a drop-in replacement for ereg* functions in PHP

ere2pcre.php

<?php
// ere2pcre -- a drop-in replacement for ereg* functions
// written by Kang Seonghoon <public+ere2pcre@mearie.org>.
//
// this library is dedicated to the public domain. for the jurisdictions that
// does not recognize the public domain, CC0 1.0 Universal Public Domain
// Dedication applies.

function _ere2pcre_escape($c) {
    if ($c == "\0") {
        trigger_error('ere2pcre: a literal null byte in the regex', E_USER_ERROR);
    } elseif (strpos('\^$.[]|()?*+{}-/', $c) !== false) {
        return "\\".$c;
    } else {
        return $c;
    }
}

// recursively converts ERE into PCRE, starting at the position $i.
function _ere2pcre($s, $i) {
    $r = array('');
    $rr = 0;
    $l = strlen($s);

    while ($i < $l) {
        // atom
        $c = $s[$i];
        if ($c == '(') {
            if ($i + 1 < $l && $s[$i+1] == ')') { // special case
                $r[$rr] .= '()';
                ++$i;
            } else {
                list($t, $ii) = _ere2pcre($s, $i + 1);
                if ($ii >= $l || $s[$ii] != ')') {
                    trigger_error('ere2pcre: "(" does not have a matching ")"',
                                  E_USER_ERROR);
                }
                $r[$rr] .= '('.$t.')';
                $i = $ii;
            }
        } elseif ($c == '[') {
            ++$i;
            $cls = '';
            if ($i < $l && $s[$i] == '^') {
                $cls .= '^';
                ++$i;
            }
            if ($i >= $l) {
                trigger_error('ere2pcre: "[" does not have a matching "]"',
                              E_USER_ERROR);
            }
            $start = true;
            do {
                if ($s[$i] == '[' &&
                        $i+1 < $l && strpos('.=:', $s[$i+1]) !== false) {
                    $ii = strpos($s, ']', $i);
                    if ($ii === false) {
                        trigger_error('ere2pcre: "[" does not have a matching '.
                                      '"]"', E_USER_ERROR);
                    }
                    $ccls = substr($s, $i+1, $ii-($i+1));
                    $cclsmap = array(
                        ':alnum:' => '[:alnum:]',
                        ':alpha:' => '[:alpha:]',
                        ':blank:' => '[:blank:]',
                        ':cntrl:' => '[:cntrl:]',
                        ':digit:' => '\d',
                        ':graph:' => '[:graph:]',
                        ':lower:' => '[:lower:]',
                        ':print:' => '[:print:]',
                        ':punct:' => '[:punct:]',
                        ':space:' => '\013\s', // should include VT
                        ':upper:' => '[:upper:]',
                        ':xdigit:' => '[:xdigit:]',
                    );
                    if (!isset($cclsmap[$ccls])) {
                        trigger_error('ere2pcre: an invalid or unsupported '.
                                      'character class ['.$ccls.']',
                                      E_USER_ERROR);
                    }
                    $cls .= $cclsmap[$ccls];
                    $i = $ii + 1;
                } else {
                    $a = $s[$i++];
                    if ($a === '-' && !$start && !($i < $l && $s[$i] == ']')) {
                        trigger_error('ere2pcre: "-" is invalid for the start '.
                                      'character in the brackets',
                                      E_USER_ERROR);
                    }
                    if ($i < $l && $s[$i] === '-') {
                        ++$i;
                        $b = $s[$i++];
                        if ($b == ']') {
                            $cls .= _ere2pcre_escape($a).'\-';
                            break;
                        } elseif (ord($a) > ord($b)) {
                            trigger_error('ere2pcre: an invalid character '.
                                          'range "'.$a.'-'.$b.'"',
                                          E_USER_ERROR);
                        }
                        $cls .= _ere2pcre_escape($a).'-'._ere2pcre_escape($b);
                    } else {
                        $cls .= _ere2pcre_escape($a);
                    }
                }
                $start = false;
            } while ($i < $l && $s[$i] != ']');
            if ($i >= $l) {
                trigger_error('ere2pcre: "[" does not have a matching "]"',
                              E_USER_ERROR);
            }
            $r[$rr] .= '['.$cls.']';
        } elseif ($c == ')') {
            break;
        } elseif ($c == '*' || $c == '+' || $c == '?') {
            trigger_error('ere2pcre: unescaped metacharacter "'.$c.'"',
                          E_USER_ERROR);
        } elseif ($c == '{') {
            if ($i + 1 < $l && strpos('0123456789', $s[$i+1]) !== false) {
                $r[$rr] .= '\{';
            } else {
                trigger_error('ere2pcre: unescaped metacharacter "'.$c.'"',
                              E_USER_ERROR);
            }
        } elseif ($c == '.') {
            $r[$rr] .= $c;
        } elseif ($c == '^' || $c == '$') {
            $r[$rr] .= $c;
            ++$i;
            continue;
        } elseif ($c == '|') {
            if ($r[$rr] === '') {
                trigger_error('ere2pcre: empty branch', E_USER_ERROR);
            }
            $r[] = '';
            ++$rr;
            ++$i;
            continue;
        } elseif ($c == "\\") {
            if (++$i >= $l) {
                trigger_error('ere2pcre: an invalid escape sequence at the end',
                              E_USER_ERROR);
            }
            $r[$rr] .= _ere2pcre_escape($s[$i]);
        } else { // including ] and } which are allowed as a literal character
            $r[$rr] .= _ere2pcre_escape($c);
        }

