regexp(5) regexp(5)
NAME
regexp: compile, step, advance - regular expression compile
and match routines
SYNOPSIS
#define INIT declarations
#define GETC(void) getc code
#define PEEKC(void) peekc code
#define UNGETC(void) ungetc code
#define RETURN(ptr) return code
#define ERROR(val) error code
#include <regexp.h>
char *compile(char *instring, char *expbuf, const char *endbuf, int eof);
int step(const char *string, const char *expbuf);
int advance(const char *string, const char *expbuf);
extern char *loc1, *loc2, *locs;
DESCRIPTION
These functions are general purpose regular expression
matching routines to be used in programs that perform regular
expression matching. These functions are defined by the
regexp.h header file.
The functions step and advance do pattern matching given a
character string and a compiled regular expression as input.
The function compile takes as input a regular expression as
defined below and produces a compiled expression that can be
used with step or advance.
A regular expression specifies a set of character strings. A
member of this set of strings is said to be matched by the
regular expression. Some characters have special meaning when
used in a regular expression; other characters stand for
themselves.
The regular expressions available for use with the regexp
functions are constructed as follows:
Expression Meaning
c the character c where c is not a special
character.
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regexp(5) regexp(5)
\c the character c where c is any character, except a
digit in the range 1-9.
^ the beginning of the line being compared.
$ the end of the line being compared.
. any character in the input.
[s] any character in the set s, where s is a sequence
of characters and/or a range of characters, for
example, [c-c].
[^s] any character not in the set s, where s is defined
as above.
r* zero or more successive occurrences of the regular
expression r. The longest leftmost match is
chosen.
rx the occurrence of regular expression r followed by
the occurrence of regular expression x.
(Concatenation)
r\{m,n\} any number of m through n successive occurrences
of the regular expression r. The regular
expression r\{m\} matches exactly m occurrences;
r\{m,\} matches at least m occurrences.
\(r\) the regular expression r. When \n (where n is a
number greater than zero) appears in a constructed
regular expression, it stands for the regular
expression x where x is the nth regular expression
enclosed in \( and \) that appeared earlier in the
constructed regular expression. For example,
\(r\)x\(y\)z\2 is the concatenation of regular
expressions rxyzy.
Characters that have special meaning except when they appear
within square brackets ([]) or are preceded by \ are: ., *, [,
\. Other special characters, such as $ have special meaning
in more restricted contexts.
The character ^ at the beginning of an expression permits a
successful match only immediately after a newline, and the
character $ at the end of an expression requires a trailing
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regexp(5) regexp(5)
newline.
Two characters have special meaning only when used within
square brackets. The character - denotes a range, [c-c],
unless it is just after the open bracket or before the closing
bracket, [-c] or [c-] in which case it has no special meaning.
When used within brackets, the character ^ has the meaning
complement of if it immediately follows the open bracket
(example: [^c]); elsewhere between brackets (example: [c^]) it
stands for the ordinary character ^.
The special meaning of the \ operator can be escaped only by
preceding it with another \, for example, \\.
Programs must have the following five macros declared before
the #include regexp.h statement. These macros are used by the
compile routine. The macros GETC, PEEKC, and UNGETC operate
on the regular expression given as input to compile.
GETC This macro returns the value of the next
character (byte) in the regular expression
pattern. Successive calls to GETC should
return successive characters of the regular
expression.
PEEKC This macro returns the next character (byte) in
the regular expression. Immediately successive
calls to PEEKC should return the same
character, which should also be the next
character returned by GETC.
UNGETC This macro causes the argument c to be returned
by the next call to GETC and PEEKC. No more
than one character of pushback is ever needed
and this character is guaranteed to be the last
character read by GETC. The return value of
the macro UNGETC(c) is always ignored.
RETURN(ptr) This macro is used on normal exit of the
compile routine. The value of the argument ptr
is a pointer to the character after the last
character of the compiled regular expression.
