diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 46 |
1 files changed, 35 insertions, 11 deletions
@@ -643,17 +643,21 @@ If RE is a regular expression, then so is (RE). The contents of parentheses denote one regular expression unit, so that for instance in (RE)*, the * operator applies to the entire parenthesized group. .IP (RE)? -optionally matches the preceding regular expression (RE). +optionally match the preceding regular expression (RE). .IP (RE)+ -matches the preceding expression one or more times. +match the preceding expression one or more times. .IP (RE)* -matches the preceding expression zero or more times. +match the preceding expression zero or more times. +.IP ~(RE) +match the complement of the preceding expression; i.e. match +those texts that (RE) does not match. .IP (RE1)(RE2) Two consecutive regular expressions denote catenation: the left expression must match, and then the right. - .IP (RE1)|(RE2) -matches either the expression RE1 or RE2. +match either the expression RE1 or RE2. +.IP (RE1)&(RE2) +match both the expression RE1 and RE2 simultaneously. .PP Any of the special characters, including the delimiting /, can be escaped with @@ -674,14 +678,34 @@ The postfix operators ?, + and * have the second highest precedence, and associate left to right, so that in A+?*, the * applies to A+?, and the ? applies to A+. -Catenation is on the next lower precedence rung, so that AB? means "match A, -and then optionally B" not "match A and B, as one optional unit". The latter -must be written (AB)? using parentheses to override precedence. +The unary complement operator has the next lower precedence, so +that ~A* means the ~(A*): "match the all text that is not matched by zero +or more repetitions of A", not "match zero or more times the text +not matched by A". + +Catenation is on the next lower precedence rung, so that AB? means A(B?), or +"match A, and then optionally B", not "match A and B, as one optional +unit". The latter must be written (AB)? using parentheses to override +precedence. + +The precedence of conjunction (&) is lower than catenation, but not as low as +that of disjunction, thus AB The disjunction operator | has the lowest precedence, lower than catenation. -Thus abc|def means "match abc, or match def". The meaning "match ab, -then c or d, then ef" must be expressed as ab(c|d)ef, or using -a character class: ab[cd]ef. +Thus ABC|DEF means "match ABC, or match DEF". The meaning "match AB, +then C or D, then EF" must be expressed as AB(C|D)EF, or using +a character class: AB[CD]EF. + +The regular expression + + ABC*&~DEF+|Z + +Is parsed as if it were grouped with parentheses like this: + + ((AB(C*))&(~(DE(F+))))|Z + +The main constituent is the | operator, whose left side is an & expression, +et cetera. In .b txr, |