查找、替换或插入 - 命令行

Question

我有一个类似的列表：

What do you want to do?
Import a text file by opening it in Excel
Import a text file by connecting to it
Export data to a text file by saving it
Change the delimiter that is used in a text file
Change the separator in all .csv text files

使用 SED 我可以在“连接”上找到匹配项并替换该行：

 sed 's^.*connecting.*^Import a text file by opening it^g' crontab

这应该将上面的列表更改为：

What do you want to do?
Import a text file by opening it in Excel
Import a text file by opening it
Export data to a text file by saving it
Change the delimiter that is used in a text file
Change the separator in all .csv text files

但是我需要做的是：

如果存在包含单词connecting 的行，则替换该行， 如果该行不存在，则将其作为新行添加到列表的末尾。

我知道我可以做echo "Import a text file by opening it" >> list，这会将行添加到列表的末尾，但是无论如何我可以在一个命令中做到这一点吗？还是可以在一个实例中运行的命令？

谢谢

Answer 1

一个简单的方法是使用awk:

awk 'BEGIN { s = "Import a text file by opening it" } /connecting/ { $0 = s; n = 1 } 1; END { if(!n) print s }' filename

工作原理如下：

BEGIN {                                    # Before anything else:
  s = "Import a text file by opening it"   # Remember the string by a shorter
                                           # name so we don't have to repeat it
}
/connecting/ {                             # If a line contains "connecting",
  $0 = s                                   # replace the line with that string
  n = 1                                    # and raise a flag that we've done so.
}
1                                          # print
END {                                      # in the end:
  if(!n) {                                 # If the string wasn't yet printed,
    print s                                # do it now.
  }
}

或者，您可以使用sed 的保持缓冲区。例如：

sed '1 { x; s/.*/Import a text file by opening it/; x; }; /connecting/ { s/.*//; x; }; $ { G; s/\n$//; }' filename

它的工作原理如下：

1 {                                        # while processing the first line
  x                                        # swap hold buffer, pattern space
  s/.*/Import a text file by opening it/   # write text to pattern space
  x                                        # swap back.
}                                          # Now the hold buffer contains the
                                           # line we want to insert, and the
                                           # pattern space the first line.

/connecting/ {                             # For all lines: If a line contains
                                           # "connecting"
  s/.*//                                   # empty the pattern space
  x                                        # swap in hold buffer.
                                           # If this happened, the hold buffer
                                           # will be empty and the pattern space
                                           # will contain "Import a ..."
}
$ {                                        # Last line:
  G                                        # Append hold buffer to pattern space.
                                           # If the hold buffer is empty (i.e.,
                                           # was used somewhere else), this
                                           # appends a newline, so
  s/\n$//                                  # remove it if that happened.
}

请注意，sed 代码取决于只有一行包含“连接”这一事实。如果有更多这样的行，它们将被替换为空行，因为当第二行出现时，保持缓冲区是空的。可以处理这种情况，但您必须决定其中应该发生什么。由于您在 cmets 中回答只有这样的一行，所以我觉得没有必要猜测。

Answer 2

您可以尝试perl，它使用与sed 类似的正则表达式语法，但对这些问题更强大。当至少完成一次替换时，它只是设置一个标志。解析整个文件后，在END {}块中，如果$flag变量还没有设置，添加注释：

perl -pe '
    s/^.*connecting.*$/Import a text file by opening it/ and $done = 1;
    END { printf qq|%s\n|, q|Import a text file by opening it| unless $done }
' infile

当找到该行时，它产生：

What do you want to do?
Import a text file by opening it in Excel
Import a text file by opening it
Export data to a text file by saving it
Change the delimiter that is used in a text file
Change the separator in all .csv text files

当它没有找到时，它产生：

What do you want to do?
Import a text file by opening it in Excel
Export data to a text file by saving it
Change the delimiter that is used in a text file
Change the separator in all .csv text files
Import a text file by opening it

如果出现不止一次，则同时更改，但不附加任何内容：

What do you want to do?
Import a text file by opening it in Excel
Import a text file by opening it
Export data to a text file by saving it
Change the delimiter that is used in a text file
Import a text file by opening it
Change the separator in all .csv text files