linux - 正则表达式 - 在第一次匹配后追加

Question

假设我有以下类型的文件:

a a c
b b c
c c c
d d c
e e c
a a c
b b c
c c c
d d c
e e c

我如何结束:

a a c
b b c
c c c
—————
d d c
e e c
a a c
b b c
c c c
d d c
e e c

...不只是在第 3 行之后添加 em 破折号(第一行带有 c c c)。

Answer 1

这个 awk 可以工作:

awk '1; !flag && /c c c/ { flag = 1; print "—————" }' filename

即:

1                   # first, print every line (1 meaning true here, so the
                    # default action -- printing -- is performed on all
                    # lines)
!flag && /c c c/ {  # if the flag is not yet set and the line we just printed
                    # matches the pattern:
  flag = 1          # set the flag
  print "—————"     # print the dashes.
}

或者使用 sed(尽管我推荐使用 awk 解决方案):

sed -n 'p; /c c c/ { x; /^$/ { s//—————/; p }; x }' filename

这有点复杂。知道一开始保持缓冲区是空的:

p             # print the line
/c c c/ {     # if it matches the pattern:
  x           # exchange hold buffer and pattern space
  /^$/ {      # if the pattern space (that used to be the hold buffer) is
              # empty:
    s//—————/ # replace it with the dashes
    p         # print them
  }
  x           # and exchange again. The hold buffer is now no longer empty,
              # and the dash block will not be executed again.
}