How to cancel the default in replace-string?

Question

When I use replace-string for the first time, it asks me for the string to replace and string to replace with. When running it again, it uses the previous values as default:

Replace string (default a -> b):

I want to replace an empty string now. I can't just press Enter, though, as that would confirm the default. Is there a way how to replace the empty string after having previously replaced something else?

When asked for the first time without default, just pressing Enter works.

Note: I know there are other ways how to get the thing done. My question is how to enter an empty string when there's a default.

Answer 1

Search regexp \(\) is the exact same as hitting RET when trying to specify an empty string for searching.

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As a quick test, using both \(\) and RET resulted in 833 search hits for this random text block generated using a random text generator.

abc def ghi jkl mno pqrs tuv wxyz ABC DEF GHI JKL MNO PQRS TUV WXYZ ! "§ $%& /() =? * '<>

|; ²³~ @`´ ©«» ¤¼× {} abc def ghi jkl mno pqrs tuv wxyz ABC DEF GHI JKL MNO PQRS TUV WXYZ ! "§ $%& /() =? * '<>

|; ²³~ @`´ ©«» ¤¼× {} abc def ghi jkl mno pqrs tuv wxyz ABC DEF GHI JKL MNO PQRS TUV WXYZ ! "§ $%& /() =? * '<>

|; ²³~ @`´ ©«» ¤¼× {} abc def ghi jkl mno pqrs tuv wxyz ABC DEF GHI JKL MNO PQRS TUV WXYZ ! "§ $%& /() =? * '<> |; ²³~ @`´ ©«» ¤¼× {} abc def ghi jkl mno pqrs tuv wxyz ABC DEF GHI JKL MNO PQRS TUV WXYZ !

"§ $%& /() =? * '<> |; ²³~ @`´ ©«» ¤¼× {} abc def ghi jkl mno pqrs tuv wxyz ABC DEF GHI JKL MNO PQRS TUV WXYZ ! "§ $%& /() =? * '<> |; ²³~ @`´ ©«» ¤¼× {} abc def ghi jkl mno pqrs tuv wxyz ABC DEF GHI JKL MNO PQRS TUV WXYZ ! "§ $%& /() =? * '<> |; ²³~ @`´ ©«» ¤¼× {}abc def ghi jkl mno pqrs tuv wxyz ABC DEF GHI

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But based on your comment:

The input contains digits, I need to separate them by spaces.

using \([[:digit:]]\) as zck states in his answer would be a more efficient search regexp.

Answer 2

This isn't an answer to the exact question you asked, but it does solve your problem.

You can use replace-regexp, with the search regexp as \([[:digit:]]\) and \1 as replacement (Note that there's a space after \1).

The regexp captures a single digit (the character class [:digit:]). The replacement is the group matched in the regexp followed by a space.

Answer 3

I'm not sure this feature existed back in 2016, but nowadays you can press Up when prompted for the replace string, it shows the string a → b where you can delete the a to replace the empty string.

Answer 4

It is not the replace string that makes troubles. It is always the same search string one cannot change!

However, the correct remedy is not the string shown in my previous post, the insert should read instead:

(custom-set-variables' (query-replace-from-to-separator nil) )

Sorry for the confusion ...

Answer 5

After inserting the line

'(query-replace-from-to-separator nil)

into the section (custom-set-variables ... ) of my .gnu-emacs-custom file, the unwanted default search-string behavior disappeared.