问题
I am sooo close. I am trying code a regex expression for Notepad++ to replace a dash with a space, ignoring dashes already with a pre/post space. I realize I could search/replace " - " with "foobarfoo" then search for "-" replacing for " " then converting "foobarfoo" back to " - ", but damnit - I'm trying to learn regex!
Here's my problem:
Adapter - BNC Male to BNC-Female, Right Angle
to
Adapter - BNC Male to BNC Female, Right Angle
(note the disappearing dash in "BNC Female")
The closest I am getting is using this:
/(?:[^( )])\-(?:[^( )])/g
but that results with it finding the single letter ahead, the dash, and the single letter following:
Adapter - BNC Male to BNC-Female, Right Angle
WHY is it selecting the pre/post characters? Is this not:
(?:[^( )]) find anything except a space (as a noncapturing group)...
\- ... that follows with a dash ...
(?:[^( )]) ... and is followed by anything except a space(as a noncapturing group)
I get even closer is I replace the first term with (?=[^( )]) but if I change the third term to (?![^( )]) I'm back to where I started - just selecting the dash in between the two spaces. GRRRR.
More samples here at http://regexr.com/444i2
回答1:
To ignore dashes already with a pre/post space you could use positive lookarounds to assert that what is on the left and on the right are a non whitespace character \S
In the replacement use a space.
(?<=\S)-(?=\S)
Regex demo
回答2:
Use \w(-)\w to replace all hyphens surrounded by alphabetic characters, digits and underscores, or [^ ](-)[^ ] to replace all hyphens surrounded by non-space characters.
Both work fine in my Notepad++ version with all of your examples.
回答3:
The most readable option for Notepad++ is an alternation based regex with a conditional replacement pattern:
Find What: (\s-\s)|-
Replace With: (?1$1: )
The (\s-\s)|- pattern either captures into Group 1 a whitespace, - and a whitespace, or just matches -. If Group 1 matches, its value is pasted back where it was (=this match is skipped), else the - in other contexts is replaced with a space.
See a demo below:
Another option is using nested lookarounds:
Find What: -(?<!\s-(?!=\s))
Replace With: (a space)
The pattern matches:
-- a hyphen(?<!\s-(?!=\s))- this negative lookbehind fails the match if its pattern matches the following pattern immediately to the left of the current location (that is, right after-):\s- a whitespace-- a hyphen (this is necessary to make sure we get to the same place where the lookbehind was triggered)(?!=\s)- the next char is a whitespace (this is a lookahead, it is not possible to make it a simple\sas we cannot let the lookbehind move its pattern position matching, i.e. we can't let it try\s-\sbefore and including-(it would result in a true result).
来源：https://stackoverflow.com/questions/53569626/regex-find-instance-of-dash-but-not-spacedashspace