查找，替換或插入-命令行

Question

我有類似的清單：

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“ connecting”上找到匹配項並替換行：

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

這應該將上面的列表更改為：

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：

如果存在包含單詞connecting ，則替換該行；如果該行不存在，則將其作為新行添加到列表的末尾。

我知道我可以執行echo "Import a text file by opening it" >> list ，這會將行添加到列表的末尾，但是無論如何，我可以在一個命令中執行此操作嗎？ 還是可以在一個實例中運行的命令？

謝謝

Answer 1

一種簡單的方法是使用awk ：

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

如下所示：

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.
  }
}

另外，您可以使用sed的保持緩沖區。 例如：

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

其工作原理如下：

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.
}

請注意， sed代碼取決於以下事實：只有一行包含“ connecting”。 如果有更多這樣的行，則將它們替換為空行，因為當第二行出現時，保持緩沖區為空。 可以處理這種情況，但是您必須決定在其中應該發生什么。 既然您在評論中回答說只有這樣一行，所以我不需要猜測。

Answer 2

您可以使用與sed類似的正則表達式語法嘗試perl ，但對這些問題的功能要強大得多。 只要完成至少一個替換，它就簡單地設置一個標志。 解析完整個文件后，如果未設置$flag變量，請在END {}塊中添加注釋：

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

找到該行后，將產生：

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

當找不到它時，將產生：

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

如果出現多次，請同時更改兩者，但不添加任何內容：

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