The Ruby Way: Solutions and Techniques in Ruby Programming, Second Edition

3.11. Using Embedded Options

The common way to specify options for a regex is to use a trailing option (such as i or m). But what if we want an option to apply only to part of a regular expression?

We can turn options on and off with a special notation. Within parentheses, a question mark followed by one or more options “turns on” those options for the remainder of the regular expression. A minus sign preceding one or more options “turns off” those options:

/abc(?i)def/         # Will match abcdef, abcDEF, abcDef, ...
                     #   but not ABCdef
/ab(?i)cd(?-i)ef/    # Will match abcdef, abCDef, abcDef, ...
                     #   but not ABcdef or abcdEF
/(?imx).*/           # Same as /.*/imx
/abc(?i-m).*/m       # For last part of regex, turn on case
                     #   sensitivity, turn off multiline

If we want, we ...