sed命令:如果存在则如何替换，只需插入? [英] Sed command : how to replace if exists else just insert?

问题描述

我需要在文件中编辑几行，以便 如果一行以(av或avpgw)开头，则将其替换为新文本， 否则，只需在开头插入新文本即可.

I need to edit several lines in a file such that if a line begins with (av or avpgw) then replace these with new text, else just insert the new text in beginning.

如何使用sed执行此操作?

How can I do this using sed ?

推荐答案

您可以这样做:

sed -e 's/^avpgw/new text/' -e t -e 's/^av/new text/' -e t -e 's/^/new text/' file

这用new text(s///)替换了模式，并跳到了结尾(t).否则，它将尝试下一个模式.另请参见 sed命令摘要.

This replaces the pattern with new text (s///) and jumps to the end (t). Otherwise it tries the next pattern. See also sed commands summary.

您还可以使用;分隔命令:

You can also separate the commands with ;:

sed 's/^avpgw/new text/; t; s/^av/new text/; t; s/^/new text/' file

或将命令放在sed命令文件中:

or put the commands in a sed command file:

s/^avpgw/new text/
t
s/^av/new text/
t
s/^/new text/

并这样称呼:

sed -f commandfile file

如果要忽略大小写，请像s/^av/new text/i一样在替代命令的末尾附加一个i.另一种方法是使用字符集s/^[aA][vV]/new text/进行拼写.但这不是sed特有的，为此，您通常可以搜索正则表达式.

If you want to ignore case, append an i at the end of the substitute command as in s/^av/new text/i. Another way is to spell it out with character sets s/^[aA][vV]/new text/. But that is not sed specific, for this you can search for regular expressions in general.

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