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bradleykirby bradleykirby is offline

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Regular Expression

Mar 13th, 2008

Hi, new to Perl. Learning regular expressions. Im trying to validate a form field using regular expressions. Field criteria is:

- Begin with a letter
- 4-8 characters long
- must include at least 1 digit

So far Ive got:

 Help with Code Tags 
 Perl Syntax (Toggle Plain Text) 
$fieldValid=$username=~/^\D\w{3,7}\d+/;
$fieldValid=$username=~/^\D\w{3,7}\d+/;

I read this as "beginning with any non-digit [^0-9], containing between 3 and 7 alphanumeric characters and having one or more of the previous character which is any digit"

I dont understand it, but \w{3,7} seems to satisfy having 4-8 alphanumeric long?
The following test usernames fall over:

a1bcdefg
ab1cdefg
abc1defg

The following are accepted:

abcd1efg
abcd1efg
abcdef1g
abcdefg1

So the location of the digit seems to be a factor, but not sure why.

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trudge

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Re: Regular Expression

Mar 14th, 2008

You may have to define 'character' a little better for your purposes. (Will you allow *?!@#$%^&()<>:;'~`)?

But the following works, while a bit kludgy:

 Help with Code Tags 
 Perl Syntax (Toggle Plain Text) 
#! /usr/bin/perl
use strict;
use warnings;
 
# Begin with a letter
# 4-8 characters long
# must include at least 1 digit
 
while (<DATA>)
{
	chomp;
	if ( (length($_) >= 4) && (length($_) <= 8) )
	{
		if ( /^[a-z]/)
		{
			if ( /\d+/g)
			{
				print "$_ : OK\n" ;
			}
		}
	}
	else
	{
		print "$_ : NO\n";
	}
}
 
__DATA__
1ab
abc
a1b
ab1
abc1
1abc
a1bc
ab1c
1a1bcdefg
a1bcdefg
ab1cdefg
abc1defg
abcd1efg
abcd1efg
abcdef1g
abcdefg1
a1234567
12345678
123456789
abcdefgh
abcdefghi
#! /usr/bin/perl
use strict;
use warnings;

# Begin with a letter
# 4-8 characters long
# must include at least 1 digit

while (<DATA>)
{
	chomp;
	if ( (length($_) >= 4) && (length($_) <= 8) )
	{
		if ( /^[a-z]/)
		{
			if ( /\d+/g)
			{
				print "$_ : OK\n" ;
			}
		}
	}
	else
	{
		print "$_ : NO\n";
	}
}

__DATA__
1ab
abc
a1b
ab1
abc1
1abc
a1bc
ab1c
1a1bcdefg
a1bcdefg
ab1cdefg
abc1defg
abcd1efg
abcd1efg
abcdef1g
abcdefg1
a1234567
12345678
123456789
abcdefgh
abcdefghi

Amer Neely - Web Mechanic
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Join Date: Mar 2006

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KevinADC

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Re: Regular Expression

Mar 14th, 2008

/^\D\w{3,7}\d+/;

the above means:

^\D starts with one non-digit character
\w{3,7} followed by 3 to 7 word characters, same as a-zA-Z0-9_
\d+ followed by one or more digits

what you probably want is is two regexps:

/\d/ has at least one digit

/^[a-zA-Z][a-zA-Z0-9]{3,7}/;

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bradleykirby bradleykirby is offline

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Re: Regular Expression

Mar 14th, 2008

Not sure how to use two regexps. Can you put them in the same statement like so:

 Help with Code Tags 
 Perl Syntax (Toggle Plain Text) 
$fieldValid=$username=~/^[a-zA-Z][a-zA-Z0-9]{3,7}/ && /\d/;
$fieldValid=$username=~/^[a-zA-Z][a-zA-Z0-9]{3,7}/ && /\d/;

or would I have to use a while loop, something like:

 Help with Code Tags 
 Perl Syntax (Toggle Plain Text) 
 
$formValid=1;
while ($username=~/\d/){
     	$fieldValid=$username=~/^[a-zA-Z][a-zA-Z0-9]{3,7}/;
        unless ($fieldValid)
        {$formValid=0
         }
}$formValid=0;
$formValid=1;
while ($username=~/\d/){
     	$fieldValid=$username=~/^[a-zA-Z][a-zA-Z0-9]{3,7}/;
        unless ($fieldValid)
        {$formValid=0
         }
}$formValid=0;

Which I read as "while there is a digit in $username, test the regular expression which if satisfied returns $fieldValid = true. If not satisfied, $fieldValid = false. Unless $fieldValid is true, then set $formValid = 0. If there is NOT a digit in $userName, then set $formValid = 0".

If the second way works, it sounds like a long winded way of doing it.

