ES2 MUD LIB :: 東方故事二(ES2) 天朝帝國 mudlib 瀏覽展示
/doc/efuns/regexp
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regexp() - regular expression handler
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string *regexp( string *lines, string pattern, void | int
flag );
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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.
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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 `\'
followed 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
character _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
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it the first or last character.
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If a regular expression could match two different parts of
the input string, it will match the one which begins
earliest. 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
considered in left-to-right order, the possibilities for
`*', `+', and `?' are considered longest-first, nested
constructs are considered from the outermost in, and
concatenated constructs 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 (earliest 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
decision 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.)
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sscanf(3), explode(3), strsrch(3), ed(3)
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