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, 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 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.
\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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regexp(5) regexp(5)
. 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, 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 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 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 \, e.g. \\.
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.
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regexp(5) regexp(5)
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.
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 /.
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regexp(5) regexp(5)
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.
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 VALUE
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.
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regexp(5) regexp(5)
ERRORS
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');
. . .
if (step(linebuf, expbuf))
succeed;
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