preg_grep
(PHP 4, PHP 5)
preg_grep — Return array entries that match the pattern
Description
$pattern
, array $input
[, int $flags = 0
] )
Returns the array consisting of the elements of the
input array that match the given
pattern.
Parameters
-
pattern -
The pattern to search for, as a string.
-
input -
The input array.
-
flags -
If set to
PREG_GREP_INVERT, this function returns the elements of the input array that do not match the givenpattern.
Return Values
Returns an array indexed using the keys from the
input array.
Changelog
| Version | Description |
|---|---|
| 4.2.0 |
The flags parameter was added.
|
| 4.0.4 |
Prior to this version, the returned array was indexed regardless of
the keys of the If you want to reproduce this old behavior, use array_values() on the returned array to reindex the values. |
Examples
Example #1 preg_grep() example
<?php
// return all array elements
// containing floating point numbers
$fl_array = preg_grep("/^(\d+)?\.\d+$/", $array);
?>
See Also
- PCRE Patterns
- preg_match_all() - Perform a global regular expression match
- preg_filter() - Perform a regular expression search and replace
- preg_last_error() - Returns the error code of the last PCRE regex execution
Коментарии
Run a match on the array's keys rather than the values:
<?php
function preg_grep_keys( $pattern, $input, $flags = 0 )
{
$keys = preg_grep( $pattern, array_keys( $input ), $flags );
$vals = array();
foreach ( $keys as $key )
{
$vals[$key] = $input[$key];
}
return $vals;
}
?>
A shorter way to run a match on the array's keys rather than the values:
<?php
function preg_grep_keys($pattern, $input, $flags = 0) {
return array_intersect_key($input, array_flip(preg_grep($pattern, array_keys($input), $flags)));
}
?>
This may be obvious to most experienced developers,but just in case its not,when using preg_grep to check for whitelisted items ,one must be very careful to explicitly define the regex boundaries or it will fail
<?php
$whitelist = ["home","dashboard","profile","group"];
$possibleUserInputs = ["homd","hom","ashboard","settings","group"];
foreach($possibleUserInputs as $input)
{
if(preg_grep("/$input/i",$whitelist)
{
echo $input." whitelisted";
}else{
echo $input." flawed";
}
}
?>
This results in:
homd flawed
hom whitelisted
ashboard whitelisted
settings flawed
group whitelisted
I think this is because if boundaries are not explicitly defined,preg_grep looks for any instance of the substring in the whole array and returns true if found.This is not what we want,so boundaries must be defined.
<?php
foreach($possibleUserInputs as $input)
{
if(preg_grep("/^$input$/i",$whitelist)
{
echo $input." whitelisted";
}else{
echo $input." flawed";
}
}
?>
this results in:
homd flawed
hom flawed
ashboard flawed
settings flawed
group whitelisted
in_array() will also give the latter results but will require few tweaks if say,the search is to be case insensitive,which is always the case 70% of the time