This is useful to programs which have memory
allocation to manage.
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regexp(5) regexp(5)
ERROR(val) This macro is the abnormal return from the
compile routine. The argument val is an error
number [see ERRORS below for meanings]. This
call should never return.
The syntax of the compile routine is as follows:
compile(instring, expbuf, endbuf, eof)
The first parameter, instring, is never used explicitly by the
compile routine but is useful for programs that pass down
different pointers to input characters. It is sometimes used
in the INIT declaration (see below). Programs which call
functions to input characters or have characters in an
external array can pass down a value of (char *)0 for this
parameter.
The next parameter, expbuf, is a character pointer. It points
to the place where the compiled regular expression will be
placed.
The parameter endbuf is one more than the highest address
where the compiled regular expression may be placed. If the
compiled expression cannot fit in (endbuf-expbuf) bytes, a
call to ERROR(50) is made.
The parameter eof is the character which marks the end of the
regular expression. This character is usually a /.
Each program that includes the regexp.h header file must have
a #define statement for INIT. It is used for dependent
declarations and initializations. Most often it is used to
set a register variable to point to the beginning of the
regular expression so that this register variable can be used
in the declarations for GETC, PEEKC, and UNGETC. Otherwise it
can be used to declare external variables that might be used
by GETC, PEEKC and UNGETC. [See EXAMPLE below.]
The first parameter to the step and advance functions is a
pointer to a string of characters to be checked for a match.
This string should be null terminated.
The second parameter, expbuf, is the compiled regular
expression which was obtained by a call to the function
compile.
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regexp(5) regexp(5)
The function step returns non-zero if some substring of string
matches the regular expression in expbuf and zero if there is
no match. If there is a match, two external character
pointers are set as a side effect to the call to step. The
variable loc1 points to the first character that matched the
regular expression; the variable loc2 points to the character
after the last character that matches the regular expression.
Thus if the regular expression matches the entire input
string, loc1 will point to the first character of string and
loc2 will point to the null at the end of string.
The function advance returns non-zero if the initial substring
of string matches the regular expression in expbuf. If there
is a match, an external character pointer, loc2, is set as a
side effect. The variable loc2 points to the next character
in string after the last character that matched.
When advance encounters a * or \{ \} sequence in the regular
expression, it will advance its pointer to the string to be
matched as far as possible and will recursively call itself
trying to match the rest of the string to the rest of the
regular expression. As long as there is no match, advance
will back up along the string until it finds a match or
reaches the point in the string that initially matched the *
or \{ \}. It is sometimes desirable to stop this backing up
before the initial point in the string is reached. If the
external character pointer locs is equal to the point in the
string at sometime during the backing up process, advance will
break out of the loop that backs up and will return zero.
The external variables circf, sed, and nbra are reserved.
RETURN VALUES
The function compile uses the macro RETURN on success and the
macro ERROR on failure (see above). The functions step and
advance return non-zero on a successful match and zero if
there is no match. Errors are:
11 range endpoint too large.
16 bad number.
25 \ digit out of range.
36 invalid or missing delimiter.
41 no remembered search string.
42 \( \) imbalance.
43 too many \(.
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regexp(5) regexp(5)
44 more than 2 numbers given in \{ \}.
45 } expected after \.
46 first number exceeds second in \{ \}.
49 [ ] imbalance.
50 regular expression overflow.
EXAMPLES
The following is an example of how the regular expression
macros and calls might be defined by an application program:
#define INIT register char *sp = instring;
#define GETC (*sp++)
#define PEEKC (*sp)
#define UNGETC(c) (--sp)
#define RETURN(c) return;
#define ERROR(c) regerr
#include <regexp.h>
. . .
(void) compile(*argv, expbuf, &expbuf[ESIZE],'\0');
. . .
if (step(linebuf, expbuf))
succeed;
REFERENCES
regexpr(3G)
Copyright 1994 Novell, Inc. Page 6