三剑客-sed执行流程是怎样的？老男孩Linux培训班

发布时间：2025-11-04 12:35:25 来源：技术快报 作者：系统运维

一. 简易流程

1.读取文件(从文件或管道)的剑客第1行

2.读取到sed使用的内存区域中（模式空间）

1.如果是则则执行对应的命令(p d c a i s )

二.详细执行过程

详细过程一定要看官方的说明：info sed

sed maintains two data buffers: the active *pattern* space, and the auxiliary *hold* space. Both are initially empty. ¨K10K sed operates by performing the following cycle on each line of

sed命令的执行过程（一个循环过程）如下所示:

first, sed reads one line from the input stream, removes any trailing newline, and places it in the pattern space. ¨K14K Then commands are executed; each command can have an address associated to it:addresses are a kind of condition code, and a command is only executed if the condition is verified before the command is to be executed. ¨K16K When the end of the script is reached, unless the-n option is in

use, the contents of pattern space are printed out to the output

stream, adding back the trailing newline if it was removed.(1) Then the

第3步，当命令执行完成（这里命令指的服务器租用行流训班是sed内部的p d s c a i 等等），如果没有-n参数（取消sed命令默认输出）则sed会把当前模式空间的程样内容显示出来然后再加上1个回车（第1步被删除的）.然后开始读取下一行，进行下一个循环.

Unless special commands (like D) are 男孩used, the pattern space is deleted between two cycles. The hold space, on the other hand, keeps its data between cycles (see commandsh, H,x, g,G to move

补充说明:

模式空间的内容会在每个循环结束后清空（除非加上D）。

(1) Actually, if sed prints a line without the terminating newline, it will nevertheless print the missing newline as soon as more text is sent to the same output stream, which gives the "least expected surprise" even though it does not make commands like `sed -n p exactly identical to cat.

实际上，源码下载sed如果显示没有回车的行流训班行，他会在你多次显示到相同输出的程样时候替你加上缺少的回车。这个特点sed -n p 和cat并不完全相同.

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