linux shell脚本学习xargs命令使用详解

我会带着你远行 2023-10-17 15:57 100阅读 0赞

xargs是一条Unix和类Unix操作系统的常用命令。它的作用是将参数列表转换成小块分段传递给其他命令，以避免参数列表过长的问题

xargs是给命令传递参数的一个过滤器，也是组合多个命令的一个工具。它把一个数据流分割为一些足够小的块，以方便过滤器和命令进行处理。通常情况下，xargs从管道或者stdin中读取数据，但是它也能够从文件的输出中读取数据。xargs的默认命令是echo，这意味着通过管道传递给xargs的输入将会包含换行和空白，不过通过xargs的处理，换行和空白将被空格取代。

xargs 是一个强有力的命令，它能够捕获一个命令的输出，然后传递给另外一个命令，下面是一些如何有效使用xargs 的实用例子。  
1. 当你尝试用rm 删除太多的文件，你可能得到一个错误信息：/bin/rm Argument list too long. 用xargs 去避免这个问题

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2. 获得/etc/ 下所有\*.conf 结尾的文件列表，有几种不同的方法能得到相同的结果，下面的例子仅仅是示范怎么实用xargs ，在这个例子中实用 xargs将find 命令的输出传递给ls -l

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3. 假如你有一个文件包含了很多你希望下载的URL, 你能够使用xargs 下载所有链接

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4. 查找所有的jpg 文件，并且压缩它

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5. 拷贝所有的图片文件到一个外部的硬盘驱动

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EXAMPLES  
find /tmp -name core -type f -print | xargs /bin/rm -f  
Find files named core in or below the directory /tmp and delete them. Note that this will work incorrectly if there are any filenames containing newlines or spaces.

find /tmp -name core -type f -print0 | xargs -0 /bin/rm -f  
Find files named core in or below the directory /tmp and delete them, processing filenames in such a way that file or directory names containing spaces or newlines are correctly handled.

find /tmp -depth -name core -type f -delete  
Find files named core in or below the directory /tmp and delete them, but more efficiently than in the previous example (because we avoid the need to use fork(2) and exec(2) to launch rm and we don't need the extra xargs process).

cut -d: -f1 < /etc/passwd | sort | xargs echo  
Generates a compact listing of all the users on the system.

xargs sh -c 'emacs "$@" < /dev/tty' emacs  
Launches the minimum number of copies of Emacs needed, one after the other, to edit the files listed on xargs' standard input. This example achieves the same effect as BSD's -o option, but in a more flexible and portable way.

例如，下面的命令：

复制代码代码如下:

rm \`find /path -type f\`

如果path目录下文件过多就会因为“参数列表过长”而报错无法执行。但改用xargs以后，问题即获解决。

复制代码代码如下:

find /path -type f -print0 | xargs -0 rm

本例中xargs将find产生的长串文件列表拆散成多个子串，然后对每个子串调用rm。-print0表示输出以null分隔（-print使用换行）；-0表示输入以null分隔。这样要比如下使用find命令效率高的多。

复制代码代码如下:

find /path -type f -exec rm '\{\}' \\;

xargs命令应该紧跟在管道操作符之后，它以标准输入作为主要的源数据流，并使用stdin并通过提供命令行参数来执行其他命令，例如：

复制代码代码如下:

command | xargs

实例应用1，将多行输入转换为单行输出：

复制代码代码如下:

amosli@amosli-pc:~/learn$ cat example.txt  
1 2 3 4 5  
6 7  
8  
amosli@amosli-pc:~/learn$ cat example.txt | xargs  
1 2 3 4 5 6 7 8

实例应用2，将单行输入转换为多行输出：

复制代码代码如下:

amosli@amosli-pc:~/learn$ cat example.txt | xargs -n 2  
1 2  
3 4  
5 6  
7 8

空格是默认的定界符，-n 表示每行显示几个参数

还可以使用-d参数来分隔参数,如下：

复制代码代码如下:

amosli@amosli-pc:~/learn$ echo "splitXhiXamosliXsplit" | xargs -d "X" -n 1  
split  
hi  
amosli  
split

实例应用3，读取stdin,将格式化参数传递给命令

复制代码代码如下:

\#定义一个echo命令每次在输出参数后都加上\#  
amosli@amosli-pc:~/learn$ cat cecho.sh  
echo $\*'\#'

＃需求1:输出多个参数  
amosli@amosli-pc:~/learn$ sh cecho.sh arg1  
arg1\#  
amosli@amosli-pc:~/learn$ sh cecho.sh arg2  
arg2\#  
amosli@amosli-pc:~/learn$ sh cecho.sh arg3  
arg3\#

\#需求2：一次性提供所有的命令参数  
amosli@amosli-pc:~/learn$ sh cecho.sh arg1 arg2 arg3  
arg1 arg1 arg2 arg3\#

＃针对需求1、2，使用xargs代替，先用vi建一个新文件args.txt,如下：  
amosli@amosli-pc:~/learn$ cat args.txt  
arg1  
arg2  
arg3  
＃批量输出参数:  
amosli@amosli-pc:~/learn$ cat args.txt | xargs -n 1  
arg1  
arg2  
arg3  
amosli@amosli-pc:~/learn$ cat args.txt | xargs -n 2 sh cecho.sh  
arg1 arg2\#  
arg3\#  
＃一次性输出所有参数：  
amosli@amosli-pc:~/learn$ cat args.txt | xargs sh cecho.sh ;  
arg1 arg2 arg3\#

需求3，如何将参数嵌入到固定的命令行中？如下所示:

复制代码代码如下:

amosli@amosli-pc:~/learn$ sh cecho.sh -p args1 -1  
\-p args1 -1\#  
amosli@amosli-pc:~/learn$ sh cecho.sh -p args2 -1  
\-p args2 -1\#  
amosli@amosli-pc:~/learn$ sh cecho.sh -p args3 -1  
\-p args3 -1\#

使用xargs的解决方案：

复制代码代码如下:

amosli@amosli-pc:~/learn$ cat args.txt | xargs -I \{\} sh cecho.sh -p \{\} -1  
\-p arg1 -1\#  
\-p arg2 -1\#  
\-p arg3 -1\#

＃-I \{\}批定了替换字符串，字符串\{\}会被从stdin读取到的参数所替换，使用－I时，能循环按要求替换相应的参数

实例应用4，结合find使用xargs

前面已经举过例子，这里要注意的是文件名称定界符要以字符null来分隔输出，如下所示，否则可能会误删文件

复制代码代码如下:

amosli@amosli-pc:~/learn$ find . -type f -name "\*test\*.txt" -print0 | xargs -0 rm -f

其他：

复制代码代码如下:

cat file | ( while read arg; do cat $arg; done )  
cat file | xargs -I \{\} cat \{\}

来源:http://www.jb51.net/article/44720.htm