Test if a string is equal to one of the strings (with regex)

Question

How could this be done with regex?

 return ( $s=='aa' || $s=='bb' || $s=='cc' || $s=='dd' ) ? 1 : 0;

I am trying:

 $s = 'aa';
 $result = preg_match( '/(aa|bb|cc|dd)/', $s );
 echo $result; // 1

but obviously this returns 1 if $s contains one or more of the specified strings (not when it is equal to one of them).

Avinash Raj · Accepted Answer · 2014-11-18 16:14:22Z

11

You need to use start ^ and end $ anchors to do an exact string match.

$result = preg_match( '/^(aa|bb|cc|dd)$/', $s );

answered Nov 18, 2014 at 16:14

Avinash Raj

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t.h3ads · Accepted Answer · 2014-11-18 16:15:15Z

3

$s = 'aa';
$result = preg_match( '/^(aa|bb|cc|dd)$/', $s );
echo $result;

Use ^ and $ to specify the to match from the beginning of the input till the end.

answered Nov 18, 2014 at 16:15

t.h3ads

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Comments

Adil · Accepted Answer · 2014-11-18 16:16:42Z

3

I think RegEx overkill for this problem.

My solution:

$results = array('aa', 'bb', 'cc', 'dd');
$c = 'aa';

if(in_array($c, $results, true)) {
    echo 'YES';
} else {
    echo 'NO';
}

answered Nov 18, 2014 at 16:16

Adil

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10 Comments

Leandro Bardelli Over a year ago

What it means "overkill" ? I'm not agree with you.

Styphon Over a year ago

The difference is negligible, you can use whichever you prefer - eval.in/223092

Adil Over a year ago

@Styphon, your comparison not equal. eval.in/private/81d6123d2cd184 - eval.in/private/481f2ed8552cb2

Styphon Over a year ago

@AdilIlhan Run them on the same script, eval.in will not give accurate results if they're on different pages. Each time you run it you will get a different result of up to 0.2s.

sanchez Over a year ago

Although I am not going to use this approach in this case, +1 for starting another interesting RegEx vs world micro optimisation battle.

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