        ++$i;
        if ($i >= $l) break;

        // piece after the atom (only ONE of them is possible)
        $c = $s[$i];
        if ($c == '*' || $c == '+' || $c == '?') {
            $r[$rr] .= $c;
            ++$i;
        } elseif ($c == '{') {
            $ii = strpos($s, '}', $i);
            if ($ii === false) {
                trigger_error('ere2pcre: "{" does not have a matching "}"',
                              E_USER_ERROR);
            }
            $bound = substr($s, $i+1, $ii-($i+1));
            if (!preg_match('/^([0-9]|[1-9][0-9]|1[0-9][0-9]|
                                2[0-4][0-9]|25[0-5])
                               (,([0-9]|[1-9][0-9]|1[0-9][0-9]|
                                  2[0-4][0-9]|25[0-5])?)?$/x',
                            $bound, $m)) {
                trigger_error('ere2pcre: an invalid bound', E_USER_ERROR);
            }
            if (isset($m[3])) {
                if ($m[1] > $m[3]) {
                    trigger_error('ere2pcre: an invalid bound', E_USER_ERROR);
                }
                $r[$rr] .= '{'.$m[1].','.$m[3].'}';
            } elseif (isset($m[2])) {
                $r[$rr] .= '{'.$m[1].',}';
            } else {
                $r[$rr] .= '{'.$m[1].'}';
            }
            $i = $ii + 1;
        }
    }
    if ($r[$rr] === '') {
        trigger_error('ere2pcre: empty regular expression or branch',
                      E_USER_ERROR);
    }
    return array(implode('|', $r), $i);
}

// converts the ERE $s into the PCRE $r. triggers error on any invalid input.
function ere2pcre($s, $ignorecase) {
    static $cache = array(), $icache = array();
    if ($ignorecase) {
        if (isset($icache[$s])) return $icache[$s];
    } else {
        if (isset($cache[$s])) return $cache[$s];
    }

    list($r, $i) = _ere2pcre($s, 0);
    if ($i != strlen($s)) {
        trigger_error('ere2pcre: unescaped metacharacter ")"', E_USER_ERROR);
    }
    if ($ignorecase) {
        return ($icache[$s] = '/'.$r.'/mi');
    } else {
        return ($cache[$s] = '/'.$r.'/m');
    }
}


// drop-in replacement for ereg.
function myereg($r, $s, &$m = null) {
    $r = ere2pcre($r, false);
    if (func_num_args() > 2) { // fix the result
        return (preg_match($r, $s, $m) ? strlen($m[0]) : false);
    } else {
        return (preg_match($r, $s) ? 1 : false);
    }
}

// drop-in replacement for eregi.
function myeregi($r, $s, &$m = null) {
    $r = ere2pcre($r, true);
    if (func_num_args() > 2) { // fix the result
        return (preg_match($r, $s, $m) ? strlen($m[0]) : false);
    } else {
        return (preg_match($r, $s) ? 1 : false);
    }
}

// drop-in replacement for ereg_replace.
function myereg_replace($r, $t, $s) {
    return preg_replace(ere2pcre($r, false), $t, $s);
}

// drop-in replacement for eregi_replace.
function myeregi_replace($r, $t, $s) {
    return preg_replace(ere2pcre($r, true), $t, $s);
}

// drop-in replacement for split.
function mysplit($r, $s, $l=-1) {
    return preg_split(ere2pcre($r, false), $s, ($l == 0 ? 1 : $l));
}

// drop-in replacement for spliti.
function myspliti($r, $s, $l=-1) {
    return preg_split(ere2pcre($r, true), $s, ($l == 0 ? 1 : $l));
}


// some test cases.
function ere2pcre_test() {
    foreach (array(
            'mearie.org',
            'mearie\.org',
            'mearie[.,]org',
            '[a-z]+[.,][a-z]+',
            '^[a-z]+[.,][a-z]+$',
            '^[a-z]+[.,][a-z]{3,}$',
            'a|b|(c|d)|e',
            'a|b|()|c',
            '[[:alnum:][:punct:]]',
            '[]-z]',
            '[[a]]',
            '[---]',
            '[a\z]',
            '[^^]',
            '^$^$^$^$',
            '\([^>]*\"?[^)]*\)',
            ) as $r) {
        printf("%-40s%-40s\n", $r, ere2pcre($r, false));
    }
    
    $r = "^(http(s?):\/\/|ftp:\/\/)*([[:alpha:]][-[:alnum:]]*[[:alnum:]])".
         "(\.[[:alpha:]][-[:alnum:]]*[[:alpha:]])+(/[[:alpha:]][-[:alnum:]]*".
         "[[:alnum:]])*(\/?)(/[[:alpha:]][-[:alnum:]]*\.[[:alpha:]]{3,5})?".
         "(\?([[:alnum:]][-_%[:alnum:]]*=[-_%[:alnum:]]+)(&([[:alnum:]]".
         "[-_%[:alnum:]]*=[-_%[:alnum:]]+))*)?$";
    printf("%s\n%s\n", $r, ere2pcre($r, false));
}