10.3.2 Flags for POSIX Regular Expressions
These are the bit flags that you can use in the cflags operand when
compiling a regular expression with
- Treat the pattern as an extended regular expression, rather than as a
basic regular expression.
- Ignore case when matching letters.
- Don't bother storing the contents of the matches-ptr array.
- Treat a newline in string as dividing string into multiple
lines, so that ‘$’ can match before the newline and ‘^’ can
match after. Also, don't permit ‘.’ to match a newline, and don't
permit ‘[^...]’ to match a newline.
Otherwise, newline acts like any other ordinary character.