How to negate specific word in regex?

Question

I know that I can negate group of chars as in [^bar] but I need a regular expression where negation applies to the specific word - so in my example how do I negate an actual "bar" and not "any chars in bar"?

Answer 1

The following regex will do what you want (as long as negative lookbehinds and lookaheads are supported), matching things properly; the only problem is that it matches individual characters (i.e. each match is a single character rather than all characters between two consecutive "bar"s), possibly resulting in a potential for high overhead if you're working with very long strings.

b(?!ar)|(?<!b)a|a(?!r)|(?<!ba)r|[^bar]

Answer 2

Solution:

^(?!.*STRING1|.*STRING2|.*STRING3).*$

xxxxxx OK

xxxSTRING1xxx KO (is whether it is desired)

xxxSTRING2xxx KO (is whether it is desired)

xxxSTRING3xxx KO (is whether it is desired)

Answer 3

I came across this forum thread while trying to identify a regex for the following English statement:

Given an input string, match everything unless this input string is exactly 'bar'; for example I want to match 'barrier' and 'disbar' as well as 'foo'.

Here's the regex I came up with

^(bar.+|(?!bar).*)$

My English translation of the regex is "match the string if it starts with 'bar' and it has at least one other character, or if the string does not start with 'bar'.

Answer 4

I had a list of file names, and I wanted to exclude certain ones, with this sort of behavior (Ruby):

files = [
  'mydir/states.rb',      # don't match these
  'countries.rb',
  'mydir/states_bkp.rb',  # match these
  'mydir/city_states.rb' 
]
excluded = ['states', 'countries']

# set my_rgx here

result = WankyAPI.filter(files, my_rgx)  # I didn't write WankyAPI...
assert result == ['mydir/city_states.rb', 'mydir/states_bkp.rb']

Here's my solution:

excluded_rgx = excluded.map{|e| e+'\.'}.join('|')
my_rgx = /(^|\/)((?!#{excluded_rgx})[^\.\/]*)\.rb$/

My assumptions for this application:

• The string to be excluded is at the beginning of the input, or immediately following a slash.
• The permitted strings end with .rb.
• Permitted filenames don't have a . character before the .rb.