How to insert string after every fifth occurrence of another string?

Question

I want to insert string in certain position of character using PHP, so I have string like this:

$string = "
    <p>1</p>
    <p>2</p>
    <p>3</p>
    <p>4</p>
    <p>5</p>
    <p>6</p>
    <p>7</p>
    <p>8</p>
    <p>9</p>
    <p>10</p>
    <p>11</p>
    <p>12</p>
    <p>13</p>
    <p>14</p>
    <p>15</p>
    <p>16</p>
    <p>17</p>
    ";

I want to append this bb code [next] after every multiple of 5  tag, so it would be like this:

$string = "
    <p>1</p>
    <p>2</p>
    <p>3</p>
    <p>4</p>
    <p>5</p>
    [next] //appended bb code
    <p>6</p>
    <p>7</p>
    <p>8</p>
    <p>9</p>
    <p>10</p>
    [next] //appended bb code
    <p>11</p>
    <p>12</p>
    <p>13</p>
    <p>14</p>
    <p>15</p>
    [next] //appended bb code
    <p>16</p>
    <p>17</p>
    ";

I have a case that I have a post article that needs to paginate after the fifth , tenth , fifteenth  and so on. What I have tried is to find and get the number of position of each  and append the [next] bb code when at the tenth paragraph (). and that works well.

$string = "
    <p>1</p>
    <p>2</p>
    <p>3</p>
    <p>4</p>
    <p>5</p>
    <p>6</p>
    <p>7</p>
    <p>8</p>
    <p>9</p>
    <p>10</p>
    <p>11</p>
    <p>12</p>
    <p>13</p>
    <p>14</p>
    <p>15</p>
    <p>16</p>
    <p>17</p>
";
    $paginate = '[next]';
    $found = 0;
    
    for($i = 1; $i <= 99; $i++) {
        $paragraph = strpos($string, "</p>", $found);
        $found = $paragraph + 1;

        if ($i == 10) {
            $string = substr_replace($string, $paginate, $paragraph, 0);
        }
    }

    echo $string;

The Result (Output):

I'm struggling when I'm tried to append that bb code every multiple of 5  tag, so any help is much appreciated.

mickmackusa · Answer 1 · 2021-02-18T11:14:30.120

2

Match every everything up to the fifth  tag, then forget it all with \K, then inject your bbcode.

Code: (Demo)

echo preg_replace('~(?:.*?</p>){5}\K~s', "\n    [next]", $string);

If you want a tag-ignorant pattern, here is one:

~((^|\R).+){5}\K~

Or fully respecting your system's newline sequences:

echo preg_replace('~(?:.+\K\R){5}~', "$0    [next]$0", $string);

edited Feb 18 '21 at 11:14

answered Feb 18 '21 at 10:36

mickmackusa

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score 1 · Accepted Answer · answered Feb 18 '21 at 10:27

With some judisious use of explode() and implode() and th modulus % operator, you can do it this way

$string = 
"<p>1</p>
<p>2</p>
<p>3</p>
<p>4</p>
<p>5</p>
<p>6</p>
<p>7</p>
<p>8</p>
<p>9</p>
<p>10</p>
<p>11</p>
<p>12</p>
<p>13</p>
<p>14</p>
<p>15</p>
<p>16</p>
<p>17</p>
";
$paginate = '[next]';

$lines = explode("\n", $string);

foreach ($lines as $i => $line) {  
    if ($i != 0 && $i % 5 == 0) {
        $new[] = $paginate;
    }
    $new[] = $line;
}

$string = implode("\n", $new);
echo $string;

RESULT

<p>1</p>
<p>2</p>
<p>3</p>
<p>4</p>
<p>5</p>
[next]
<p>6</p>
<p>7</p>
<p>8</p>
<p>9</p>
<p>10</p>
[next]
<p>11</p>
<p>12</p>
<p>13</p>
<p>14</p>
<p>15</p>
[next]
<p>16</p>
<p>17</p>

How to insert string after every fifth occurrence of another string?

2 Answers2