猫/ xargs的/命令为VS /庆典/命令 [英] cat/Xargs/command VS for/bash/command

问题描述

这本书的Linux黑客101的第38页显示：

The page 38 of the book Linux 101 Hacks suggests:

cat url-list.txt | xargs wget –c

我通常做的：

for i in `cat url-list.txt`
   do
      wget -c $i
   done

有一些事，莫过于长，其他地方的xargs-技术优于老的好 - 环 - 技术在bash？

Is there some thing, other than length, where the xargs-technique is superior to the old good for-loop-technique in bash?

添加

的的 C源$ C ​​$ C 好像只有一个叉。相比之下，多少叉有与bash组合？请，阐述这一问题。

The C source code seems to have only one fork. In contrast, how many forks have the bash-combo? Please, elaborate on the issue.

推荐答案

从的在UNIX联机帮助页的xargs 。 （有趣的是这一节不会出现在的xargs 的OS X版本的BSD，也不在GNU版本）。

From the Rationale section of a UNIX manpage for xargs. (Interestingly this section doesn't appear in the OS X BSD version of xargs, nor in the GNU version.)

在xargs的的典型应用
  实用程序是在与结合
  找到工具来减少数量
  通过一个简单的使用启动的进程
  的发现-exec组合。该
  xargs的效用还用于执行
  内存上限要求
  启动一个进程。随着此基础上
  没关系，这个量POSIX.1-2008的
  只选择了最小的功能
  必需的。

The classic application of the xargs utility is in conjunction with the find utility to reduce the number of processes launched by a simplistic use of the find -exec combination. The xargs utility is also used to enforce an upper limit on memory required to launch a process. With this basis in mind, this volume of POSIX.1-2008 selected only the minimal features required.

在您的随访中，你问另一个版本将会有多少叉有。 <一href=\"http://stackoverflow.com/questions/1282697/cat-xargs-command-vs-for-bash-command/1282713#1282713\">Jim已经回答了这个：在每次迭代之一。多少次迭代有哪些？这是不可能给出一个确切的数字，但容易回答一般问题。在您的网址，LIST.TXT文件有多少行有哪些？

In your follow-up, you ask how many forks the other version will have. Jim already answered this: one per iteration. How many iterations are there? It's impossible to give an exact number, but easy to answer the general question. How many lines are there in your url-list.txt file?

有其他一些其他考虑。 的xargs 需要格外小心与空格或其他无任何字符，而 -exec 文件名有一个选项（ + ），这组加工成批次。所以，不是每个人都prefers 的xargs ，也许它不是最好的所有情况。

There are other some other considerations. xargs requires extra care for filenames with spaces or other no-no characters, and -exec has an option (+), that groups processing into batches. So, not everyone prefers xargs, and perhaps it's not best for all situations.

请参阅以下链接：

• http://www.sunmanagers.org/pipermail/summaries/ 2005年三月/ 006255.html


• http://fahdshariff.blogspot.com/2009/ 05 /查找-EXEC-VS-xargs.html

• http://www.sunmanagers.org/pipermail/summaries/2005-March/006255.html
• http://fahdshariff.blogspot.com/2009/05/find-exec-vs-xargs.html

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