M_regex Module

  M_regex(3fm) - [M_regex] Fortran interface to POSIX 1003.2 regular
  expression library using ISO_C_BINDING.

  use M_regex, only : regcomp(3f), regexec(3f), regerror(3f), regfree(3f)
  use M_regex, only : regmatch(3f), regsub(3f)

These routines interface with the C implementation of IEEE Std 1003.2
( POSIX.2 ) RE (Regular Expressions).

o The regcomp(3c) function compiles a RE string into an internal form
o regexec(3c) matches that internal form against a string and reports
  results
o regerror(3c) transforms error codes from either into human-readable
  messages
o and regfree(3c) frees any dynamically-allocated storage used by
  the internal form of an RE.

The Fortran interface is composed of wrapper routines that call the C
library, plus some extensions (ie. regmatch(3f), regsub(3f)). See the
C documentation for further details about implementation, performance,
and limitations.

The following constructs are recognized in a ERE (Extended Regular
Expression):

 .     Matches any character except newline.
 *     (postfix) Matches the preceding expression zero, one or several times
 +     (postfix) Matches the preceding expression one or several times
 ?     (postfix) Matches the preceding expression once or not at all
 [..]  Character set. Ranges are denoted with - , as in [a-z] .
       An initial ^ , as in [^0-9] , complements the set. To
       include a ] character in a set, make it the first character
       of the set. To include a - character in a set, make it
       the first or the last character of the set.

 ^        Matches at beginning of line: either at the beginning
          of the matched string, or just after a '\n' character.
 $        Matches at end of line: either at the end of the matched
          string, or just before a '\n' character.
 |        (infix) Alternative between two expressions.
 (..)     Grouping and naming of the enclosed expression.
 \1       The text matched by the first \(...\) expression (
          \2 for the second expression, and so on up to \9 ).
 \b       Matches word boundaries.
 \        Quotes special characters. The special characters are $^\.*+?[] .

Regular expressions ( REs ), as defined in IEEE Std 1003.2
( POSIX.2 ), come in two forms: modern REs (roughly those of
egrep(1); 1003.2 calls these extended REs or ERE) and obsolete REs
(roughly those of ed(1); 1003.2 basic REs or BRE). BRE mostly
exist for backward compatibility in some old programs; they will be
discussed at the end. IEEE Std 1003.2 ( POSIX.2 ) leaves some
aspects of RE syntax and semantics open; decisions on
these aspects mean that conforming implementations of IEEE Std 1003.2
( POSIX.2 ) may not be completely compatible.

A (modern) RE is one or more non-empty branches, separated by |.
It matches anything that matches one of the branches.

A branch is one 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 a single * , + , ? ,
or bound. An atom followed 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 sequence of 0 or 1 matches of the atom.

A bound is { followed by an unsigned decimal integer, possibly
followed by , possibly followed by another unsigned decimal
integer, always followed by } . The integers must lie between
0 and RE_DUP_MAX (255 ) inclusive, and if there are two of them,
the first may not exceed the second. An atom followed by a bound
containing one integer i and no comma matches a sequence of exactly
i matches of the atom. An atom followed by a bound containing one
integer i and a comma matches a sequence of i or more matches of the
atom. An atom followed by a bound containing two integers i and j
matches a sequence of i through j (inclusive) matches of the atom.

An atom is a regular expression enclosed in () (matching a match
for the regular expression), an empty set of () (matching the null
string) , a bracket expression (see below), . (matching any
single character), ^ (matching the null string at the beginning
of a line), $ (matching the null string at the end of a line), a
\\ followed by one of the characters ^.[$()|*+?{\ (matching
that character taken as an ordinary character), a \ followed
by any other character (matching that character taken as an ordinary
character, as if the \ had not been present ), or a single
character with no other significance (matching that character). A {
followed by a character other than a digit is an ordinary character,
not the beginning of a bound . It is illegal to end an RE with
\ .

A bracket expression is a list of characters enclosed in []
. It normally matches any single character from the list (but see
below). If the list begins with ^ , it matches any single
character (but see below) not from the rest of the list. If two
characters in the list are separated by - , this is shorthand
for the full range of characters between those two (inclusive) in the
collating sequence, e.g. [0-9] in ASCII matches any decimal
digit. It is illegal for two ranges to share an endpoint, e.g.
a-c-e . Ranges are very collating-sequence-dependent, and portable
programs should avoid relying on them.

To include a literal ] in the list, make it the first character
(following a possible ^ ). To include a literal - , make
it the first or last character, or the second endpoint of a range. To
use a literal - as the first endpoint of a range, enclose it in
[. and .] to make it a collating element (see below). With
the exception of these and some combinations using [ (see
next paragraphs), all other special characters, including \ ,
lose their special significance within a bracket expression.

Within a bracket expression, a collating element (a character,
a multi-character sequence that collates as if it were a single
character, or a collating-sequence name for either) enclosed in
[. and .] stands for the sequence of characters of that
collating element. The sequence is a single element of the bracket
expression's list. A bracket expression containing a multi-character
collating element can thus match more than one character, e.g. if the
collating sequence includes a ch collating element, then the RE
[[.ch.]]*c matches the first five characters of chchcc .

