PHP Learning Regular Expressions Courseware Page 1/2_PHP Tutorial

Regular expressions

There are two sets of regular expression function libraries in PHP. The functions of the two are similar, but their execution efficiency is slightly different:
One set is provided by the PCRE (Perl Compatible Regular Expression) library . Functions named with the prefix "preg_";
A set provided by POSIX (Portable Operating System Interface of Unix) extensions (PHP default). Use functions named with the prefix "ereg_";
In PHP, regular expressions have three functions:
Matching is also often used to extract information from strings.
Replace the matched text with new text.
Split a string into a set of smaller chunks of information.

A regular expression contains at least one atom.
Atoms (ordinary characters, such as English characters)
Metacharacters (characters with special functions)
Pattern modification characters (modifications to regular expression semantics)


Atoms ( Atom)
Single characters, numbers, such as a~z, A~Z, 0~9.
Pattern units such as (ABC) can be understood as large atoms composed of multiple atoms.
Atomic table, such as [ABC].
Reused pattern units, such as: \1
Common escape characters, such as: d, D, w
Escape metacharacters, such as: *,.

POSIX regular expression The full name of POSIX regular expression is Portable Operating System Interface of Unix, which means UNIX portable operating system implementation interface.

Constructing POSIX regular expressions is the same as creating mathematical expressions, that is, using a variety of metacharacters and operators to combine small expressions to create larger expressions.


Meta-characters
Meta-characters are characters with special meanings used to construct regular expressions.If you want to include the metacharacter itself in the regular expression, you must escape it with "" in front of it.
Metacharacter Description
* Matches the preceding atom
+ 0 times, 1 time or multiple times Matches the preceding atom
1 or more times? Matches the preceding atom
0 or 1 times | Matches two or more choices such as [1-9]|[a-b]|[A-Z] Matches any atom that matches true
^ Matches the atom at the beginning of the string For example, abscd===^afdgfgf Matches
$ Matches the atom at the end of the string For example, dasdsv===v$
[] Matches Any atom in square brackets For example s===[dsadas]
[^] Matches any character except the atoms in square brackets For example aaaaa===[dddd]
{m} Represents its previous atom Appearing exactly m times
{m,n} means that the previous atom appears at least m times, and at least n times (n>m)
{m,} means that the previous atom appears no less than m times
() The whole represents an atom
. Matches any character except newline

^ $ These two original characters together are called delimited
abd===^abc$ Only like this Only match

Pattern matching order
order Metacharacter Description
1 () Pattern unit
2 ? * +{} Repeat match
3 ^$ Boundary restriction
4 | Pattern selection

POSIX regular expression functions
ereg() and eregi()
ereg_replace() and eregi_replace ()
split() and spliti()

ereg() and eregi() ereg() string matching functions, eregi() is the size-ignoring version of the ereg() function
syntax Format: if (!ereg('^[^./][^/]*$', $userfile))//Does not match the format output die
{
die('This is an illegal file name ! ');
}

ereg_replace() and eregi_replace (ignoring case) replace
string eregi_replace ("regular expression", "target replacement character", "replacement target")
Grammar format: $string = "This is a test";
echo str_replace(" is", "was", $string);
echo ereg_replace("( )is", "\1was", $ string);\1 Inherit the first whole
echo ereg_replace("(( )is)", "\2was", $string);\2 Inherit the second whole

split() Use regular expressions to split strings into arrays with spliti (ignoring case)
list: assign some variables to the values ​​in the array
Syntax format: $date = "04/30/1973";
list($month, $day, $year) = split ('[/.-]', $date);//List the corresponding formats of the three variables//In what form to split and who to split
echo "Month: $month; Day: $day; Year: $year
n";
Output result Month: 04; Day: 30; Year: 1973

http://www.bkjia.com/PHPjc/319085.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/319085.htmlTechArticleRegular expressions There are two sets of regular expression function libraries in PHP. The functions of the two are similar, but the execution efficiency is slightly There are differences: One set is provided by the PCRE (PerlCompatibleRegularExpression) library. ...