Re: [PATCH] vi: POSIX backslashes in expand_args

On Tue, 18 Aug 2026 08:54:11 +1000
Morgan via busybox <[email protected]> wrote:

> vi: POSIX backslashes in expand_args

POSIX won't say anything about the way vi should handle \ escapes.
The best you can do is look at how other re-implementations of vi
behave.

	David

> 
> The previous behaviour treated every backslash as escaping a character,
> rather than following POSIX, which only removes backslashes where they
> are escaping a special character.
> 
> And so only one backslash is lost when having a chain of backslashes
> with a percent sign at the end. (plus any shell handling of backslashes
> in unquoted arguments)
> 
> Signed-off-by: Morgan Bartlett <[email protected]>
> 
> diff --git a/editors/vi.c b/editors/vi.c
> index ba607bcfd..d91a4a504 100644
> --- a/editors/vi.c
> +++ b/editors/vi.c
> @@ -2696,7 +2696,9 @@ static char *expand_args(char *args)
>  		} else if (*s == '#') {
>  			replace = alt_filename;
>  		} else {
> -			if (*s == '\\' && s[1] != '\0') {
> +			/* According to POSIX, backslash-escapes are ignored
> unless they
> +			 * escape a special character. It gives an example
> of \\% expanding to \% */
> +			if (*s == '\\' && (s[1] == '%' || s[1] == '#')) {
>  				char *t;
>  				for (t = s; *t; t++)
>  					*t = t[1];
> 
> 
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