Regex match certain string and ignore if it starts with some pattern

Question

I have a following regular expression that I use in C# code that tries to match save some followed by some word and delete some followed by some word in a file.

\\bsave\\ssome\\b\\s[^\\s]+|\\bdelete\\ssome\\b\\s[^\\s]+

This works as expected. Now, I wanted to exclude those from the match that has a pattern like - save some and - delete some .

I tried using the following but it didn't work. In the expression below I just used the expression to ignore - save some Appreciate any help. (?!-\\s\\bsave\\ssome\\b\\s[^\\s])(\\bsave\\ssome\\b\\s[^\\s]+|\\bdelete\\ssome\\b\\s[^\\s]+)

The demo is here

Answer 1

You need to use a negative look-behind and group the pattern:

(?<!-\p{Zs}*)(?:\bsave\ssome\b\s[^\s]+|\bdelete\ssome\b\s[^\s]+)
^^^^^^^^^^^^  ^                                                ^  

See regex demo

The (?<!-\\p{Zs}*) lookbehind fails a match if the save/delete some is preceded with - followed by zero or more spaces (use + if there must be at least one). I used \\p{Zs} to only match horizontal whitespace. If you want to match newlines, use \\s .

A contracted regex version:

(?<!-\s*)\b(save|delete)\ssome\b\s\S+

Use the Explicit Capture flag with it . Since \\ssome\\b\\s\\S+ is common for both alternatives, you can move the end of the group to just include save and delete .

C#:

var rx = @"(?<!-\s*)\b(save|delete)\ssome\b\s\S+";