Enabling preg_replace_callback() replacement function if it's loaded from string

Question

I have input strings like

Wires: 8 Pairs: 4

The both numbers may be different for different strings

So, only dividing and only numbers can be different

I need to get the output result like

Wires: 2 Pairs: 4

That is the number of wires should become the result of diving the first number by the second one

Here is my working PHP code:

<?php
$input = 'Wires: 8 Pairs: 4';
$pattern = '(Wires:)(\s)(\d+)(\s)(Pairs:)(\s)(\d+)';

$output = preg_replace_callback('/'.$pattern.'/',
    function($m) {
        return 'Wires: '.$m[3]/$m[7].' Pairs: '.$m[7];
    },
$input);

echo $output;

But the point is, both patterns and replacements should be stored in and loaded from external JSON file as strings.

The patterns are working if I store them in the file, adding two escaping backslashes instead of one like (\\s)(\\d+)

But how to deal with the replacements?

If I try something like

<?php
$input = 'Wires: 8 Pairs: 4';
$pattern = '(Wires:)(\s)(\d+)(\s)(Pairs:)(\s)(\d+)';
$replacement = 'Wires: $m[3]/$m[7] Pairs: $m[3]';

$output = preg_replace_callback('/'.$pattern.'/',
    function($m) {
        global $replacement;
        return $replacement;
    },
$input);

echo $output;

I simply get

Wires: $m[3]/$m[7] Pairs: $m[3]

What if you go with "Wires: {$m[3]}/{$m[7]} Pairs: {$m[3]}"? — Randommm
– Randommm, Commented May 4, 2023 at 11:52
We only have one primitive example. How dynamic does this need to be? Are you ever doing more than dividing two numbers? This design decision has a smell and may need a rethink. Please edit your question to better express how the input may vary. — mickmackusa
– mickmackusa ♦, Commented May 4, 2023 at 12:41
@mickmackusa Only dividing. And only numbers can be different — stckvrw
– stckvrw, Commented May 4, 2023 at 12:42
So the Wires and Pairs is consistent in the input strings? — mickmackusa
– mickmackusa ♦, Commented May 4, 2023 at 12:50

shingo · Accepted Answer · 2023-05-04 12:36:35Z

1

PHP doesn't allow you to serialize functions, so to serialize a function, you need a library such as this one: https://github.com/opis/closure

If using a library cannot be your choice, another convenient but VERY DANGEROUS way is to use eval.

$repl = 'return "Wires: ".$m[3]/$m[7]." Pairs: ".$m[7];';

$output = preg_replace_callback('/'.$pattern.'/',
    function($m) use ($repl) {
        return eval($repl);
    },
$input);

edited May 4, 2023 at 12:36

answered May 4, 2023 at 12:24

shingo

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2 Comments

stckvrw Over a year ago

shingo, you missed global $repl Without it I get "Undefined variable $repl"

shingo Over a year ago

@stckvrw I‘ve corrected it.

mickmackusa · Accepted Answer · 2023-05-04 13:05:00Z

1

There is absolutely no reason to store any part of this task anywhere else because you state that only the numbers will change.

Use sprintf() to avoid quoting problems.

Code: (Demo)

$input = 'Wires: 8 Pairs: 4';
echo preg_replace_callback(
         '/Wires: (\d+) Pairs: (\d+)/',
         fn($m) => sprintf(
                 'Wires: %d Pairs: %d',
                 $m[1] / $m[2],
                 $m[2]
             ),
         $input
     );

Or, you can use sscanf() and printf(). Demo

sscanf($input, 'Wires: %d Pairs: %d', $wires, $pairs);
printf('Wires: %d Pairs: %d', $wires / $pairs, $pairs);

edited May 4, 2023 at 13:05

answered May 4, 2023 at 12:33

mickmackusa♦

49.2k13 gold badges98 silver badges165 bronze badges

5 Comments

mighty_dev Over a year ago

both patterns and replacements should be stored in and loaded from external JSON file as strings. So I presume you can't manually write the math on our own.

stckvrw Over a year ago

mickmackusa thanks, but I need the replacement prepared outside the preg_replace_callback(). It's not a problem for me to manually write it inside

mickmackusa Over a year ago

Why do you believe that you require the replacement to be declared somewhere else? It is either a bad idea or you need to explain the reason for this complexity.

stckvrw Over a year ago

@mickmackusa There are also another patterns and replacements in JSON file for preg_replace(). But yes, you're right - I can just store there numbers for my preg_replace_callback()

mickmackusa Over a year ago

I suppose you could do something like 3v4l.org/I7iXq, but I don't see the benefit.

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