In Emacs, How to replace only on matching lines

Question

For example: In VIM,

test
sample replace
test1
replace
sample test2

:g/sample/s/replace/test3/ - will replace "replace" only on matching lines with "sample"

test
sample test3
test1
replace
sample test2

In VIM, to replace only on non-matching lines can be done by :v/sample/s/replace/test3 - will replace "replace" only on non-matching lines which does not contain "sample"

test
sample replace
test1
test3
sample test2

How can above thing can be accomplished using emacs?

Answer 1

Are you using Emacs 24 perchance? If so, you can use the built-in occur-edit-mode:

• First use one of the occur functions to obtain a buffer of lines matching your pattern:
  M-x occur RET (pattern) RET
• Now press e to enter occur-edit-mode to perform interactive edits on those lines only.
• Search and replace.
• Finally, C-cC-c to exit occur-edit-mode, and q to dismiss the occur buffer.

There are third-party libraries to perform similar tricks on earlier versions of Emacs. I believe moccur-edit is one of them, but I've never used it.

edit: Regarding the second part of your question, while I'm not familiar with a more direct way of accomplishing that, we can hack this same method to achieve it:

• M-x occur RET . RET to obtain occur buffer containing all lines
• C-xC-q to make occur buffer writable
• M-x flush-lines RET (pattern) RET to delete matching lines
• C-xC-q to make occur buffer read-only again
• e to invoke occur-edit-mode (and then continue as before...)