Regular Expression Any Character PHP Learning Regular Expression Courseware Page 1/2

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, and are often used to extract information from strings.
Replace matching 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 correction characters (modifications to the semantics of regular expressions)
   Atom (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 expressions
POSIX regular expressions are called Portable Operating System Interface of Unix 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-character
Meta-characters are characters with special meanings used to construct regular expressions.If you want to include the Yuan character itself in the regular expression, you must add "" to the "" to the righteousness. The atom before it
? Matches the atom before it 0 or 1 times
| Matches two or more selections such as [1-9]|[a-b]|[A-Z] Matches any of them as true
^ Matching characters The atom at the beginning of the string, for example, abscd===^afdgfgf, matches the atom at the end of the string, for example, dasdsv===v$,
[], ​​matches any atom in the square brackets, for example, s===[dsadas]
[^] Matches any characters except atoms in square brackets. For example, aaaaa===[dddd]
{m} means that the preceding atom appears exactly m times.
{m,n} means that the preceding atom appears at least m times, at least Appearing n times (n>m)
{m,} means that the preceding atom appears no less than m times
() The whole represents an atom
. Matches any character except line breaks
^ $ These two original characters are in Together they are called delimited
abd===^abc$ Only in this way can we match
Order of pattern matching
Order Metacharacter Description
1 () Pattern unit
2 ? * +{} Repeat matching
3 ^$ Boundary restrictions 4 place()
split() and spliti()
ereg( ) and eregi()ereg() string matching function, eregi() is the size-ignoring version of the ereg() function
Syntax format: if (!ereg('^[^./][^/]*$', $userfile))//Mismatching format output die
{
die('This is an illegal file name!');
}
ereg_replace() and eregi_replace (ignore 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 inherits the first whole
echo ereg_replace("(( )is)", "\2was", $string);\2 inherits the second whole
split () and spliti (ignoring case) use regular expressions to split the string into an array
list: assign some variables to the values ​​in the array
Grammar 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 results Month: 04; Day: 30; Year: 1973

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