regular expressions in php

1. Strings
TYBSc. Comp. Sci.
Chapter 2- Functions & Strings
monica deshmane(H.V.Desai college) 1

2. Points to learn
String
• Regular expressions
• POSIX
• Perl Compatible
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1. Matching
$b = ereg(pattern, string [,captured]);
Depending on match it returns count for number of
matches and also populates the array.
echo "<br>".ereg('c(.*)e$','Welcome', $arr);
echo "<br>";
print_r($arr);
Output:
4
Array ( [0] => come [1] => om )
0th element is set to the entire string being matched and 1st element is substring that matched.
Regular Expression
1.POSIX
Uses of POSIX Functions

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$email_id = "admin@tutorialspoint.com";
$retval =preg_match("/.com$/", $email_id);
if( $retval == true )
{
echo "Found a .com<br>";
} else {
echo "Could not found a .com<br>";
}
Try this-

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<?php
$email = "abc123@sdsd.com";
$regex = '/^([a-z0-9])+@([a-z0-9])+.([a-z]{2,3})$/';
if (preg_match($regex, $email)) {
echo $email . " is a valid email. We can accept it.";
} else {
echo $email . " is an invalid email. Please try again.";
}
?>
Email validation

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2.Replacing
$str = ereg_replace(pattern, replacement, string)
The ereg_replace() function searches for string
specified by pattern and replaces pattern with
replacement if found.
Like ereg(), ereg_replace() is case sensitive.
eregi_replace is case insesnsitive.
It returns the modified string, but if no matches are
found, the string will remain unchanged.
e.g.
$copy_date = “june1999";
$copy_date1 = ereg_replace("([0-9]+)", "2000", $copy_date);
print $copy_date1;
Output: june2000
Regular Expression
1.POSIX
Uses of POSIX Functions

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<?php
$s="hi , php, 2";
$arr=preg_split("/,/",$s);
print_r($arr);
?>
3. splitting

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Similarly ,
Try for
1) Extract information-
matching- Preg_match()
2) Substitution-
replacing- Preg_replace()
3) Splitting- Preg_split()

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1. Searching pattern at the start of string(^)
$b = ereg('^We', 'Welcome to PHP Program');
echo $b;
2. Searching pattern at the end of string($)
$b = ereg('We$', 'Welcome to PHP Program');
echo $b;
3. Dot (.)/period operator Used to match single character
echo "<br>".ereg('n.t', 'This is not a word'); //1
echo "<br>".ereg('n.t', 'nut is not here'); //1
echo "<br>".ereg('n.t', 'Take this bat'); //0
echo "<br>".ereg('n.t', 'n t'); //1
echo "<br>".ereg('n.t', 'nt'); //0
Regular Expression
1.POSIX Basics of Regular Expression

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3. Splitting
$arr = ereg_split(pattern, string[, limit])
The split() function will divide a string into various elements,
the boundaries of each element based on the occurrence of pattern in string.
The optional parameter limit is used to show the number of elements
into which the string should be divided,
starting from the left end of the string and working rightward.
In cases where the pattern is an alphabetical character, split() is case sensitive.
It returns an array of strings after splitting up a string.
Regular Expression
1.POSIX
Uses of POSIX Functions

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4. Matching special character /meta character use backslash or escape.
echo ereg(‘$50.00', 'Bill amount is $50.00'); //1
echo ereg(‘$50.00', 'Bill amount is $50.00'); //0
RE are case sensitive by default.
To perform case insensitive use eregi() used.
Abstract patterns-
1)Character class
2)Alternatives
3)Repeating sequences
Regular Expression
1.POSIX Basics of Regular Expression

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Character class is used to specify set of acceptable
characters in pattern.
defined by enclosing the acceptable characters in square bracket.
• Acceptable characters are-alphabets,numeric,punctuation marks.
• alphabets
echo "<br>".ereg('ch[aeiou]t', 'This is online chat'); //1
echo "<br>".ereg('ch[aeiou]t', 'See the chit'); //1
echo "<br>".ereg('ch[aeiou]t', ‘charitable'); //0
Regular Expression
Abstract patterns 1) Character classes

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•negate/except
Specify the ^ sign at the start of character class, this will negate/except the condition.
echo "<br>".ereg('ch[^aeiou]t', 'This is online chat'); //0
echo "<br>".ereg('ch[^aeiou]t', 'See the chit'); //0
echo "<br>".ereg('ch[^aeiou]t', 'chrt'); //1
• Use hypen(-) to specify the range of characters.
echo "<br>".ereg('[0-9]th', ‘This number is 10th'); //1
echo "<br>".ereg('[0123456789]th', This number is 7th'); //1
echo "<br>".ereg('[a-z]e', 'Welcome to internet Programming'); //1
echo "<br>".ereg('[a-z][A-Z]e', 'Welcome to internet Programming '); //1
Regular Expression
Abstract patterns
1) Character classes

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Character classes
[:alnum:] Alphanumeric characters [0-9a-zA-Z]
[:alpha:] Alphabetic characters [a-zA-Z]
[:blank:] space and tab [ t]
[:digit:] Digits [0-9]
[:lower:] Lower case letters [a-z]
[:upper:] Uppercase letters [A-Z]
[:xdigit:] Hexadecimal digit [0-9a-fA-F]
range of characters ex. [‘aeiou’]
Range ex. [2,6]
for special character Ex . [‘$’]
echo ereg('[[:digit:]]','23432434'); //1
echo ereg(‘[0-9]','23432434'); //1
Regular Expression
Abstract patterns 1) Character classes

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Vertical Pipe(|) symbol is used to specify alternatives.
echo "<br>".ereg('Hi|Hello', 'Welcome, Hello guys'); //1
echo "<br>".ereg('Hi|Hello', 'Welcome, Hi ameya'); //1
echo "<br>".ereg('Hi|Hello', 'Welcome, how are u?'); //0
String start with Hi or ends with Hello
echo "<br>".ereg('^Hi|Hello$', 'Hi, are u there?'); //1
echo "<br>".ereg('^Hi|Hello$', 'Hello, are u fine?'); //0
echo "<br>".ereg('^Hi|Hello$', 'how do u do?, Hello');//1
Regular Expression
Abstract patterns 2) Alternatives

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? 0 or 1
* 0 or more
+ 1 or more
{n} Exactly n times
{n,m} Atleast n, no more than m times
{n,} Atleast n times
echo "<br>".ereg('Hel+o', 'Hellllo'); //1
echo "<br>".ereg('Hel+o', 'Helo'); //0
echo "<br>".ereg('Hel?o', 'Helo'); //1
echo "<br>".ereg('Hel*o', 'Hellllo'); //1
echo "<br>".ereg('[0-9]{3}-[0-9]{3}-[0-9]{4}', '243-543-3567‘); //1
Regular Expression
Abstract patterns
3) Repeating Sequences

17. Subpatterns
echo "<br>".ereg('a (very )+good', 'Its a very very
good idea'); //1
Parentheses is used to group bits of regular
expression.
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18. preg_grep
preg_grep ( string $pattern , array $input [, int $flags = 0 ] ) :
Return array entries that match the pattern
Returns an array indexed using the keys from the input array.
$input = [ "Redish", "Pinkish", "Greenish","Purple"];
$result = preg_grep("/^p/i", $input);
print_r($result);
?>
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19. perl compatible RE-
1.preg_match()-matches 1st match to pattern.
2.preg_match_all()-all matches.
3.preg_replace()
4. preg_split()
5.Preg_grep()
6.preg_quote()
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Uses

20. End of Presentation
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