What do `?i` and `?-i` in regex mean?

by

(?i) starts case-insensitive mode

(?-i) turns off case-insensitive mode

More information at the “Turning Modes On and Off for Only Part of The Regular Expression” section of this page:

Modern regex flavors allow you to apply modifiers to only part of the
regular expression. If you insert the modifier (?ism) in the middle of
the regex, the modifier only applies to the part of the regex to the
right of the modifier. You can turn off modes by preceding them with a
minus sign. All modes after the minus sign will be turned off. E.g.
(?i-sm) turns on case insensitivity, and turns off both single-line
mode and multi-line mode.

Not all regex flavors support this. JavaScript and Python apply all
mode modifiers to the entire regular expression. They don’t support
the (?-ismx) syntax, since turning off an option is pointless when
mode modifiers apply to the whole regular expressions. All options are
off by default.

You can quickly test how the regex flavor you’re using handles mode
modifiers. The regex (?i)te(?-i)st should match test and TEst, but not
teST or TEST.

More Related Contents:

  1. Write regular expressions [closed]
  2. Get all three digit numbers from array and store in new array [closed]
  3. /^a-eg-h/.match(‘f’) gives null in Ruby
  4. Regex to match Date
  5. Difference between \A \z and ^ $ in Ruby regular expressions
  6. How to match all occurrences of a regex
  7. Ruby regular expression using variable name
  8. How do I get the match data for all occurrences of a Ruby regular expression in a string?
  9. How do I remove emoji from string
  10. Weird backslash substitution in Ruby
  11. Valid email address regular expression? [duplicate]
  12. Extract a substring from a string in Ruby using a regular expression
  13. Ruby Regular expression to match a url [duplicate]
  14. How to match all occurrences of a regular expression in Ruby
  15. Regex to split BBCode into pieces
  16. Confusion with Atomic Grouping – how it differs from the Grouping in regular expression of Ruby?
  17. Ruby Email validation with regex
  18. What is a regex to match a string NOT at the end of a line?
  19. Match a string against multiple patterns
  20. Matching balanced parenthesis in Ruby using recursive regular expressions like perl
  21. Interpolating a string into a regex
  22. Ruby: filter array by regex?
  23. How to use double brackets in a regular expression?
  24. How to match something with regex that is not between two special characters?
  25. Ruby: String Comparison Issues
  26. Ruby 2.0.0p0 IRB warning: “DL is deprecated, please use Fiddle”
  27. What exactly is `&:capitalize` in Ruby?
  28. In Ruby, is there an Array method that combines ‘select’ and ‘map’?
  29. Ruby: Installing rmagick on Ubuntu
  30. Better ruby markdown interpreter?

Leave a Comment