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This interface is made obsolete by It is available from the compatibility
library, libcompat. The and functions implement regular expressions
and supporting facilities. The function compiles a regular expression
into a structure of type and returns a pointer to it. The space has been
allocated using and may be released by The function matches a against
the compiled regular expression in It returns 1 for success and 0 for
failure, and adjusts the contents of and (see below) accordingly. The
members of a structure include at least the following (not necessarily
in order): char *startp[NSUBEXP]; char *endp[NSUBEXP]; where is defined
(as 10) in the header file. Once a successful has been done using the
each pair describes one substring within the with the pointing to the
first character of the substring and the pointing to the first character
following the substring. The 0th substring is the substring of that matched
the whole regular expression. The others are those substrings that matched
parenthesized expressions within the regular expression, with parenthesized
expressions numbered in left-to-right order of their opening parentheses.
The function copies to making substitutions according to the most recent
performed using Each instance of ‘&’ in is replaced by the substring indicated
by and Each instance of where is a digit, is replaced by the substring
indicated by and To get a literal ‘&’ or into prefix it with ‘\’; to get
a literal ‘\’ preceding ‘&’ or prefix it with another ‘\’. The function is called
whenever an error is detected in or The default writes the string
with a suitable indicator of origin, on the standard error output and invokes
The function can be replaced by the user if other actions are desirable.
A regular expression is zero or more separated
by ‘|’. It matches anything that matches one of the branches. A branch is zero
or more concatenated. It matches a match for the first, followed by a match
for the second, etc. A piece is an 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 (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 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 from the
rest of the sequence. If two characters in the sequence are separated by
‘-’, this is shorthand for the full list of 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 character.
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, 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 presented with ‘xabbbby’, will match ‘abbbb’. Note
that if 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.)
The
function returns for a failure permitting), where failures are syntax
errors, exceeding implementation limits, or applying ‘+’ or ‘*’ to a possibly-null
operand.
Both code and manual page for and were
written at the University of Toronto and appeared in They are intended
to be compatible with the Bell V8 but are not derived from Bell code.
Empty
branches and empty regular expressions are not portable to V8. The restriction
against applying ‘*’ or ‘+’ to a possibly-null operand is an artifact of the
simplistic implementation. Does not support newline-separated branches;
neither does the V8 though. Due to emphasis on compactness and simplicity,
it’s not strikingly fast. It does give special attention to handling simple
cases quickly.
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