Simple regex pattern in PHP

Question

I need to match the first few characters of a string. The match is true if:

The first character is a letter (case insensitive)
The second character is either a digit or a letter
If the second character is a digit, the match is returned true
If the second character is a letter, the third character must be a digit
The pattern will ignore all other subsequent characters in the string

Examples:

AB1ghRjh  //true
c1        //true
G44       //true
Tt7688    //true
kGF98d    //false
4FG3      //false
4 5a      //false
RRFDE     //false

Would appreciate if anyone could supply an example.

Thanks a lot!

This may be a beginner question, but it is clear and has a good answer. — user3956566
– user3956566, Commented Jul 6, 2018 at 9:53

Anirudha · Accepted Answer · 2013-10-29 06:47:34Z

2

Regex would be

^[a-zA-Z](\d|[a-zA-Z]\d).*

answered Oct 29, 2013 at 6:47

Anirudha

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revo · Accepted Answer · 2013-10-29 07:46:34Z

1

/^(?:[a-z]{2}|[a-z])\d.*$/im

Explanation:

^   # Start of string
    (?: # Start non-capturing group
        [a-z]{2}    # Two letter
        |   # OR
        [a-z]   # One letter
    )   # End of non-capturing group
    \d  # At least a digit here
    .*  # Escape all other characters
$   # End of string

i flag means case insensitive, m flag means make ^ & $ do matching on each line (optional if your input hasn't newlines)

Live demo

Then using preg_match function to match the strings:

if(preg_match("/^(?:[a-z]{2}|[a-z])\d.*$/i", "AB1ghRjh"))
{
    echo "Matched";
}

edited Oct 29, 2013 at 7:46

answered Oct 29, 2013 at 7:37

revo

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2 Comments

R C Over a year ago

Wow - thanks to all replies, but especially to yours for taking the time to explain it all out and for including a sample PHP statement. Really appreciate it!!!

revo Over a year ago

After 5 years I could see that the regex in this answer is somehow wordy. Someone could write ^[a-z]{1,2}\d instead with i flag enabled.

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