This is very inadvisable. But if you're not a programmer, or really prefer terrible code, you could use a substitute preg_replace
function to keep your /e
flag working temporarily.
/**
* Can be used as a stopgap shim for preg_replace() calls with /e flag.
* Is likely to fail for more complex string munging expressions. And
* very obviously won't help with local-scope variable expressions.
*
* @license: CC-BY-*.*-comment-must-be-retained
* @security: Provides `eval` support for replacement patterns. Which
* poses troubles for user-supplied input when paired with overly
* generic placeholders. This variant is only slightly stricter than
* the C implementation, but still susceptible to varexpression, quote
* breakouts and mundane exploits from unquoted capture placeholders.
* @url: https://stackoverflow.com/q/15454220
*/
function preg_replace_eval($pattern, $replacement, $subject, $limit=-1) {
# strip /e flag
$pattern = preg_replace('/(\W[a-df-z]*)e([a-df-z]*)$/i', '$1$2', $pattern);
# warn about most blatant misuses at least
if (preg_match('/\(\.[+*]/', $pattern)) {
trigger_error("preg_replace_eval(): regex contains (.*) or (.+) placeholders, which easily causes security issues for unconstrained/user input in the replacement expression. Transform your code to use preg_replace_callback() with a sane replacement callback!");
}
# run preg_replace with eval-callback
return preg_replace_callback(
$pattern,
function ($matches) use ($replacement) {
# substitute $1/$2/… with literals from $matches[]
$repl = preg_replace_callback(
'/(?<!\\\\)(?:[$]|\\\\)(\d+)/',
function ($m) use ($matches) {
if (!isset($matches[$m[1]])) { trigger_error("No capture group for '$m[0]' eval placeholder"); }
return addcslashes($matches[$m[1]], '\"\'\`\$\\\0'); # additionally escapes '$' and backticks
},
$replacement
);
# run the replacement expression
return eval("return $repl;");
},
$subject,
$limit
);
}
In essence, you just include that function in your codebase, and edit preg_replace
to preg_replace_eval
wherever the /e
flag was used.
Pros and cons:
preg_replace_callback
.Now this is somewhat redundant. But might help those users who are still overwhelmed
with manually restructuring their code to preg_replace_callback
. While this is effectively more time consuming, a code generator has less trouble to expand the /e
replacement string into an expression. It's a very unremarkable conversion, but likely suffices for the most prevalent examples.
To use this function, edit any broken preg_replace
call into preg_replace_eval_replacement
and run it once. This will print out the according preg_replace_callback
block to be used in its place.
/**
* Use once to generate a crude preg_replace_callback() substitution. Might often
* require additional changes in the `return …;` expression. You'll also have to
* refit the variable names for input/output obviously.
*
* >>> preg_replace_eval_replacement("/\w+/", 'strtopupper("$1")', $ignored);
*/
function preg_replace_eval_replacement($pattern, $replacement, $subjectvar="IGNORED") {
$pattern = preg_replace('/(\W[a-df-z]*)e([a-df-z]*)$/i', '$1$2', $pattern);
$replacement = preg_replace_callback('/[\'\"]?(?<!\\\\)(?:[$]|\\\\)(\d+)[\'\"]?/', function ($m) { return "\$m[{$m[1]}]"; }, $replacement);
$ve = "var_export";
$bt = debug_backtrace(0, 1)[0];
print "<pre><code>
#----------------------------------------------------
# replace preg_*() call in '$bt[file]' line $bt[line] with:
#----------------------------------------------------
\$OUTPUT_VAR = preg_replace_callback(
{$ve($pattern, TRUE)},
function (\$m) {
return {$replacement};
},
\$YOUR_INPUT_VARIABLE_GOES_HERE
)
#----------------------------------------------------
</code></pre>\n";
}
Take in mind that mere copy&pasting is not programming. You'll have to adapt the generated code back to your actual input/output variable names, or usage context.
$OUTPUT =
assignment would have to go if the previous preg_replace
call was used in an if
.And the replacement expression may demand more readability improvements or rework.
stripslashes()
often becomes redundant in literal expressions.use
or global
reference for/within the callback."-$1-$2"
capture references will end up syntactically broken by the plain transformation into "-$m[1]-$m[2]
.The code output is merely a starting point. And yes, this would have been more useful as an online tool. This code rewriting approach (edit, run, edit, edit) is somewhat impractical. Yet could be more approachable to those who are accustomed to task-centric coding (more steps, more uncoveries). So this alternative might curb a few more duplicate questions.