Within a bracket expression, a collating element enclosed in [=
and =] is an equivalence class, standing for the sequences of
characters of all collating elements equivalent to that one, including
itself. (If there are no other equivalent collating elements, the
treatment is as if the enclosing delimiters were [. and .]
.) For example, if x and y are the members of an equivalence
class, then [[=x=]] , [[=y=]] , and [xy] are all
synonymous. An equivalence class may not be an endpoint of a range.

Within a bracket expression, the name of a character class enclosed in
[: and :] stands for the list of all characters belonging
to that class. Standard character class names are:

      alnum    digit    punct
      alpha    graph    space
      blank    lower    upper
      cntrl    print    xdigit

These stand for the character classes defined in ctype(3). A locale
may provide others. A character class may not be used as an endpoint
of a range.

A bracketed expression like [[:class:]] can be used to match a single
character that belongs to a character class. The reverse, matching
any character that does not belong to a specific class, the negation
operator of bracket expressions may be used: [^[:class:]] .

There are two special cases of bracket expressions: the bracket
expressions [[:<:]] and [[:>:]] match the null string at the beginning
and end of a word respectively. A word is defined as a sequence of word
characters which is neither preceded nor followed by word characters. A
word character is an alnum character (as defined by ctype(3)) or an
underscore. This is an extension, compatible with but not specified
by IEEE Std 1003.2 ( POSIX.2 ), and should be used with caution in
software intended to be portable to other systems.

In the event that an RE could match more than one substring of a given
string, the RE matches the one starting earliest in the string. If the RE
could match more than one substring starting at that point, it matches
the longest. Subexpressions also match the longest possible substrings,
subject to the constraint that the whole match be as long as possible,
with subexpressions starting earlier in the RE taking priority over
ones starting later. Note that higher-level subexpressions thus take
priority over their lower-level component subexpressions.

Match lengths are measured in characters, not collating elements. A
null string is considered longer than no match at all. For example, bb*
matches the three middle characters of abbbc , (wee|week)(knights|nights)
matches all ten characters of weeknights, when (.*).* is matched against
abc the parenthesized subexpression matches all three characters, and
when (a*)* is matched against bc both the whole RE and the parenthesized
subexpression match the null string.

If case-independent matching is specified, the effect is much as if all
case distinctions had vanished from the alphabet. When an alphabetic
that exists in multiple cases appears as an ordinary character outside
a bracket expression, it is effectively transformed into a bracket
expression containing both cases, e.g. x becomes [xX] . When it appears
inside a bracket expression, all case counterparts of it are added
to the bracket expression, so that (e.g.) [x] becomes [xX] and [^x]
becomes [^xX] .

No particular limit is imposed on the length of REs . Programs intended
to be portable should not employ REs longer than 256 bytes, as an
implementation can refuse to accept such REs and remain POSIX-compliant.

Obsolete ( basic ) regular expressions differ in several respects. | is
an ordinary character and there is no equivalent for its functionality. +
and ? are ordinary characters, and their functionality can be expressed
using bounds ( {1,} or {0,1} respectively). Also note that x+ in modern,
REs is equivalent to xx* . The delimiters for bounds are \{ and \}
with { and } by themselves ordinary characters. The parentheses for
nested subexpressions are \( and \) , with ( and ) by themselves ordinary
characters. ^ is an ordinary character except at the beginning of the
RE or the beginning of a parenthesized subexpression, $ is an ordinary
character except at the end of the RE or the end of a parenthesized
subexpression, and * is an ordinary character if it appears at the
beginning of the RE or the beginning of a parenthesized subexpression
(after a possible leading ^ ). Finally, there is one new type of atom, a
back reference: \ followed by a non-zero decimal digit d matches the same
sequence of characters matched by the dth parenthesized subexpression
(numbering subexpressions by the positions of their opening parentheses,
left to right), so that (e.g.) \([bc]\)\1 matches bb or cc but not bc .

Regex is defined as an API using C headers. It does not define the
exact value of flag tokens, just the names. It also uses an opaque
data structure and a declared numeric type for the match array.
Therefore, the code must either be generated for each target
platform, or it must use wrapper functions written in C.

Fortran wrapper functions are also required to present a normal
Fortran API, and to not require C conversions by the caller.

The interface here is not strictly correct, because it does not
explicitly convert Fortran strings to the C character kind.
Fortran only supports conversion of string kinds by assignment,
or by a rather slow internal WRITE. For now, the easiest approach
is to assume that C and Fortran default character kinds are the
same. This is generally true, but UTF-8 strings are likely to
cause problems.

By default, the NUL-terminated string pointed to by string is
considered to be the text of an entire line, minus any terminating
newline. The eflags argument is the bitwise OR of zero or more of
the following flags:

REG_NOTBOL    The first character of the string is not the beginning
              of a line, so the ^ anchor should not match before
              it. This does not affect the behavior of newlines
              under REG_NEWLINE.

REG_NOTEOL    The NUL terminating the string does not end a line,
              so the $ anchor should not match before it. This does
              not affect the behavior of newlines under REG_NEWLINE.

