regexp.html

unix 下的C开发手册,还用详细的例程。

(Concatenation.)

<dt><i>r</i>\{<i>m</i>,<i>n</i>\}<dd>Any number of
<i>m</i>
through
<i>n</i>
successive occurrences of the regular expression
<i>r</i>.
The regular expression
<i>r</i>\{<i>m</i>\}
matches exactly
<i>m</i>
occurrences,
<i>r</i>\{<i>m</i>,\}
matches at least
<i>m</i>
occurrences.  The maximum number of occurrences is matched.

<dt>\(<i>r</i>\)<dd>The regular expression
<i>r</i>.
The
<i>\(</i>
and
<i>\)</i>
sequences are ignored.

<dt>\<i>n</i><dd>When
<i>\n</i>
(where
<i>n</i>
is a number in the range 1 to 9) appears in a concatenated
regular expression, it stands for the regular expression
<i>x</i>,
where
<i>x</i>
is the
<i>n</i>th
regular expression enclosed in \( and \)
sequences that appeared
earlier in the concatenated regular expression.
For example, in the pattern
<i>\(r\)x\(y</i>
the
<i>\2</i>
matches the regular expression
<i>y</i>,
giving
<i>rxyzy</i>.

</dl>
<p>
Characters that have special meaning except where they appear within
square brackets, [] , or are preceded by "\" are:
<pre>
<code>
</code>
</pre>
Other special characters, such as $ have special meaning in more
restricted contexts.
<p>
The character "^"
at the beginning of an expression permits a successful
match only immediately after a newline or at the beginning of
each of the strings to which the match is applied, and the character
"$" at the end of an expression requires a trailing newline.
<p>
Two characters have special meaning only when used within square
brackets.
The character "-" denotes a range, [<i>c</i> - <i>c</i> ],
unless it is just after the left square bracket or before the
right square bracket, [-<i>c</i> ]
or [<i>c</i> -],
in which case it has no special meaning.
The character "^" has the meaning
<i>complement of</i>
if it immediately follows the left square bracket, [^<i>c</i> ].
Elsewhere between brackets, [
<i>c</i>^],
it stands for the ordinary character "^".
The right square bracket (]) loses its special meaning and
represents itself in a bracket expression if it occurs first in
the list after any initial circumflex (^) character.
<p>
The special meaning of the "\" operator can be escaped
<i>only</i>
by preceding it with another "\"; that is, "\\".
<br>
<h5><a name = "tag_000_008_059_003">&nbsp;</a>SRE Operator Precedence</h5>
The precedence of the operators is as shown below:
<dl compact>

<dt>[...]<dd>High precedence.

<dt>*<dd>
<dt>concatenation<dd>Low precedence.

</dl>
<h5><a name = "tag_000_008_059_004">&nbsp;</a>Internationalised SREs</h5>
Character expressions within square brackets are constructed as
follows:
<dl compact>

<dt><b>Expression</b><dd><b>Meaning</b>

<dt><i>c</i><dd>The single character
<i>c</i>
where
<i>c</i>
is not a special character.


<dt>[[:<i>class</i>:]]<dd>A character class expression.  Any character of type
<i>class</i>,
as defined by category LC_CTYPE
in the program's locale (see the <b>XBD</b> specification, <a href="../xbd/locale.html"><b>Locale</b>&nbsp;</a>).
For
<i>class</i>,
one of the following should be substituted:
<dl compact>

<dt>alpha<dd>A letter.

<dt>upper<dd>An upper-case letter.

<dt>lower<dd>A lower-case letter.

<dt>digit<dd>A decimal digit.

<dt>xdigit<dd>A hexadecimal digit.

<dt>alnum<dd>An alphanumeric (letter or digit).

<dt>space<dd>A character producing white space in displayed text.

<dt>punct<dd>A punctuation character.

<dt>print<dd>A printing character.

<dt>graph<dd>A character with a visible representation.

<dt>cntrl<dd>A control character.

