regex(7) Miscellaneous Information Manual regex(7) regex - POSIX.2 ("RE"s) POSIX.2 : ( egrep(1) POSIX.2 "") ( ed(1) POSIX.2 ""). . POSIX.2 "(!)" POSIX.2 . () (!) (!) '|'. . (!) . . (!) '*' '+' '?' . '*' 0 . '+' 1 . '?' 0 1 . '{' ',' '}'. 0 RE_DUP_MAX (255(!)) . i i . i i . i j i j () . "()" ( ) "()" ( )(!) ( ) '.' ( ) '^' ( ) '$' ( ) '\' "^.[$()|*+?{\" ( ) '\' (!) ( '\' (!)) ( ). '{' (!). '\'. "[]". ( ). '^' . '-' () "[0-9]" ASCII . (!) "a-c-e". . ']' ( '^' ). '-' . '-' "[." ".]" ( ). '[' ( ) '\' . ( ) "[." ".]" . . "ch" "[[.ch.]]*c" "chchcc". "[=" "=]" . ( "[." ".]"). o o "[[=o=]]" "[[=o=]]" "[oo]" . (!) . "[:" ":]" . : alnum digit punct alpha graph space blank lower upper cntrl print xdigit wctype(3). . . . . . . . . "bb*" "abbbc" "(wee|week)(knights|nights)" "weeknights" "(.*).*" "abc" "(a*)*" "bc" . . 'x' "[xX]". "[x]" "[xX]" "[^x]" "[^xX]". (!). 256 POSIX. ("") . '|' '+' '?' . "\{" "\}" '{' '}' . "\(" "\)" '(' ')' . '^' (!) '$' (!) '*' ( '^' ). : '\' d d ( ) "\([bc]\)\1" "bb" "cc" "bc". . POSIX.2 ')' '(' . . . ( "a\(\(b\)*\2\)*d" "abbbd"). . POSIX.2 . " " . regex . grep(1) regex(3) POSIX.2 2.8 ( ). 3 . . : . 6.18 8 2026 regex(7)