下的所有文件都没有结果tom/ 已将其所有者更改为 root.
The issue is that if there are no .txt files in mydir then xargs thows an error saying there is no path specified. This is a harmless example because an error is being thrown, but in some cases, like in the script that i need to use here, a blank path is assumed to be the current directory. So if I run that command from /home/tom/ then if there is no result for ls /mydir/*.txt and all files under /home/tom/ have their owners changed to root.
那么如何让 xargs 忽略空结果?
So how can I have xargs ignore an empty result?
推荐答案
对于 GNU xargs，可以使用 -r 或 --no-run-if-empty 选项:
For GNU xargs, you can use the -r or --no-run-if-empty option:
--no-run-if-empty -r 如果标准输入不包含任何非空格，请不要运行该命令.通常，即使没有输入，该命令也会运行一次.此选项是 GNU 扩展.
--no-run-if-empty
-r If the standard input does not contain any nonblanks, do not run the command. Normally, the command is run once even if there is no input. This option is a GNU extension.
xargs 的 BSD 版本在 macOS 上使用，不会对空输入运行命令，因此不需要 -r 选项(也不需要它被那个版本的 xargs 接受).
The BSD version of xargs, which is used on macOS, does not run the command for an empty input, so the -r option is not needed (nor is it accepted by that version of xargs).