modify string if specific regex matches

Question

Working in PHP, I have the following mock string.

"width 40cm height 70cm"

If the string does not contain a colon and does have a space followed by a number, I want to add a colon before that space.

The end result I'm looking for is:

"width: 40cm height: 70cm"

I tried a bunch of ways with regex and splitting the string at the match to add the colon, but it was removing the match string. Here is my attempt.

    if(strpos($s, ':') === false) {
        $array = preg_split('/([0-9])/', $s, -1, PREG_SPLIT_NO_EMPTY);
        $array[0] = trim($array[0]) . ':';
        $s = implode('', $array);
    }

rock321987 · Accepted Answer · 2016-06-11 10:06:50Z

1

I think this will work

(\w+)(?=\s+\d)
     <------->
     Lookahead to match
     space followed by 
     digits

Regex Demo

PHP Code

$re = "/(\\w+)(?=\\s+\\d)/m"; 
$str = "width 40cm height 70cm\nwidth: 40cm height 70cm"; 

$result = preg_replace($re, "$1:", $str);
print_r($result);

Ideone Demo

edited Jun 11, 2016 at 10:06

answered Jun 11, 2016 at 7:57

rock321987

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2 Comments

Casimir et Hippolyte Over a year ago

No need to put a negative lookahead here: (?!:)\s, a white-space can't be a colon.

rock321987 Over a year ago

@CasimiretHippolyte you are right..my fault..i wrote the lookahead part in starting and then added the \w part and messed it up..

Andreas Louv · Accepted Answer · 2016-06-11 08:02:36Z

1

The following regex might work for you:

/(?<!:)(?= \d)/g

With replacement: :

$output = preg_replace('/(?<!:)(?= \d)/', ':', $input);

It matches a position that is followed before space and digit (?= \d) and not preceded by a colon (?<!:). That's why the replacement group can be a colon only.

This is called lookarounds. Here be both use a positive lookahead (?=...) and a negative lookbehind: (?<!...).

https://www.regex101.com/r/oH7cI3/1

edited Jun 11, 2016 at 8:02

answered Jun 11, 2016 at 7:57

Andreas Louv

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Comments

Jan · Accepted Answer · 2016-06-11 08:08:18Z

1

Use lookarounds:

(?<=[a-z]) # a-z behind
\          # a space
(?=\d)     # a digit ahead

See a demo on regex101.com and replace the occurences with a colon.

answered Jun 11, 2016 at 8:08

Jan

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Comments

abhijeet dbritto · Accepted Answer · 2016-06-11 07:58:58Z

0

$string="width: 40cm height: 70cm";

$temp=exploade(" ",$string);

foreach($temp as $value){

if(strstr($value,'width') && strstr($value,'height')){
    $new_temp[]=$value.":";
}else{
    $new_temp[]=$value;
}

} $new_string=implode(" ", $new_temp);

answered Jun 11, 2016 at 7:58

abhijeet dbritto

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