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KevinADC

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Re: Regular Expression

Mar 15th, 2008

 Help with Code Tags 
 Perl Syntax (Toggle Plain Text) 
if ($username =~ /\d/ &&  $username =~ /^[a-zA-Z][a-zA-Z0-9]{3,7}/) {
   $username is good do whatever you want
}
else {
   $username is bad
}
if ($username =~ /\d/ &&  $username =~ /^[a-zA-Z][a-zA-Z0-9]{3,7}/) {
   $username is good do whatever you want
}
else {
   $username is bad
}

But that might still not be good enough. The above will match strings like:

a1111111111111111111111111111111111111111111111111111111111111.....

if you need to match a specific length you have to add the end of string anchor ($) to the second regexp:

 Help with Code Tags 
 Perl Syntax (Toggle Plain Text) 
if ($username =~ /\d/ &&  $username =~ /^[a-zA-Z][a-zA-Z0-9]{3,7}$/) {
   $username is good do whatever you want
}
else {
   $username is bad
}
if ($username =~ /\d/ &&  $username =~ /^[a-zA-Z][a-zA-Z0-9]{3,7}$/) {
   $username is good do whatever you want
}
else {
   $username is bad
}

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jephthah

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Re: Regular Expression

Mar 16th, 2008

you could do something like

 Help with Code Tags 
 perl Syntax (Toggle Plain Text) 
if (str =~ /^[a-z](?:\d\w{2,6}|\w{2,6}\d|\w\d\w{1,5}|\w{2}\d\w{0,4}|\w{3}\d\w{0,3}|\w{4}\d\w{0,2}|\w{5}\d\w?)$/i)
{
     ... stuff ...
}
if (str =~ /^[a-z](?:\d\w{2,6}|\w{2,6}\d|\w\d\w{1,5}|\w{2}\d\w{0,4}|\w{3}\d\w{0,3}|\w{4}\d\w{0,2}|\w{5}\d\w?)$/i)
{
     ... stuff ...
}

but i would rather

 Help with Code Tags 
 perl Syntax (Toggle Plain Text) 
if (str =~ /^[a-z](\w{3,7})/ )
{
    if ($1 =! /\d/ || $1 =! /[A-Z]/ || $1 != /[a-z]/)
    { 
        die "must have one number, cap, and lowercase!\n";
    }
 
    ... stuff ...
}
if (str =~ /^[a-z](\w{3,7})/ )
{
    if ($1 =! /\d/ || $1 =! /[A-Z]/ || $1 != /[a-z]/)
    { 
        die "must have one number, cap, and lowercase!\n";
    }

    ... stuff ...
}

Last edited by jephthah; Mar 16th, 2008 at 7:19 pm.

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jephthah

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Re: Regular Expression

Mar 17th, 2008

hmm.... my long regex above is cut off by the webcode formatting.

that's kind of crappy. and all that after everyone bitches about people not using the webcode tags

anyhow, you'll have to click the "toggle plain text" to see it.

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Narue

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Re: Regular Expression

Mar 17th, 2008

>that's kind of crappy.
Yes, it is. You should take advantage of the /x modifier.

I'm here to prove you wrong.

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bradleykirby bradleykirby is offline

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Re: Regular Expression

Mar 17th, 2008

Hi guys, thanks for all your responses. Think I found what I was after, all in one regex.

The one offered by jephthah allows non-letters at the start, so &? etc allowed.

I managed to use a condensed regex using a lookahead:

 Help with Code Tags 
 Perl Syntax (Toggle Plain Text) 
/(?=^[a-zA-Z0-9]{4,8}$)[a-zA-Z][a-zA-Z0-9]{0,2}\d+/
/(?=^[a-zA-Z0-9]{4,8}$)[a-zA-Z][a-zA-Z0-9]{0,2}\d+/

Curious about the /x modifier tho, because I have another regex thats taking up about two page widths - is /x a way to split your code over 2 or more lines?

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jephthah

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Re: Regular Expression

#10

Mar 17th, 2008

•

Originally Posted by bradleykirby

The one offered by jephthah allows non-letters at the start, so &? etc allowed.

what are you talking about? it does not in any sense allow non letters at the start, or anywhere else for that matter ... it will allow the underscore "_" in any position other than the first, which is typically allowed (and desired) anywhere alphanumerics are allowed.

and i'm afraid to tell you, your last attempt won't work at all, for anything. maybe mine ain't pretty, but it works.

•

Curious about the /x modifier tho, because I have another regex thats taking up about two page widths - is /x a way to split your code over 2 or more lines?

yeah, narue just busted me. it means "ignore whitespace" ... so you can put a CR/LF in there for readability.

Last edited by jephthah; Mar 17th, 2008 at 2:49 pm.