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# **xargs**
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## 说明
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**xargs命令** 是给其他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。它擅长将标准输入数据转换成命令行参数，xargs能够处理管道或者
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stdin并将其转换成特定命令的命令参数。xargs也可以将单行或多行文本输入转换为其他格式，例如多行变单行，单行变多行。xargs的默认命令是echo，
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空格是默认定界符。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是构建单行命令
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的重要组件之一
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## 选项
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```markdown
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xargs [OPTION]... COMMAND INITIAL-ARGS...
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Run COMMAND with arguments INITIAL-ARGS and more arguments read from input.
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非强制性参数以[方括号]表示
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-0, --null Items are separated by a null, not whitespace.
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Disables quote and backslash processing
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-a, --arg-file=FILE Read arguments from FILE, not standard input
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-d, --delimiter=CHARACTER Input items are separated by CHARACTER, not by
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blank space. Disables quote and backslash
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processing
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-E END If END occurs as a line of input, the rest of
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the input is ignored.
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-e [END], --eof[=END] Equivalent to -E END if END is specified.
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Otherwise, there is no end-of-file string
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--help Print a summary of the options to xargs.
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-I R same as --replace=R (R must be specified)
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-i,--replace=[R] Replace R in initial arguments with names
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read from standard input. If R is
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unspecified, assume {}
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-L,-l, --max-lines=MAX-LINES Use at most MAX-LINES nonblank input lines per
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command line
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-l Use at most one nonblank input line per
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command line
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-n, --max-args=MAX-ARGS Use at most MAX-ARGS arguments per command
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line
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-P, --max-procs=MAX-PROCS Run up to max-procs processes at a time
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-p, --interactive Prompt before running commands
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--process-slot-var=VAR Set environment variable VAR in child
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processes
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-r, --no-run-if-empty If there are no arguments, run no command.
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If this option is not given, COMMAND will be
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run at least once.
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-s, --max-chars=MAX-CHARS Limit commands to MAX-CHARS at most
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--show-limits Show limits on command-line length.
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-t, --verbose Print commands before executing them
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--version Print the version number
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-x, --exit Exit if the size (see -s) is exceeded
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```
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## 实例
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```bash
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cat test.txt | xargs -n3 # 多行输出
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echo "nameXnameXnameXname" | xargs -dX # -d选项自定义一个定界符
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echo "nameXnameXnameXname" | xargs -dX -n2 # 读取stdin，将格式化后的参数传递给命令
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ls *.jpg | xargs -n1 -I cp {} /data/images # 复制所有图片文件到 /data/images 目录
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find . -type f -name "*.log" -print0 | xargs -0 rm -f
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find . -type f -name "*.php" -print0 | xargs -0 wc -l # 统计一个源代码目录中所有php文件的行数
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find . -type f -name "*.jpg" -print | xargs tar -czvf images.tar.gz # 查找所有的jpg 文件，并且压缩它们
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cat url-list.txt | xargs wget -c # list.txt包含了很多下载的URL，使用xargs下载所有链接
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```
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