regexp(3X) regexp(3X)
NAME
compile(), step(), advance() - regular expression compile and match
routines
SYNOPSIS
#define INIT declarations
#define GETC() getc statements
#define PEEKC() peekc statements
#define UNGETC(c) ungetc statements
#define RETURN(pointer) return statements
#define ERROR(val) error statements
#include <regexp.h>
char *compile(
const 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;
extern int circf, sed, nbra;
Remarks
Features documented in this manual entry are obsolescent and may be
removed in a future HP-UX release. Use of regcomp(3C) functions
instead is recommended.
DESCRIPTION
These functions are general-purpose regular expression matching
routines to be used in programs that perform Basic Regular Expression
(see regexp(5)) matching. These functions are defined in <regexp.h>.
The functions step() and advance() do pattern matching given a
character string and a compiled regular expression as input.
compile() takes a Basic Regular Expression as input and produces a
compiled expression that can be used with step() and advance().
The interface to this file is unpleasantly complex. Programs that
include this file must have the following five macros declared before
the #include <regexp.h> statement. These macros are used by the
compile() routine.
GETC() Return the value of the next byte in the regular
expression pattern. Successive calls to GETC() should
Hewlett-Packard Company - 1 - HP-UX Release 10.20: July 1996
regexp(3X) regexp(3X)
return successive bytes of the regular expression.
PEEKC() Return the next byte in the regular expression.
Successive calls to PEEKC() should return the same byte
(which should also be the next byte returned by GETC().
UNGETC(c) Cause the argument c to be returned by the next call to
GETC() (and PEEKC()). No more than one byte of
pushback is ever needed, and this byte is guaranteed to
be the last byte read by GETC(). The value of the
macro UNGETC(c) is always ignored.
RETURN(pointer)
This macro is used on normal exit of the compile()
routine. The value of the argument pointer is a
pointer to the character after the last character of
the compiled regular expression. This is useful to
programs that must manage memory allocation.
ERROR(val) This is the abnormal return from the compile() routine.
The argument val is an error number (see table below
for meanings). This call should never return.
Error Meaning
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.
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 that 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
location where the compiled regular expression will be placed.
Hewlett-Packard Company - 2 - HP-UX Release 10.20: July 1996
regexp(3X) regexp(3X)
The parameter endbuf is one more than the highest address where the
compiled regular expression can 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. For example, in ed(1), this character is usually a /.
Each program that includes this file must have a #define statement for
INIT. This definition is placed right after the declaration for the
function compile() and the opening curly brace {. 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 the example below of the declarations
taken from grep(1).
step() also performs actual regular expression matching in this file.
The call to step is as follows:
step(string, expbuf)
The first parameter to step() 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 that
was obtained by a call to compile().
step() returns non-zero if the given string matches the regular
expression, and zero if the expressions do not match. If there is a
match, two external character pointers are set as a side effect to the
call to step(). The variable set in step() is loc1. This is a
pointer to the first character that matched the regular expression.
The variable loc2, which is set by the function advance(), points to
the character after the last character that matches the regular
expression. Thus, if the regular expression matches the entire line,
loc1 points to the first character of string and loc2 points to the
null at the end of string.
step() uses the external variable circf(), which is set by compile()
if the regular expression begins with ^. If this is set, step() tries
to match the regular expression to the beginning of the string only.
If more than one regular expression is to be compiled before the first
is executed, the value of circf should be saved for each compiled
expression and circf should be set to that saved value before each
call to step().
advance() is called from step() with the same arguments as step().
The purpose of step() is to step through the string argument and call
advance() until advance() returns non-zero, which indicates a match,
Hewlett-Packard Company - 3 - HP-UX Release 10.20: July 1996
regexp(3X) regexp(3X)
or until the end of string is reached. To constrain string to
beginning-of-line in all cases, step() need not be called; simply call
advance().
When advance() encounters a * or \{\} sequence in the regular
expression, it advances its pointer to the string to be matched as far
as possible and recursively calls itself, trying to match the rest of
the string to the rest of the regular expression. As long as there is
no match, advance backs 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() breaks out of the loop that backs up and
returns zero. This is used by ed(1) and sed(1) for substitutions done
globally (not just the first occurrence, but the whole line) so, for
example, expressions such as s/y*//g do not loop forever.
The additional external variables sed and nbra are used for special
purposes.
EXTERNAL INFLUENCES
Locale
The LC_COLLATE category determines the collating sequence used in
compiling and executing regular expressions.
The LC_CTYPE category determines the interpretation of text as single
and/or multi-byte characters, and the characters matched by character
class expressions in regular expressions.
International Code Set Support
Single- and multi-byte character code sets are supported.
EXAMPLES
The following is an example of how the regular expression macros and
calls look from grep(1):
#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();
Hewlett-Packard Company - 4 - HP-UX Release 10.20: July 1996
regexp(3X) regexp(3X)
AUTHOR
regexp() was developed by OSF and HP.
SEE ALSO
grep(1), regcomp(3C), setlocale(3C), regexp(5).
STANDARDS CONFORMANCE
advance(): AES, SVID2, SVID3, XPG2, XPG3, XPG4
compile(): AES, SVID2, SVID3, XPG2, XPG3, XPG4
loc1: AES, SVID2, SVID3, XPG2, XPG3, XPG4
loc2: AES, SVID2, SVID3, XPG2, XPG3, XPG4
locs: AES, SVID2, SVID3, XPG2, XPG3, XPG4
step(): AES, SVID2, SVID3, XPG2, XPG3, XPG4
Hewlett-Packard Company - 5 - HP-UX Release 10.20: July 1996