4.4BSD/usr/share/man/cat3/regexp.0
REGEXP(3) BSD Programmer's Manual REGEXP(3)
NNAAMMEE
rreeggccoommpp, rreeggeexxeecc, rreeggssuubb, rreeggeerrrroorr - regular expression handlers
SSYYNNOOPPSSIISS
##iinncclluuddee <<rreeggeexxpp..hh>>
_r_e_g_e_x_p _*
rreeggccoommpp(_c_o_n_s_t _c_h_a_r _*_e_x_p);
_i_n_t
rreeggeexxeecc(_c_o_n_s_t _r_e_g_e_x_p _*_p_r_o_g, _c_o_n_s_t _c_h_a_r _*_s_t_r_i_n_g);
_v_o_i_d
rreeggssuubb(_c_o_n_s_t _r_e_g_e_x_p _*_p_r_o_g, _c_o_n_s_t _c_h_a_r _*_s_o_u_r_c_e, _c_h_a_r _*_d_e_s_t);
DDEESSCCRRIIPPTTIIOONN
This interface is made obsolete by regex(3).
The rreeggccoommpp(), rreeggeexxeecc(), rreeggssuubb(), and rreeggeerrrroorr() functions implement
egrep(1)-style regular expressions and supporting facilities.
The rreeggccoommpp() function compiles a regular expression into a structure of
type regexp, and returns a pointer to it. The space has been allocated
using malloc(3) and may be released by free.
The rreeggeexxeecc() function matches a NUL-terminated _s_t_r_i_n_g against the com-
piled regular expression in _p_r_o_g. It returns 1 for success and 0 for
failure, and adjusts the contents of _p_r_o_g's _s_t_a_r_t_p and _e_n_d_p (see below)
accordingly.
The members of a regexp structure include at least the following (not
necessarily in order):
char *startp[NSUBEXP];
char *endp[NSUBEXP];
where NSUBEXP is defined (as 10) in the header file. Once a successful
rreeggeexxeecc() has been done using the rreeggeexxpp(), each _s_t_a_r_t_p- _e_n_d_p pair de-
scribes one substring within the _s_t_r_i_n_g, with the _s_t_a_r_t_p pointing to the
first character of the substring and the _e_n_d_p pointing to the first char-
acter following the substring. The 0th substring is the substring of
_s_t_r_i_n_g that matched the whole regular expression. The others are those
substrings that matched parenthesized expressions within the regular ex-
pression, with parenthesized expressions numbered in left-to-right order
of their opening parentheses.
The rreeggssuubb() function copies _s_o_u_r_c_e to _d_e_s_t, making substitutions accord-
ing to the most recent rreeggeexxeecc() performed using _p_r_o_g. Each instance of
`&' in _s_o_u_r_c_e is replaced by the substring indicated by _s_t_a_r_t_p[] and
_e_n_d_p[]. Each instance of `\_n', where _n is a digit, is replaced by the
substring indicated by _s_t_a_r_t_p[_n] and _e_n_d_p[_n]. To get a literal `&' or
`\_n' into _d_e_s_t, prefix it with `\'; to get a literal `\' preceding `&' or
`\_n', prefix it with another `\'.
The rreeggeerrrroorr() function is called whenever an error is detected in
rreeggccoommpp(), rreeggeexxeecc(), or rreeggssuubb(). The default rreeggeerrrroorr() writes the
string _m_s_g, with a suitable indicator of origin, on the standard error
output and invokes exit(2). The rreeggeerrrroorr() function can be replaced by
the user if other actions are desirable.
RREEGGUULLAARR EEXXPPRREESSSSIIOONN SSYYNNTTAAXX
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 fol-
lowed 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 char-
acter), `^' (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 match-
es 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 it the first or last character.
AAMMBBIIGGUUIITTYY
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 consid-
ered 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 af-
ter `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 alter-
natives.)
RREETTUURRNN VVAALLUUEESS
The rreeggccoommpp() function returns NULL for a failure (rreeggeerrrroorr() permit-
ting), where failures are syntax errors, exceeding implementation limits,
or applying `+' or `*' to a possibly-null operand.
SSEEEE AALLSSOO
ed(1), ex(1), expr(1), egrep(1), fgrep(1), grep(1), regex(3)
HHIISSTTOORRYY
Both code and manual page for rreeggccoommpp(), rreeggeexxeecc(), rreeggssuubb(), and
rreeggeerrrroorr() were written at the University of Toronto and appeared in
4.3BSD-Tahoe. They are intended to be compatible with the Bell V8
regexp(3), but are not derived from Bell code.
BBUUGGSS
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 egrep's newline-separated branches; neither does the V8
regexp(3), though.
Due to emphasis on compactness and simplicity, it's not strikingly fast.
It does give special attention to handling simple cases quickly.
4.4BSD June 4, 1993 3