International PHP Conference 2019 - Spring Edition

メタ文字

正規表現の強力さは、パターン中に選択肢や繰り返しを記述できることに あります。選択肢や繰り返しは、メタ文字 (meta-character) を使ってパターン中に記述します。メタ文字は、 その文字自体を表わさず、代わって特別な解釈が行われます。

メタ文字には、2 種類あります。ひとつは、角カッコ内を除き、 パターン中のどこででも使用できる文字です。もうひとつは、 角カッコで括られた中でだけ使用できる文字です。

前者の角カッコ外で使用できるメタ文字には、次のものがあります。

角カッコ外で使用できるメタ文字
メタ文字説明
\多目的に使う一般的なエスケープ文字
^検索対象(複数行モードでは行)の始まりを言明
$検索対象の終わりあるいは終端の改行文字の前(複数行モードでは行の終わり)を言明
.改行を除くすべての文字にマッチ(デフォルト時)
[文字クラス定義の開始
]文字クラス定義の終了
|選択枝の開始
(サブパターンの開始
)サブパターンの終了
?( の意味を拡張/0 または 1 回マッチ/なるべく少ない回数だけマッチ (繰り返し を参照)
*0 回以上の繰り返し
+1 回以上の繰り返し
{最小/最大を指定する量指定子の開始
}最小/最大を指定する量指定子の終了
パターン中の角カッコで括まれた部分を「文字クラス」と言います。 文字クラスで使えるメタ文字は、次のものだけです。
角カッコ内のメタ文字 (文字クラス)
Meta-characterDescription
\一般的なエスケープ文字
^クラスの否定。ただし、文字クラスの最初の文字に用いた場合のみ
-文字の範囲の指定
以降のセクションで、各メタ文字の使用法の説明を行います。

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User Contributed Notes 5 notes

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0
Wirek
7 months ago
An important addendum (with new $pat3_2 utilising \R properly, its results and comments):
Note that there are (sometimes difficult to grasp at first glance) nuances of meaning and application of escape sequences like \r, \R and \v - none of them is perfect in all situations, but they are quite useful nevertheless. Some official PCRE control options and their changes come in handy too - unfortunately neither (*ANYCRLF), (*ANY) nor (*CRLF) is documented here on php.net at the moment (although they seem to be available for over 10 years and 5 months now), but they are described on Wikipedia ("Newline/linebreak options" at https://en.wikipedia.org/wiki/Perl_Compatible_Regular_Expressions) and official PCRE library site ("Newline convention" at http://www.pcre.org/original/doc/html/pcresyntax.html#SEC17) pretty well. The functionality of \R appears somehow disappointing (with default configuration of compile time option) according to php.net as well as official description ("Newline sequences" at https://www.pcre.org/original/doc/html/pcrepattern.html#newlineseq) when used improperly.

A hint for those of you who are trying to fight off (or work around at least) the problem of matching a pattern correctly at the end (or at the beginning) of any line even without the multiple lines mode (/m) or meta-character assertions ($ or ^).
<?php
// Various OS-es have various end line (a.k.a line break) chars:
// - Windows uses CR+LF (\r\n);
// - Linux LF (\n);
// - OSX CR (\r).
// And that's why single dollar meta assertion ($) sometimes fails with multiline modifier (/m) mode - possible bug in PHP 5.3.8 or just a "feature"(?) of default configuration option for meta-character assertions (^ and $) at compile time of PCRE.
$str="ABC ABC\n\n123 123\r\ndef def\rnop nop\r\n890 890\nQRS QRS\r\r~-_ ~-_";
//          C          3                   p          0                   _
$pat3='/\w\R?$/mi';    // Somehow disappointing according to php.net and pcre.org when used improperly
$pat3_2='/\w(?=\R)/i';    // Much better with allowed lookahead assertion (just to detect without capture) without multiline (/m) mode; note that with alternative for end of string ((?=\R|$)) it would grab all 7 elements as expected, but '/(*ANYCRLF)\w$/mi' is more straightforward in use anyway
$p=preg_match_all($pat3, $str, $m3);
$r=preg_match_all($pat3_2, $str, $m4);
echo
$str."\n3 !!! $pat3 ($p): ".print_r($m3[0], true)
    .
"\n3_2 !!! $pat3_2 ($r): ".print_r($m4[0], true);
// Note the difference between the two very helpful escape sequences in $pat3 and $pat3_2 (\R) - for some applications at least.

/* The code above results in the following output:
ABC ABC

123 123
def def
nop nop
890 890
QRS QRS

~-_ ~-_
3 !!! /\w\R?$/mi (5): Array
(
    [0] => C

    [1] => 3
    [2] => p
    [3] => 0
    [4] => _
)

