关于linux命令“xargs”的使用
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About the usage of linux command "xargs"
提问by BlackMamba
I have some file like
我有一些像
love.txt
loveyou.txt
in directory useful; I want to copy this file to directory /tmp.
在目录中useful；我想将此文件复制到目录/tmp。
I use this command:
我使用这个命令：
find ./useful/ -name "love*" | xargs cp /tmp/
but is doesn't work, just says:
但不起作用，只是说：
cp: target `./useful/loveyou.txt' is not a directory
when I use this command:
当我使用这个命令时：
find ./useful/ -name "love*" | xargs -i cp {} /tmp/
it works fine,
它工作正常，
I want to know why the second works, and more about the usage of -i cp {}.
我想知道为什么第二个有效，以及更多关于-i cp {}.
回答by choroba
xargsputs the words coming from the standard input to the end of the argument list of the given command. The first form therefore creates
xargs将来自标准输入的单词放在给定命令的参数列表的末尾。因此，第一种形式创建
cp /tmp/ ./useful/love.txt ./useful/loveyou.txt
Which does not work, because there are more than 2 arguments and the last one is not a directory.
这不起作用，因为有两个以上的参数，最后一个不是目录。
The -ioption tells xargsto process one file at a time, though, replacing {}with its name, so it is equivalent to
该-i选项告诉一次xargs处理一个文件，但替换{}为其名称，因此等效于
cp ./useful/love.txt /tmp/
cp ./useful/loveyou.txt /tmp/
Which clearly works well.
这显然运作良好。
回答by Nathan Fellman
The first example will do this:
第一个示例将执行此操作：
cp /tmp/ love.txt loveyou.txt
Which can't be done, since they attempt to copy the directory /tmpand the file love.txtto the file loveyou.txt.
这是无法完成的，因为他们试图将目录/tmp和文件复制love.txt到文件loveyou.txt.
In the second example, -itells xargsto replace every instance of {}with the argument, so it will do:
在第二个例子中，-i告诉用参数xargs替换每个实例{}，所以它会这样做：
cp love.txt /tmp/
cp loveyou.txt /tmp/
回答by Erik A. Brandstadmoen
When using the xargs -icommand, {}is substituted with each element you find. So, in your case, for both "loveyou.txt" and "love.txt", the following command will be run:
使用该xargs -i命令时，{}将替换为您找到的每个元素。因此，在您的情况下，对于“loveyou.txt”和“love.txt”，将运行以下命令：
cp ./useful/loveyou.txt /tmp/
cp ./useful/love.txt /tmp/
if you omit the {}, all the elements you find will automatically be inserted at the end of the command, so, you will execute the nonsensical command:
如果省略{}，您找到的所有元素将自动插入到命令的末尾，因此，您将执行无意义的命令：
cp /tmp/ ./useful/loveyou.txt ./useful/love.txt
回答by Graham Griffiths
xargs appends the values fed in as a stream to the end of the command - it does not run the command once per input value. If you want the same command run multiple times - that is what the -i cp {} syntax is for.
xargs 将作为流输入的值附加到命令的末尾 - 它不会为每个输入值运行一次命令。如果您希望多次运行相同的命令 - 这就是 -i cp {} 语法的用途。
This works well for commands which accept a list of arguments at the end (e.g. grep) - unfortunately cp is not one of those - it considers the arguments you pass in as directories to copy to, which explains the 'is not a directory' error.
这适用于在末尾接受参数列表的命令（例如 grep） - 不幸的是 cp 不是其中之一 - 它认为您传入的参数作为要复制到的目录，这解释了“不是目录”错误.
回答by jlliagre
You might avoid xargs that way:
你可以这样避免 xargs ：
find ./useful/ -name "love*" -exec sh -c 'cp "$@" /tmp' sh {} +
回答by user3581131
find ./useful/ -name "love*" | xargs cp -t /tmp/
