Question

我需要帮助来理解以下代码。为什么N和D在这里使用？他们在这里是什么意思？

这是一个sed命令，用于打印重复的输入行。

sort file | sed '$!N; s/^\(.*\)\n\1$/\1/; t; D'

Answer 1

这是脚本的翻译：

for each line of input:      # sed does this loop automatically

    if it's not the last line:     # This is what $! means

        append a \n (newline) to the current line           # N means this
        append the next line of input to the current line   # and this

    # Note that the "current line" may now contain a \n in the middle!

    if the current line matches some string, followed by a \n,
            followed by that same string again:               # s command's pattern
        delete the \n and the second copy of the string       # s command's action

    if the s command matched:       # t means this
        go to endOfScript           # and this

    delete everything up to the first \n in the current line  # D means this
    go to endOfLoop                                           # and this

  endOfScript:
    print the current line, followed by \n, to stdout    # sed does this automatically

  endOfLoop:
    # just return to the top of the loop for the next line of input

D命令实际上有点复杂：如果当前行还剩下任何字符，它会抑制循环顶部下一行的读取。但是在这个sed脚本中情况并非如此。

Answer 2

根据sed man page，

N指定读取/附加下一行输入到模式中   空间。

D删除模式空间中的第一个嵌入换行符。   开始下一个循环，但如果仍然存在则跳过读取输入   模式空间中的数据。

$匹配最后一行。

!表示它与N
的实际定义不符
t label如果s///已完成替换，那么{。}}   读取了最后一个输入行，然后是上一个t或T命令   分支到标签;如果省略label，则跳转到脚本结尾。

Unix命令理解sed脚本

2 个答案: