PHP - Regex : I need help to build regex according these rules

Question

I need help building a regular expression for preg_match according these rules:

first and last char- letter/digit only.
empty space not allowed
char can be only - letter/digit/'-'/'_'/'.'

Legal examples:

b.t612_rt
rut-be
rut7565

Not legal example:

.btr78; btr78- (first/last allowed chars)
start end; star t end; (any empty space)
tr$be; tr*rt; tr/tr ... (not allowed chars)

Edit: I remove 4 rule with neigbor chars '_'\'-'\'.'

please help me.

Thanks

Why don't you try writing one yourself, and we can help you if it doesn't work as intended? You'll never learn anything if you ask others to do all your work for you without even attempting it first. — user229044
– user229044 ♦, Commented Feb 2, 2011 at 14:36
Open-source alternatives to RegexBuddy lists a few nice tools to help with constructing a regular expression. — mario
– mario, Commented Feb 2, 2011 at 14:45

Gumbo · Accepted Answer · 2011-02-02 14:44:46Z

3

Try this regular expression:

^[A-Za-z0-9]+([-_.][A-Za-z0-9]+)*$

This matches any sequence that starts with at least one letter or digit (^[A-Za-z0-9]+) that may be followed by zero or more sequences of one of -, _, or . ([-_.]) that must be followed by at least one letter or digit ([A-Za-z0-9]+).

edited Feb 2, 2011 at 14:44

answered Feb 2, 2011 at 14:39

Gumbo

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2 Comments

user229044 Over a year ago

+1 for simplest solution without a bunch of look-ahead stuff.

Gumbo Over a year ago

@dani: Then replace [-_.] by [-_.]+.

Tim Pietzcker · Accepted Answer · 2011-02-02 15:00:07Z

2

Try this:

^[\p{L}\p{N}][\p{L}\p{N}_.-]*[\p{L}\p{N}]$

In PHP:

if (preg_match(
    '%^               # start of string
    [\p{L}\p{N}]      # letter or digit
    [\p{L}\p{N}_.-]*  # any number of letters/digits/-_.
    [\p{L}\p{N}]      # letter or digit
    $                 # end of the string.
    %xu', 
    $subject)) {
    # Successful match
} else {
    # Match attempt failed
}

Minimum string length: Two characters.

edited Feb 2, 2011 at 15:00

answered Feb 2, 2011 at 14:39

Tim Pietzcker

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Comments

mateusza · Accepted Answer · 2011-02-02 14:46:27Z

1

This seems to work fine for provided examples: $patt = '/^[a-zA-Z0-9]+([-._][a-zA-Z0-9]+)*$/';

answered Feb 2, 2011 at 14:46

mateusza

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Comments

ircmaxell · Accepted Answer · 2011-02-02 14:46:38Z

1

Well, for each of your rules:

First and last letter/digit:
```
^[a-z0-9]
```
and
```
[a-z0-9]$
```
empty space not allowed (nothing is needed, since we're doing a positive match and don't allow any whitespace anywhere):
Only letters/digits/-/_/.
```
[a-z0-9_.-]*
```
No neighboring symbols:
```
(?!.*[_.-][_.-])
```

So, all together:

/^[a-z0-9](?!.*[_.-][_.-])[a-z0-9_.-]*[a-z0-9]$/i

But with all regexes, there are multiple solutions, so try it out...

Edit: for your edit:

/^[a-z0-9][a-z0-9_.-]*[a-z0-9]$/i

You just remove the section for the rule you want to change/remote. it's that easy...

edited Feb 2, 2011 at 14:46

answered Feb 2, 2011 at 14:40

ircmaxell

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1 Comment

ircmaxell Over a year ago

@meagar: fixed, I didn't add the any character match to the forward assertion. It should work now

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