I'm trying to create an s3 bucket through cloudformation. I tried using regex ^([0-9a-z.-]){3,63}$, but it also accepts the patterns "..." and "---" which are invalid according to new s3 naming conventions. (Ref: https://docs.aws.amazon.com/AmazonS3/latest/dev/BucketRestrictions.html) Please help?
Answer
The simplest and safest regex is:
(?!(^xn--|.+-s3alias$))^[a-z0-9][a-z0-9-]{1,61}[a-z0-9]$
It ensures that names work for all cases - including when you are using S3 Transfer Acceleration. Also, as it doesn't include any backslashes, it's easier to use in string contexts.
Alternative
If you need S3 bucket names that include dots (and you don't use S3 Transfer Acceleration), you can use this instead:
(?!(^((2(5[0-5]|[0-4][0-9])|[01]?[0-9]{1,2})\.){3}(2(5[0-5]|[0-4][0-9])|[01]?[0-9]{1,2})$|^xn--|.+-s3alias$))^[a-z0-9][a-z0-9.-]{1,61}[a-z0-9]$
Explanation
The Amazon S3 bucket naming rules as of 2022-05-14 are:
Bucket names must be between 3 (min) and 63 (max) characters long.
Bucket names can consist only of lowercase letters, numbers, dots (.), and hyphens (-).
Bucket names must begin and end with a letter or number.
Bucket names must not be formatted as an IP address (for example, 192.168.5.4).
Bucket names must not start with the prefix xn--.
Bucket names must not end with the suffix -s3alias.
Buckets used with Amazon S3 Transfer Acceleration can't have dots (.) in their names.
This regex matches all the rules (including rule 7):
(?!(^xn--|.+-s3alias$))^[a-z0-9][a-z0-9-]{1,61}[a-z0-9]$
The first group (?!(^xn--|-s3alias$)) is a negative lookahead that ensures that the name doesn't start with xn-- or end with -s3alias (satisfying rules 5 and 6).
The rest of the expression ^[a-z0-9][a-z0-9-]{1,61}[a-z0-9]$ ensures that:
the name starts with a lowercase letter or number (^[a-z0-9]) and ends with a lowercase letter or number ([a-z0-9]$) (rule 3).
the rest of the name consists of 1 to 61 lowercase letters, numbers or hyphens ([a-z0-9-]{1,61}) (rule 2).
the entire expression matches names from 3 to 63 characters in length (rule 1).
Lastly, we don't need to worry about rule 4 (which forbids names that look like IP addresses) because rule 7 implicitly covers this by forbidding dots in names.
If you do not use Amazon S3 Transfer Acceleration and want to permit more complex bucket names, then you can use this more complicated regular expression:
(?!(^((2(5[0-5]|[0-4][0-9])|[01]?[0-9]{1,2})\.){3}(2(5[0-5]|[0-4][0-9])|[01]?[0-9]{1,2})$|^xn--|.+-s3alias$))^[a-z0-9][a-z0-9.-]{1,61}[a-z0-9]$
The main change is the addition of the expression to match IPv4 addresses (while the spec simply says that bucket names must not be formatted as IP addresses, as IPv6 addresses contain colons, they are already forbidden by rule 2.)
The following regex fulfils the AWS specifications provided the fact you don't want to allow . in the bucket name (which is a recommendation, otherwise Transfer Acceleration can't be enabled):
^((?!xn--)(?!.*-s3alias$)[a-z0-9][a-z0-9-]{1,61}[a-z0-9])$
This one is good because it allows to be incorporated in more complex checks simply replacing ^ and $ with other strings, thus allowing for ARN checks and so on.
EDIT:
added -s3alias exclusion as per the comment by #ryanjdillon
I've adapted Zak's answer a little bit. I found it was a little too complicated and threw out valid domain names. Here's the new regex (available with tests on regex101.com**):
(?!^(\d{1,3}\.){3}\d{1,3}$)(^[a-z0-9]([a-z0-9-]*(\.[a-z0-9])?)*$)
The first part is the negative lookahead (?!^(\d{1,3}\.){3}\d{1,3}$), which only matches valid IP addresses. Basically, we try to match 1-3 numbers followed by a period 3 times (\d{1,3}\.){3}) followed by 1-3 numbers (\d{1,3}).
The second part says that the name must start with a lowercase letter or a number (^[a-z0-9]) followed by lowercase letters, numbers, or hyphens repeated 0 to many times ([a-z0-9-]*). If there is a period, it must be followed by a lowercase letter or number ((\.[a-z0-9])?). These last 2 patterns are repeated 0 to many times (([a-z0-9-]*(\.[a-z0-9])?)*).
The regex does not attempt to enforce the size restrictions set forth by AWS (3-63 characters). That can either be handled by another regex (.{3,6}) or by checking the size of the string.
