REGEXP(5-SVR4) RISC/os Reference Manual REGEXP(5-SVR4)
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, char *endbuf, int eof);
int step(char *string, char *expbuf);
int advance(char *string, char *expbuf);
extern char *loc1, *loc2, *locs;
DESCRIPTION
These functions are general purpose regular expression
matching routines to be used in programs that perform regu-
lar 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 charac-
ter.
\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.
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. any character in the input.
[s] any character in the set s, where s is a
sequence of characters and/or a range of charac-
ters, e.g., [c-c].
[^s] any character not in the set s, where s is
defined as above.
r* zero or more successive occurrences of the regu-
lar 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 con-
structed 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
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 clos-
ing 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 (exam-
ple: [c^]) it stands for the ordinary character ^.
The special meaning of the \ operator can be escaped only by
preceding it with another \, for example, \\.
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Programs must have the following five macros declared before
the #include <regexp.h> statement. These macros are used by
the compile routine. 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 suc-
cessive 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 com-
pile 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.
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 some-
times 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.
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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. Other-
wise 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 com-
pile.
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 char-
acter 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 sub-
string 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
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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.
DIAGNOSTICS
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 illegal or missing delimiter.
41 no remembered search string.
42 \( \) imbalance.
43 too many \(.
44 more than 2 numbers given in \{ \}.
45 } expected after \.
46 first number exceeds second in \{ \}.
49 [ ] imbalance.
50 regular expression overflow.
EXAMPLE
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');
. . .
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if (step(linebuf, expbuf))
succeed;
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