regexp(3) LPC Library Functions regexp(3) NAME regexp() - regular expression handler SYNOPSIS string *regexp( string *lines, string pattern, void | int flag ); DESCRIPTION Typically when presented with an array of lines of text and a regular expression, regexp(3) returns an array containing those lines which match the pattern specified by the regular expression. If the flag (default 0) has bit 2 set, then non-matches will be returned instead of matches. If the flag has bit 1 set, the array returned will be of the form ({ index1 + 1, match1, ..., indexn + 1, matchn }) where index1 is the index of 1st match/non match in the array lines. REGULAR EXPRESSION SYNTAX A regular expression is zero or more _b_r_a_n_c_h_e_s, separated by `|'. It matches anything that matches one of the branches. A branch is zero or more _p_i_e_c_e_s, concatenated. It matches a match for the first, followed by a match for the second, etc. A piece is an _a_t_o_m possibly followed by `*', `+', or `?'. An atom followed by `*' matches a sequence of 0 or more matches of the atom. An atom followed by `+' matches a sequence of 1 or more matches of the atom. An atom followed by `?' matches a match of the atom, or the null string. An atom is a regular expression in parentheses (matching a match for the regular expression), a _r_a_n_g_e (see below), `.' (matching any single character), `^' (matching the null string at the beginning of the input string), `$' (matching the null string at the end of the input string), a `\' fol- lowed by a single character (matching that character), or a single character with no other significance (matching that character). A _r_a_n_g_e is a sequence of characters enclosed in `[]'. It normally matches any single character from the sequence. If the sequence begins with `^', it matches any single charac- ter _n_o_t from the rest of the sequence. If two characters in the sequence are separated by `-', this is shorthand for the full list of ASCII characters between them (e.g. `[0-9]' matches any decimal digit). To include a literal `]' in the sequence, make it the first character (following a possible `^'). To include a literal `-', make it the first or last MudOS Last change: 5 Sep 1994 1 regexp(3) LPC Library Functions regexp(3) character. AMBIGUITY If a regular expression could match two different parts of the input string, it will match the one which begins earli- est. If both begin in the same place but match different lengths, or match the same length in different ways, life gets messier, as follows. In general, the possibilities in a list of branches are con- sidered in left-to-right order, the possibilities for `*', `+', and `?' are considered longest-first, nested constructs are considered from the outermost in, and concatenated con- structs are considered leftmost-first. The match that will be chosen is the one that uses the earliest possibility in the first choice that has to be made. If there is more than one choice, the next will be made in the same manner (earli- est possibility) subject to the decision on the first choice. And so forth. For example, `(ab|a)b*c' could match `abc' in one of two ways. The first choice is between `ab' and `a'; since `ab' is earlier, and does lead to a successful overall match, it is chosen. Since the `b' is already spoken for, the `b*' must match its last possibility-the empty string-since it must respect the earlier choice. In the particular case where no `|'s are present and there is only one `*', `+', or `?', the net effect is that the longest possible match will be chosen. So `ab*', presented with `xabbbby', will match `abbbb'. Note that if `ab*' is tried against `xabyabbbz', it will match `ab' just after `x', due to the begins-earliest rule. (In effect, the deci- sion on where to start the match is the first choice to be made, hence subsequent choices must respect it even if this leads them to less-preferred alternatives.) SEE ALSO sscanf(3), explode(3), strsrch(3), ed(3) MudOS Last change: 5 Sep 1994 2