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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 regcomp.

REG_EXTENDED

Treat the pattern as an extended regular expression, rather than as a basic regular expression.

REG_ICASE

Ignore case when matching letters.

REG_NOSUB

Don’t bother storing the contents of the matches-ptr array.

REG_NEWLINE

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.