** At that link, one of the tests I added are failing, but if you switch to the test area and type in the same pattern, it passes. It also works if you copy/paste it into the terminal, so I assume that's a bug on the regex101.com side.
Regular expression for S3 Bucket Name:
String S3_REPORT_NAME_PATTERN = "[0-9A-Za-z!\\-_.*\'()]+";
String S3_PREFIX_PATTERN = "[0-9A-Za-z!\\-_.*\\'()/]*";
String S3_BUCKET_PATTERN = "(?=^.{3,63}$)(?!^(\\d+\\.)+\\d+$)(^(([a-z0-9]|[a-z0-9][a-z0-9\\-]*[a-z0-9])\\.)*([a-z0-9]|[a-z0-9][a-z0-9\\-]*[a-z0-9])$)";
I used #Zak regex but it isn't 100% correct. I used this for all rules for AWS bucket name. I make validation step by step so it looks like this:
Bucket names must be at least 3 and no more than 63 characters long -> ^.{3,63}$
Bucket names must not contain uppercase characters or underscores -> [A-Z_]
Bucket names must start with a lowercase letter or number -> ^[a-z0-9]
Bucket names must not be formatted as an IP address (for example, 192.168.5.4) ->^(\d+\.)+\d+$. That is more restricted then AWS.
Bucket names must be a series of one or more labels. Adjacent labels are separated by a single period (.) -> In python if ".." in bucket_name:
.. Each label must end with a lowercase letter or a number ->^(.*[a-z0-9]\.)*.*[a-z0-9]$
var bucketRGEX = new RegExp(/(?=^.{3,63}$)/);
var bucketRGEX1 = new RegExp(/(?!^(\d+\.)+\d+$)/);
var bucketRGEX2 = new RegExp(/(^(([a-z0-9]|[a-z0-9][a-z0-9\-]*[a-z0-9])\.)*([a-z0-9]|[a-z0-9][a-z0-9\-]*[a-z0-9])$)/);
var result = bucketRGEX.test(bucketName);
var result1 = bucketRGEX1.test(bucketName);
var result2 = bucketRGEX2.test(bucketName);
console.log('bucketName '+bucketName +' result '+result);
console.log('bucketName '+bucketName +' result1 '+result1);
console.log('bucketName '+bucketName +' result 2 '+result2);
if(result && result1 && result2)
{
//condition pass
}
else
{
//not valid bucket name
}
AWS issued new guidelines where '.' is considered not recommended and bucket names starting with 'xn--' are now prohibited (https://docs.aws.amazon.com/AmazonS3/latest/dev/BucketRestrictions.html). If you disallow '.' the regex becomes much more readable:
(?=^.{3,63}$)(?!xn--)([a-z0-9](?:[a-z0-9-]*)[a-z0-9])$
I tried passing a wrong bucket name to the S3 API itself to see how it validates. Looks like the following are valid regex patterns as returned in the API response.
Bucket name must match the regex
^[a-zA-Z0-9.\-_]{1,255}$
or be an ARN matching the regex
^arn:(aws).*:(s3|s3-object-lambda):[a-z\-0-9]+:[0-9]{12}:accesspoint[/:][a-zA-Z0-9\-]{1,63}$|^arn:(aws).*:s3-outposts:[a-z\-0-9]+:[0-9]{12}:outpost[/:][a-zA-Z0-9\-]{1,63}[/:]accesspoint[/:][a-zA-Z0-9\-]{1,63}$
Edit: Modified the regexp to allow required size (3-63) and add some other options.
The names must be DNS-compliant, so you could try with:
^[A-Za-z0-9][A-Za-z0-9\-]{1,61}[A-Za-z0-9]$
See: https://regexr.com/3psne
Use this if you need to use periods:
^[A-Za-z0-9][A-Za-z0-9\-.]{1,61}[A-Za-z0-9]$
See: https://regexr.com/3psnb
Finally, if you want to disallow two consecutive 'non-word' characters, you can use:
^[A-Za-z0-9](?!.*[.-]{2})[A-Za-z0-9\-.]{1,61}[A-Za-z0-9]$
See: https://regexr.com/3psn8
Based on: Regexp for subdomain
If you do not use transfer accelration, you can simply remove the period option. This code accounts for all the rules, including
no double dots
no slash/doto combo in a ow
no dot/slash combo
it also allows for you to put a trailing slash at the bucket name or not, depending if you want your user to do so
(?!^|xn--)[a-z0-9]{1}[a-z0-9-.]{1,61}[a-z0-9]{1}(?<!-s3alias|\.\..{1,63}|.{1,63}\.\.|\.\-.{1,63}|.{1,63}\.\-|\-\..{1,63}|.{1,63}\-\.)(?=$|\/)
I'm working on a college exercise and have the following question:
What is the domain of the "country" table?