</dl>
<p>
<dt>[[<i>=c=</i>]]<dd>An equivalence class.  Any collation element defined as having the same
relative order in the current collation sequence as
<i>c</i>.
As an example, if
<b>A</b>
and
<b>a</b>
belong to the same equivalence class, then both [[<i>=A=</i>]<i>b</i>]
and [[
<i>=a=</i>]<i>b</i>]
are equivalent to [
<i>Aab</i>].
<br>
<p>
<dt>[[<i>.cc.</i>]]<dd>A collating symbol.  Multi-character collating elements must be
represented as collating symbols to distinguish them from
single-character collating elements.  As an example, if the string
<i>ch</i>
is a valid collating element, then [[
<i>.ch.</i>]]
will be treated as an element matching the same string
of characters, while
<i>ch</i>
will be treated as a simple list of
<i>c</i>
and
<i>h</i>.
If the string is not a valid collating element in the current
collating sequence definition, the symbol will be treated as an
invalid expression.
<p>
<dt>[<i>c-c</i>]<dd>Any collation element in the character expression range
<i>c-c</i>,
where
<i>c</i>
can identify a collating symbol or an equivalence class.
If the character "-" appears immediately after an opening
square bracket (for example, [-<i>c</i>]) or immediately prior to
a closing square bracket (for example, [<i>c</i>-]), it has no
special meaning.
<p>
<dt>^<dd>Immediately following an opening square
bracket, means the complement of, for example, [^<i>c</i>].
Otherwise, it has no special meaning.
<p>
</dl>
<p>
Within square brackets, a "." that is not part of a [[
<i>.cc.</i>]]
sequence, or a ":" that is not part of a [[:<i>class</i>:]]
sequence, or an "=" that is not part of a [[<i>=c=</i>]]
sequence, matches itself.
<br>
<h5><a name = "tag_000_008_059_005">&nbsp;</a>SRE Examples</h5>
Below are examples of regular expressions:
<p><table  bordercolor=#000000 border=1 align=center><tr valign=top><th align=center><b>Pattern</b>
<th align=center><b>Meaning</b>
<tr valign=top><td align=left>ab.d
<td align=left>ab <i>any character</i> d
<tr valign=top><td align=left>ab.*d
<td align=left>ab <i>any sequence of characters (including none)</i> d
<tr valign=top><td align=left>ab[xyz]d
<td align=left>ab <i>one of </i>x y <i>or</i> z d
<tr valign=top><td align=left>ab[c]d
<td align=left>ab <i>anything except </i>c d
<tr valign=top><td align=left>abcd$
<td align=left><i>a line containing only</i> abcd
<tr valign=top><td align=left>[a-d]
<td align=left><i>any one of</i> a b c <i>or</i> d
</table>
<p>
These interfaces need not be reentrant.
</blockquote><h4><a name = "tag_000_008_060">&nbsp;</a>RETURN VALUE</h4><blockquote>
The
<i><a href="compile.html">compile()</a></i>
function uses the macro RETURN() on success and the macro ERROR()
on failure, see above.
The
<i><a href="step.html">step()</a></i>
and
<i><a href="advance.html">advance()</a></i>
functions return non-zero on a successful match and 0 if there is no match.
</blockquote><h4><a name = "tag_000_008_061">&nbsp;</a>ERRORS</h4><blockquote>
<dl compact>

<dt>11<dd>Range endpoint too large.

<dt>16<dd>Bad number.

<dt>25<dd>\digit out of range.

<dt>36<dd>Illegal or missing delimiter.

<dt>41<dd>No remembered search string.

<dt>42<dd>\( \) imbalance.

<dt>43<dd>Too many \( .

<dt>44<dd>More than two numbers given in \{ \} .

<dt>45<dd>} expected after \ .

<dt>46<dd>First number exceeds second in \{ \} .

<dt>49<dd>[  ] imbalance.

<dt>50<dd>Regular expression overflow.

</dl>
</blockquote><h4><a name = "tag_000_008_062">&nbsp;</a>EXAMPLES</h4><blockquote>
The following is an example of how the regular expression macros and
calls might be defined by an application program:
<pre>
<code>
#define INIT         char *sp = instring;
#define GETC()     (*sp++)
#define PEEKC()    (*sp)
#define UNGETC(c)    (--sp)
#define RETURN(c)    return;
#define ERROR(c)     regerr()

#include &lt;regexp.h&gt;
    (void) compile(*argv, expbuf, &amp;expbuf[ESIZE], \0);
    if (step(linebuf, expbuf) )
        succeed();
</code>
</pre>
</blockquote><h4><a name = "tag_000_008_063">&nbsp;</a>APPLICATION USAGE</h4><blockquote>
Applications should migrate to the
<i><a href="fnmatch.html">fnmatch()</a></i>,
<i><a href="glob.html">glob()</a></i>,
<i><a href="regcomp.html">regcomp()</a></i>
and
<i><a href="regexec.html">regexec()</a></i>
functions which provide full internationalised regular expression
functionality compatible with the ISO POSIX-2 standard, as described in the <b>XBD</b> specification, <a href="../xbd/re.html"><b>Regular Expressions</b>&nbsp;</a>.
</blockquote><h4><a name = "tag_000_008_064">&nbsp;</a>FUTURE DIRECTIONS</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_008_065">&nbsp;</a>SEE ALSO</h4><blockquote>
<i><a href="fnmatch.html">fnmatch()</a></i>,
<i><a href="glob.html">glob()</a></i>,
<i><a href="regcomp.html">regcomp()</a></i>,
<i><a href="regexec.html">regexec()</a></i>,
<i><a href="setlocale.html">setlocale()</a></i>,
<i><a href="regex.h.html">&lt;regex.h&gt;</a></i>,
<i><a href="regexp.h.html">&lt;regexp.h&gt;</a></i>,
the <b>XBD</b> specification, <a href="../xbd/re.html"><b>Regular Expressions</b>&nbsp;</a>.
</blockquote><h4>DERIVATION</h4><blockquote>
Derived from Issue 2 of the SVID.
</blockquote><hr size=2 noshade>
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Copyright &copy; 1997 The Open Group
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