REG_STARTEND  The string is considered to start at string +
              pmatch[0].rm_so and to have a terminating NUL located at string
              + pmatch[0].rm_eo (there need not actually be a NUL
              at that location), regardless of the value of nmatch.
              See below for the definition of pmatch and nmatch. This
              is an extension, compatible with but not specified by
              IEEE Std 1003.2 ( POSIX.2 ), and should be used with
              caution in software intended to be portable to other
              systems. Note that a non-zero rm_so does not imply
              REG_NOTBOL; REG_STARTEND affects only the location of
              the string, not how it is matched.

If REG_NOSUB was specified in the compilation of the RE, or if nmatch
is 0, regexec() ignores the pmatch argument (but see below for the
case where REG_STARTEND is specified). Otherwise, pmatch points to
an array of nmatch structures of type regmatch_t. Such a structure
has at least the members rm_so and rm_eo, both of type regoff_t (a
signed arithmetic type at least as large as an off_t and a ssize_t),
containing respectively the offset of the first character of a
substring and the offset of the first character after the end of
the substring. Offsets are measured from the beginning of the string
argument given to regexec(). An empty substring is denoted by equal
offsets, both indicating the character following the empty substring.

The 0th member of the pmatch array is filled in to indicate what
substring of string was matched by the entire RE. Remaining members
report what substring was matched by parenthesized subexpressions
within the RE; member i reports subexpression i, with subexpressions
counted (starting at 1) by the order of their opening parentheses in
the RE, left to right. Unused entries in the array (corresponding
either to subexpressions that did not participate in the match at
all, or to subexpressions that do not exist in the RE (that is, i >
preg->re_nsub)) have both rm_so and rm_eo set to -1. If a subexpression
participated in the match several times, the reported substring
is the last one it matched. (Note, as an example in particular ,
that when the RE (b*)+ matches bbb , the parenthesized
subexpression matches each of the three b's and then an infinite
number of empty strings following the last b , so the reported
substring is one of the empties.)

If REG_STARTEND is specified, pmatch must point to at least one
regmatch_t (even if nmatch is 0 or REG_NOSUB was specified), to hold
the input offsets for REG_STARTEND. Use for output is still entirely
controlled by nmatch; if nmatch is 0 or REG_NOSUB was specified,
the value of pmatch[0] will not be changed by a successful regexec().

The regerror() function maps a non-zero errcode from either
regcomp() or regexec() to a human-readable, printable message.
If preg is non-NULL, the error code should have arisen from use of
the regex_t pointed to by preg, and if the error code came from
regcomp(), it should have been the result from the most recent
regcomp() using that regex_t. The (regerror() may be able to
supply a more detailed message using information from the regex_t.)
The regerror() function places the NUL-terminated message into the
buffer pointed to by errbuf, limiting the length (including the NUL)
to at most errbuf_size bytes. If the whole message will not fit,
as much of it as will fit before the terminating NUL is supplied.
In any case, the returned value is the size of buffer needed to hold
the whole message (including terminating NUL). If errbuf_size is 0,
errbuf is ignored but the return value is still correct.

The regfree() function frees any dynamically-allocated storage
associated with the compiled RE pointed to by preg. The remaining
regex_t is no longer a valid compiled RE and the effect of supplying
it to regexec() or regerror() is undefined.

None of these functions references global variables except for
tables of constants; all are safe for use from multiple threads if
the arguments are safe.

RE_DUP_MAX, the limit on repetition counts in bounded repetitions,
is 255.

A repetition operator ( ? , * , + , or bounds) cannot
follow another repetition operator. A repetition operator cannot
begin an expression or subexpression or follow ^ or | .

| cannot appear first or last in a (sub)expression or after
another | , i.e., an operand of | cannot be an empty sub
expression. An empty parenthesized subexpression, () , is legal
and matches an empty (sub)string. An empty string is not a legal RE.

A { followed by a digit is considered the beginning of bounds for
a bounded repetition, which must then follow the syntax for bounds. A
{ not followed by a digit is considered an ordinary character.

^ and $ beginning and ending subexpressions in obsolete
( basic ) REs are anchors, not ordinary characters.

The test program test_suite_M_regex may be run via "fpm test"
or when M_regex(3f) is built as part of the GPF (General Purpose
Fortran library) but requires the test framework in GPF so it
cannot be run stand-alone.

Regular Expression Notation, IEEE Std, 1003.2, section 2.8.

grep(1), re_format(7), regex(3)

These routines implement IEEE Std 1003.2 ("POSIX.2") regular expressions ("RE"s); see re_format(7).

IEEE Std 1003.2 (POSIX.2), sections 2.8 (Regular Expression Notation) and B.5 (C Binding for Regular Expression Matching).

 regcomp (3p)  - regular expression matching
 regex (3)     - regular-expression library
 regex (7)     - POSIX 1003.2 regular expressions
 regex.h (0p)  - regular expression matching types
 regexp (n)    - Match a regular expression against a string
 regsub (n)    - Perform substitutions based on regular expression pattern matching