zrex(3)
=======

NAME
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zrex - work with regular expressions

SYNOPSIS
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//  Constructor. Optionally, sets an expression against which we can match
//  text and capture hits. If there is an error in the expression, reports
//  zrex_valid() as false and provides the error in zrex_strerror(). If you
//  set a pattern, you can call zrex_matches() to test it against text.
CZMQ_EXPORT zrex_t *
    zrex_new (const char *expression);

//  Destructor
CZMQ_EXPORT void
    zrex_destroy (zrex_t **self_p);

//  Return true if the expression was valid and compiled without errors.
CZMQ_EXPORT bool
    zrex_valid (zrex_t *self);

//  Return the error message generated during compilation of the expression.
CZMQ_EXPORT const char *
    zrex_strerror (zrex_t *self);

//  Returns true if the text matches the previously compiled expression.
//  Use this method to compare one expression against many strings.
CZMQ_EXPORT bool
    zrex_matches (zrex_t *self, const char *text);

//  Returns true if the text matches the supplied expression. Use this
//  method to compare one string against several expressions.
CZMQ_EXPORT bool
    zrex_eq (zrex_t *self, const char *text, const char *expression);

//  Returns number of hits from last zrex_matches or zrex_eq. If the text
//  matched, returns 1 plus the number of capture groups. If the text did
//  not match, returns zero. To retrieve individual capture groups, call
//  zrex_hit ().
CZMQ_EXPORT int
    zrex_hits (zrex_t *self);

//  Returns the Nth capture group from the last expression match, where
//  N is 0 to the value returned by zrex_hits(). Capture group 0 is the
//  whole matching string. Sequence 1 is the first capture group, if any,
//  and so on.
CZMQ_EXPORT const char *
    zrex_hit (zrex_t *self, uint index);

//  Fetches hits into string variables provided by caller; this makes for
//  nicer code than accessing hits by index. Caller should not modify nor
//  free the returned values. Returns number of strings returned. This
//  method starts at hit 1, i.e. first capture group, as hit 0 is always
//  the original matched string.
CZMQ_EXPORT int
    zrex_fetch (zrex_t *self, const char **string_p, ...);

//  Self test of this class
CZMQ_EXPORT void
    zrex_test (bool verbose);
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DESCRIPTION
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Wraps a very simple regular expression library (SLRE) as a CZMQ class.
Supports this syntax:

    ^               Match beginning of a buffer
    $               Match end of a buffer
    ()              Grouping and substring capturing
    [...]           Match any character from set
    [^...]          Match any character but ones from set
    .               Match any character
    \s              Match whitespace
    \S              Match non-whitespace
    \d              Match decimal digit
    \D              Match non decimal digit
    \a              Match alphabetic character
    \A              Match non-alphabetic character
    \w              Match alphanumeric character
    \W              Match non-alphanumeric character
    \r              Match carriage return
    \n              Match newline
    +               Match one or more times (greedy)
    +?              Match one or more times (non-greedy)
    *               Match zero or more times (greedy)
    *?              Match zero or more times (non-greedy)
    ?               Match zero or once
    \xDD            Match byte with hex value 0xDD
    \meta           Match one of the meta character: ^$().[*+?\

Please add @discuss section in ../src/zrex.c.

EXAMPLE
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.From zrex_test method
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//  This shows the pattern of matching many lines to a single pattern
zrex_t *rex = zrex_new ("\\d+-\\d+-\\d+");
assert (rex);
assert (zrex_valid (rex));
bool matches = zrex_matches (rex, "123-456-789");
assert (matches);
assert (zrex_hits (rex) == 1);
assert (streq (zrex_hit (rex, 0), "123-456-789"));
assert (zrex_hit (rex, 1) == NULL);
zrex_destroy (&rex);

//  Here we pick out hits using capture groups
rex = zrex_new ("(\\d+)-(\\d+)-(\\d+)");
assert (rex);
assert (zrex_valid (rex));
matches = zrex_matches (rex, "123-456-ABC");
assert (!matches);
matches = zrex_matches (rex, "123-456-789");
assert (matches);
assert (zrex_hits (rex) == 4);
assert (streq (zrex_hit (rex, 0), "123-456-789"));
assert (streq (zrex_hit (rex, 1), "123"));
assert (streq (zrex_hit (rex, 2), "456"));
assert (streq (zrex_hit (rex, 3), "789"));
zrex_destroy (&rex);

//  This shows the pattern of matching one line against many
//  patterns and then handling the case when it hits
rex = zrex_new (NULL);      //  No initial pattern
assert (rex);
char *input = "Mechanism: CURVE";
matches = zrex_eq (rex, input, "Version: (.+)");
assert (!matches);
assert (zrex_hits (rex) == 0);
matches = zrex_eq (rex, input, "Mechanism: (.+)");
assert (matches);
assert (zrex_hits (rex) == 2);
const char *mechanism;
zrex_fetch (rex, &mechanism, NULL);
assert (streq (zrex_hit (rex, 1), "CURVE"));
assert (streq (mechanism, "CURVE"));
zrex_destroy (&rex);

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