DragonFly On-Line Manual Pages
REGEXP(3) DragonFly Library Functions Manual REGEXP(3)
NAME
regcomp, regexec, regsub, regerror -- regular expression handlers
LIBRARY
Compatibility Library (libcompat, -lcompat)
SYNOPSIS
#include <regexp.h>
regexp *
regcomp(const char *exp);
int
regexec(const regexp *prog, const char *string);
void
regsub(const regexp *prog, const char *source, char *dest);
DESCRIPTION
This interface is made obsolete by regex(3).
The regcomp(), regexec(), regsub(), and regerror() functions implement
egrep(1)-style regular expressions and supporting facilities.
The regcomp() 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(3).
The regexec() function matches a NUL-terminated string against the com-
piled regular expression in prog. It returns 1 for success and 0 for
failure, and adjusts the contents of prog's startp and endp (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
regexec() has been done using the regexp(), each startp- endp pair
describes one substring within the string, with the startp pointing to
the first character of the substring and the endp pointing to the first
character following the substring. The 0th substring is the substring of
string 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 regsub() function copies source to dest, making substitutions accord-
ing to the most recent regexec() performed using prog. Each instance of
`&' in source is replaced by the substring indicated by startp[] and
endp[]. Each instance of `\n', where n is a digit, is replaced by the
substring indicated by startp[n] and endp[n]. To get a literal `&' or
`\n' into dest, prefix it with `\'; to get a literal `\' preceding `&' or
`\n', prefix it with another `\'.
The regerror() function is called whenever an error is detected in
regcomp(), regexec(), or regsub(). The default regerror() writes the
string msg, with a suitable indicator of origin, on the standard error
output and invokes exit(3). The regerror() function can be replaced by
the user if other actions are desirable.
REGULAR EXPRESSION SYNTAX
A regular expression is zero or more branches, separated by `|'. It
matches anything that matches one of the branches.
A branch is zero or more pieces, concatenated. It matches a match for
the first, followed by a match for the second, etc.
A piece is an atom 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 range (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 range 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 not 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.
AMBIGUITY
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
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 alter-
natives.)
RETURN VALUES
The regcomp() function returns NULL for a failure (regerror() permit-
ting), where failures are syntax errors, exceeding implementation limits,
or applying `+' or `*' to a possibly-null operand.
SEE ALSO
ed(1), egrep(1), ex(1), expr(1), fgrep(1), grep(1), regex(3)
HISTORY
Both code and manual page for regcomp(), regexec(), regsub(), and
regerror() 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.
BUGS
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(1)'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.
DragonFly 3.5 June 4, 1993 DragonFly 3.5
regexp(n) Tcl Built-In Commands regexp(n)
______________________________________________________________________________
NAME
regexp - Match a regular expression against a string
SYNOPSIS
regexp ?switches? exp string ?matchVar? ?subMatchVar subMatchVar ...?
______________________________________________________________________________
DESCRIPTION
Determines whether the regular expression exp matches part or all of
string and returns 1 if it does, 0 if it does not, unless -inline is
specified (see below). (Regular expression matching is described in
the re_syntax reference page.)
If additional arguments are specified after string then they are
treated as the names of variables in which to return information about
which part(s) of string matched exp. MatchVar will be set to the range
of string that matched all of exp. The first subMatchVar will contain
the characters in string that matched the leftmost parenthesized
subexpression within exp, the next subMatchVar will contain the
characters that matched the next parenthesized subexpression to the
right in exp, and so on.
If the initial arguments to regexp start with - then they are treated
as switches. The following switches are currently supported:
-about Instead of attempting to match the regular expression,
returns a list containing information about the regular
expression. The first element of the list is a
subexpression count. The second element is a list of
property names that describe various attributes of the
regular expression. This switch is primarily intended
for debugging purposes.
-expanded Enables use of the expanded regular expression syntax
where whitespace and comments are ignored. This is the
same as specifying the (?x) embedded option (see the
re_syntax manual page).
-indices Changes what is stored in the matchVar and subMatchVars.
Instead of storing the matching characters from string,
each variable will contain a list of two decimal strings
giving the indices in string of the first and last
characters in the matching range of characters.
-line Enables newline-sensitive matching. By default, newline
is a completely ordinary character with no special
meaning. With this flag, "[^" bracket expressions and
"." never match newline, "^" matches an empty string
after any newline in addition to its normal function,
and "$" matches an empty string before any newline in
addition to its normal function. This flag is
equivalent to specifying both -linestop and -lineanchor,
or the (?n) embedded option (see the re_syntax manual
page).
-linestop Changes the behavior of "[^" bracket expressions and "."
so that they stop at newlines. This is the same as
specifying the (?p) embedded option (see the re_syntax
manual page).
-lineanchor Changes the behavior of "^" and "$" (the "anchors") so
they match the beginning and end of a line respectively.
This is the same as specifying the (?w) embedded option
(see the re_syntax manual page).
-nocase Causes upper-case characters in string to be treated as
lower case during the matching process.
-all Causes the regular expression to be matched as many
times as possible in the string, returning the total
number of matches found. If this is specified with
match variables, they will contain information for the
last match only.
-inline Causes the command to return, as a list, the data that
would otherwise be placed in match variables. When
using -inline, match variables may not be specified. If
used with -all, the list will be concatenated at each
iteration, such that a flat list is always returned.
For each match iteration, the command will append the
overall match data, plus one element for each
subexpression in the regular expression. Examples are:
regexp -inline -- {\w(\w)} " inlined "
-> in n
regexp -all -inline -- {\w(\w)} " inlined "
-> in n li i ne e
-start index Specifies a character index offset into the string to
start matching the regular expression at. The index
value is interpreted in the same manner as the index
argument to string index. When using this switch, "^"
will not match the beginning of the line, and \A will
still match the start of the string at index. If
-indices is specified, the indices will be indexed
starting from the absolute beginning of the input
string. index will be constrained to the bounds of the
input string.
-- Marks the end of switches. The argument following this
one will be treated as exp even if it starts with a -.
If there are more subMatchVars than parenthesized subexpressions within
exp, or if a particular subexpression in exp does not match the string
(e.g. because it was in a portion of the expression that was not
matched), then the corresponding subMatchVar will be set to "-1 -1" if
-indices has been specified or to an empty string otherwise.
EXAMPLES
Find the first occurrence of a word starting with foo in a string that
is not actually an instance of foobar, and get the letters following it
up to the end of the word into a variable:
regexp {\mfoo(?!bar\M)(\w*)} $string -> restOfWord
Note that the whole matched substring has been placed in the variable
"->", which is a name chosen to look nice given that we are not
actually interested in its contents.
Find the index of the word badger (in any case) within a string and
store that in the variable location:
regexp -indices {(?i)\mbadger\M} $string location
This could also be written as a basic regular expression (as opposed to
using the default syntax of advanced regular expressions) match by
prefixing the expression with a suitable flag:
regexp -indices {(?ib)\<badger\>} $string location
This counts the number of octal digits in a string:
regexp -all {[0-7]} $string
This lists all words (consisting of all sequences of non-whitespace
characters) in a string, and is useful as a more powerful version of
the split command:
regexp -all -inline {\S+} $string
SEE ALSO
re_syntax(n), regsub(n), string(n)
KEYWORDS
match, parsing, pattern, regular expression, splitting, string
Tcl 8.3 regexp(n)