preg_grep()

(PHP 4, PHP 5, PHP 7)

返回匹配模式的数组条目

说明

preg_grep(string $pattern,array $input[,int $flags= 0]): array

返回给定数组$input中与模式$pattern匹配的元素组成的数组.

参数

$pattern: 要搜索的模式,字符串形式.
$input: 输入数组.
$flags: 如果设置为PREG_GREP_INVERT,这个函数返回输入数组中与给定模式$pattern不匹配的元素组成的数组.

返回值

返回使用$input中key做索引的数组.

范例

preg_grep()示例

<?php
// 返回所有包含浮点数的元素
$fl_array = preg_grep("/^(\d+)?\.\d+$/", $array);
?>

参见

PCRE 模式
preg_quote()转义正则表达式字符
preg_match_all()执行一个全局正则表达式匹配
preg_filter()执行一个正则表达式搜索和替换
preg_last_error()返回最后一个PCRE正则执行产生的错误代码

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)));
}
?>

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;
}
?>

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

An even shorter way to run a match on the array's keys rather than the values:
<?php
function preg_grep_keys($pattern, $input, $flags = 0) {
  return array_flip( preg_grep($pattern, array_flip($input), $flags ) );
}
?>