My understanding of domain is that it defines the possible values of an attribute.
This means that the table "country" doesn't have a domain, but the various attributes in the table "country" have their own domains.
For example the attribute "SurfaceArea" has the domain FLOAT(10,2) and the attribute "Name" has the domain CHAR(52).
Is this correct?
http://en.wikipedia.org/wiki/Relational_database#Domain
Here is one source and yes, you are correct, domain describes the possible values of an attribute.
Your understanding of domains is correct but not complete. Typically, a domain is implemented as a data type like you specified. However, a domain can be more specific than the data type. Consider the attribute Grade, the possible values could be {A, B, C, D, F, I}. If you specify the data type as CHAR(1) then you are not eliminating invalid letters like G, H, J, etc. Consequently, it is important to understand what the original domain is and how it is different from the domain of the data type. Any remaining constraints such as eliminating those invalid values are typically implemented as an application constraints.A good reference on this is Elmasry and Navathe.
Obviously including spaces in table names, field names and control names is a bad idea (since it is used as a separator in practically all the imperative programming languages use commercially today*). You have to surround those controls and fields with [], etc. I'm trying to demonstrate another one of the problems with spaces to someone else.
I seem to recall that there is a situation that can arise where because a field name has a space in it (e.g., "Foo ID") and a control based on it is also called "Foo ID", that you can end accidentally referencing the underlying field instead of the control.
e.g., you update Foo ID from empty to "hello world" and then you need to check the value for null before the record is saved; something like "me.[Foo ID]" returns Null instead of "Hello World"
How can I duplicate this unexpected behaviour?
(* - Lisp, Prolog and and APL aren't imperative programming languages)
Since the control name can't have spaces in it when you reference it in code using the default controls property of the form (ie, Me.Foo_ID), the spaces are replaced with underscores. So in your example, Me.Foo_ID would refer to the control, but Me![Foo ID] would refer to the underlying field. (Even this statement appears incorrect on further consideration: Me![Foo ID] almost certainly refers to the control named "Foo ID".)
As David Fenton rightly points out, the control itself can be named with spaces. And it can be referenced in code with spaces when referenced as follows: Me.Controls("Foo ID") or Me![Foo ID] as those forms can properly handle spaces. But if you want to use the shorthand, you'll need to add the underscore: Me.Foo_ID.
In that case Me.Foo_ID would return "Hello World" before the record is saved (while the form is Dirty), but Me![Foo ID] would return Null.
EDIT: After some testing I have not been able to actually reproduce the odd behavior you are after (using several different combinations).
Thanks to David Fenton for setting me straight (please let me know if I'm still off somewhere).
What is the meaning of I $E(R%%,I%%)>1 ? and why using %%?
Actually, if you are talking about Standard MUMPS (not any particular implementation)
the R%% is illegal syntax. I have seen the non-standard use of % in extensions to MUMPS, such as EsiObjects or InterSystems Cache Object Script, but the use in the question above is actually nonsense in standard MUMPS.
There is no particular significance to %%. Its just part of the variable name and I still don't understand MUMPS community obsession with using % in variable names and making them more obscure.
so the statement means IF $EXTRACT(R%%,I%%)>1 i.e if the extracted value from the string R%% at position I%% is greater than 1, do some more obscure stuff.
$EXTRACT(string,from) extracts a
single character in the position
specified by from. The from value can
be an integer count from the beginning
of the string, an asterisk specifying
the last character of the string, or
an asterisk with a negative integer
specifying a count backwards from the
end of the string.
Link to documentation: http://docs.intersystems.com/cache20102/csp/docbook/DocBook.UI.Page.cls?KEY=RCOS_fextract
I have a set of objects that I read information out of that contain information that ends up becoming a MATLAB m file. One piece of information ends up being a function name in MATLAB. I need to remove all of the not-allowed characters from that string before writing the M file out to the filesystem. Can someone tell me what characters make up the set of allowed characters in a function name for MATLAB?
Legal names follow the pattern [A-Za-z][A-Za-z0-9_]*, i.e. an alphabetic character followed by zero or more alphanumeric-or-underscore characters, up to NAMELENGTHMAX characters.
Since MATLAB variable and function naming rules are the same, you might find genvarname useful. It sanitizes arbitrary strings into legal MATLAB names.
The short answer...
Any alphanumeric characters or underscores, as long as the name starts with a letter.
The longer answer...
The MATLAB documentation has a section "Working with M-Files" that discusses naming with a little more detail. Specifically, it points out the functions NAMELENGTHMAX (the maximum number of characters in the name that the OS will pay attention to), ISVARNAME (to check if the variable/function name is valid), and ISKEYWORD (to display restricted keywords).
Edited:
this may be more informative:
http://scv.bu.edu/documentation/tutorials/MATLAB/functions.html