3_2 !!! /\w(?=\R)/i (6): Array
(
    [0] => C
    [1] => 3
    [2] => f
    [3] => p
    [4] => 0
    [5] => S
)
*/
?>
Unfortunately, I haven't got any access to a server with the latest PHP version - my local PHP is 5.3.8 and my public host's PHP is version 5.2.17.
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0
Wirek
7 months ago
Significantly updated version (with $pat4 and the best $pat5!):
A hint for those of you who are trying to fight off (or work around at least) the problem of matching a pattern correctly at the end ($) of any line in multiple lines mode (/m).
<?php
// Various OS-es have various end line (a.k.a line break) chars:
// - Windows uses CR+LF (\r\n);
// - Linux LF (\n);
// - OSX CR (\r).
// And that's why single dollar meta assertion ($) sometimes fails with multiline modifier (/m) mode - possible bug in PHP 5.3.8 or just a "feature"(?).
$str="ABC ABC\n\n123 123\r\ndef def\rnop nop\r\n890 890\nQRS QRS\r\r~-_ ~-_";
//          C          3                   p          0                   _
$pat1='/\w$/mi';
$pat2='/\w\r?$/mi';
$pat3='/\w\R?$/mi';
$pat4='/\w\v?$/mi';
$pat5='/(*ANYCRLF)\w$/mi';
$n=preg_match_all($pat1, $str, $m1);
$o=preg_match_all($pat2, $str, $m2);
$p=preg_match_all($pat3, $str, $m3);
$r=preg_match_all($pat4, $str, $m4);
$s=preg_match_all($pat5, $str, $m5);
echo
$str."\n1 !!! $pat1 ($n): ".print_r($m1[0], true)
    .
"\n2 !!! $pat2 ($o): ".print_r($m2[0], true)
    .
"\n3 !!! $pat3 ($p): ".print_r($m3[0], true)
    .
"\n4 !!! $pat4 ($r): ".print_r($m4[0], true)
    .
"\n5 !!! $pat5 ($s): ".print_r($m5[0], true);
// Note the difference between the three very helpful escape sequences in $pat2 (\r), $pat3 (\R), $pat4 (\v) and altered newline option in $pat5 ((*ANYCRLF)) - for some applications at least.

/* The code above results in the following output:
ABC ABC

123 123
def def
nop nop
890 890
QRS QRS

~-_ ~-_
1 !!! /\w$/mi (3): Array
(
    [0] => C
    [1] => 0
    [2] => _
)

2 !!! /\w\r?$/mi (5): Array
(
    [0] => C
    [1] => 3
    [2] => p
    [3] => 0
    [4] => _
)

3 !!! /\w\R?$/mi (5): Array
(
    [0] => C

    [1] => 3
    [2] => p
    [3] => 0
    [4] => _
)

4 !!! /\w\v?$/mi (5): Array
(
    [0] => C

    [1] => 3
    [2] => p
    [3] => 0
    [4] => _
)

5 !!! /(*ANYCRLF)\w$/mi (7): Array
(
    [0] => C
    [1] => 3
    [2] => f
    [3] => p
    [4] => 0
    [5] => S
    [6] => _
)
*/
?>
Unfortunately, I haven't got any access to a server with the latest PHP version - my local PHP is 5.3.8 and my public host's PHP is version 5.2.17.
up
-1
Wirek
7 months ago
A hint for those of you who are trying to fight off (or work around at least) the problem of matching a pattern correctly at the end ($) of any line in multiple lines mode (/m).
<?php
// Various OS-es have various end line (a.k.a line break) chars:
// - Windows uses CR+LF (\r\n);
// - Linux LF (\n);
// - OSX CR (\r).
// And that's why single dollar meta assertion ($) sometimes fails with multiline modifier (/m) mode - possible bug in PHP 5.3.8(?).
$str="ABC ABC\n\n123 123\r\ndef def\rnop nop\r\n890 890\nQRS QRS\r\r~-_ ~-_";
//          C          3                   p          0                   _
$pat1='/\w$/mi';
$pat2='/\w\r?$/mi';
$pat3='/\w\R?$/mi';
$n=preg_match_all($pat1, $str, $m1);
$o=preg_match_all($pat2, $str, $m2);
$p=preg_match_all($pat3, $str, $m3);
echo
$str."\n1 !!! $pat1 ($n): ".print_r($m1[0], true)
    .
"\n2 !!! $pat2 ($o): ".print_r($m2[0], true)
    .
"\n3 !!! $pat3 ($p): ".print_r($m3[0], true);
// Note the difference between the two very helpful escape sequences in $pat2 (\r) and in $pat3 (\R) - for some applications at least.

/* The code above results in the following output:
ABC ABC

123 123
def def
nop nop
890 890
QRS QRS

~-_ ~-_
1 !!! /\w$/mi (3): Array
(
    [0] => C
    [1] => 0
    [2] => _
)

2 !!! /\w\r?$/mi (5): Array
(
    [0] => C
    [1] => 3
    [2] => p
    [3] => 0
    [4] => _
)

3 !!! /\w\R?$/mi (5): Array
(
    [0] => C

    [1] => 3
    [2] => p
    [3] => 0
    [4] => _
)
*/
?>
Unfortunately, I haven't got any access to a server with the latest PHP version - my local PHP is 5.3.8 and my public host's PHP is version 5.2.17.
up
-2
Kurt Wei
2 years ago
disturbing usage of "any character" for multi-lines...

remark:
'.' (all characters) just does NOT include on single character the newline (\n) by default,
while \n is included in all other matching searches (e.g. \s).
Funny enough, the "carriage return" (\r) is included, when using '.'

You have to write "(.|\\n)" instead of a single dot, with disadvantages in using complex matching-results,

or simple use the "s" modificator to bring dot to accept the newline.

$subject="<tag>Hello\nWorld</tag>";

preg_match( '/<tag>[A-Za-z\\s]*<\\/tag>/' , $subject ); //true
preg_match( '/<tag>[^<]*<\\/tag>/' , $subject ); //true
preg_match( '/<tag>(.|\\n)*<\\/tag>/' , $subject ); //true
preg_match( '/<tag>.*<\\/tag>/s' , $subject ); //true
preg_match( '/<tag>.*<\\/tag>/' , $subject ); //ATTENTION! *false*
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-33
Thomas
3 years ago
The meta character $ accepts a (one) newline character (\n).

(Take a moment to let this information sink in)

You might want to (r)trim() your input afterwards if you have a match because otherwise it (still) might not meet a length requirement or other strange stuff might happen when you store the input as-is.
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