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Regular expression that Must have at least one letter

I have a case where I am using a queue of regular expressions to filter out specific items in an Observer pattern. The filter will place the values in specific controls based on their values. However 1 of the controls pattern is that it can accept ANY ASCII Character. Let me list the filters in their order with the RegEx
Column Rule Regex
Receiving 7 DIGITS #"^[1-9]([0-9]{6}$)" --->Works
Count 2 digits, no leading 0 #"^[1-9]([0-9]{0,1})$" --->Works
Producer any ASCII char. #".*" --->too broad
MUST contain a letter
Is there a regular expression that will accept any set of ASCII characters, but 1 of them MUST be a letter (upper or lower case)?
#"^(?=.*[A-Za-z])$" -->Didn't work
examples that would need to go into expression
123 red
red
123 red123
red - 123
red

If you want to match the whole rang of ASCII chars you may use
#"^(?=[^A-Za-z]*[A-Za-z])[\x00-\x7F]*$"
If only printable chars are allowed use
#"^(?=[^A-Za-z]*[A-Za-z])[ -~]*$"
Note the (?=[^A-Za-z]*[A-Za-z]) positive lookahead is located right after ^, that is, it is only triggered at the start of a string. It requires an ASCII letter after any 0 or more chars other than an ASCII letter.
Your ^(?=.*[A-Za-z])$ pattern did not work because you wanted to match an empty string (^$) that contains (?=...) at least one ASCII letter ([A-Za-z]) after any 0+ chars other than newline (.*).

You could try [A-Za-z]+.
It matches when there is at least one letter. You want something more specific?

How about
^.*[a-zA-Z]+.*$ ?
Between start and end of line, accept any number of any characters, then at least one a-z/A-Z character, then again any number of any characters.

Simple phone number regex to match numbers, spaces, etc

I'm trying to modify a fairly basic regex pattern in C# that tests for phone numbers.
The patterns is -
[0-9]+(\.[0-9][0-9]?)?
I have two questions -
1) The existing expression does work (although it is fairly restrictive) but I can't quite understand how it works. Regexps for similar issues seem to look more like this one -
/^[0-9()]+$/
2) How could I extend this pattern to allow brackets, periods and a single space to separate numbers. I tried a few variations to include -
[0-9().+\s?](\.[0-9][0-9]?)?
Although i can't seem to create a valid pattern.
Any help would be much appreciated.
Thanks,

[0-9]+(\.[0-9][0-9]?)?
First of all, I recommend checking out either regexr.com or regex101.com, so you yourself get an understanding of how regex works. Both websites will give you a step-by-step explanation of what each symbol in the regex does.
Now, one of the main things you have to understand is that regex has special characters. This includes, among others, the following: []().-+*?\^$. So, if you want your regex to match a literal ., for example, you would have to escape it, since it's a special character. To do so, either use \. or [.]. Backslashes serve to escape other characters, while [] means "match any one of the characters in this set". Some special characters don't have a special meaning inside these brackets and don't require escaping.
Therefore, the regex above will match any combination of digits of length 1 or more, followed by an optional suffix (foobar)?, which has to be a dot, followed by one or two digits. In fact, this regex seems more like it's supposed to match decimal numbers with up to two digits behind the dot - not phone numbers.
/^[0-9()]+$/
What this does is pretty simple - match any combination of digits or round brackets that has the length 1 or greater.
[0-9().+\s?](\.[0-9][0-9]?)?
What you're matching here is:
one of: a digit, round bracket, dot, plus sign, whitespace or question mark; but exactly once only!
optionally followed by a dot and one or two digits
A suitable regex for your purpose could be:
(\+\d{2})?((\(0\)\d{2,3})|\d{2,3})?\d+
Enter this in one of the websites mentioned above to understand how it works. I modified it a little to also allow, for example +49 123 4567890.
Also, for simplicity, I didn't include spaces - so when using this regex, you have to remove all the spaces in your input first. In C#, that should be possible with yourString.Replace(" ", ""); (simply replacing all spaces with nothing = deleting spaces)

The + after the character set is a quantifier (meaning the preceeding character, character set or group is repeated) at least one, and unlimited number of times and it's greedy (matched the most possible).
Then [0-9().+\s]+ will match any character in set one or more times.

Regex match certain amount of character and allow space inbetween

I am currently working on a regex which needs to match exactly 8 digits. But sometimes it occurs that there are spaces or dots between those numbers. This is the regex that i am currently using.
([0-9\ ?.?]{7,16})
It works fine most of the time, but the problem I am having is that it sometimes matches number with a lot of spaces tailing it so you will get something like 1234/s/s/s/s (/s stands for space) Or sometimes it is only matching spaces.
What i want is a regex that always matches at least 8 digits and also allows spaces and dots without detecting less then 8 digits. I know it may be stupid question, but I couldn't find anything I need elswhere.

Your ([0-9\ ?.?]{7,16}) expression matches 7 to 16 occurrences of any character that is either a digit, or a space, or a ?, or .. Yes, the ? inside [...] is a literal ?, not a quantifier.
You need to use an expression that will match a digit ([0-9]) and then exactly 7 sequences of a space or period ([ .]) followed with 1 digit, and to make sure you are not matching the digits in 123.156.78.146 you may use special boundaries:
(?<!\d[ .]?)\d(?:[. ]?\d){7}(?![ .]?\d)
if the space or . can only be 0 to 1 in between digits; or - if the space/dot can appear 0 or more times,
(?<!\d[ .]*)\d(?:[. ]*\d){7}(?![ .]*\d)
See the regex demo
The (?<!\d[ .]*) is a negative lookbehind that will fail any match if it starts with a digit that is followed with .(s) or space(s), and the (?![ .]*\d) negative lookahead will fail the match if the 7 digits you need are followed with .(s) or space(s) and a digit.

To solve this, describe the problem to yourself. You want to match one digit followed by seven repetitions of space-or-dot followed by a digit. This leads to a regular expression like \d([ .]?\d){7}. To avoid collecting the seven captures add a :? after the (. To capture the whole string, enclose it in brackets. Adding both changes gives the expression (\d(:?[ .]?\d){7}). If more than one space or dot is allowed between the digits then change the ? to a *.
To get just the eight digits out of the string I suggest using the string captured above and replacing any spaces or dots with nothing.

Minimum Length Regular Expression

I'm trying to write a regular expression that will validate that user input is greater than X number of non-whitespace characters. I'm basically trying to filter out begining and ending whitespace while still ensuring that the input is greater than X characters; the characters can be anything, just not whitespace (space, tab, return, newline).
This the regex I've been using, but it doesn't work:
\s.{10}.*\s
I'm using C# 4.0 (Asp.net Regular Expression Validator) btw if that matters.

It may be easier to not use regex at all:
input.Where(c => !char.IsWhiteSpace(c)).Count() > 10
If whitespace shouldn't count in the middle, then this will work:
(\s*(\S)\s*){10,}
If you don't care about whitespace in between non-whitespace characters, the other answers have that scenario covered.

This regular expression looks for eight or more characters between the first and last non-whitespace characters, ignoring leading and trailing whitespace:
\s*\S.{8,}\S\s*

If your trying to check (like in my case a phone number that contains 8 digits) , you need to refer to a number below the one you need.
(\s*(\S)\s*){7,}

Regular expression - match character, digits and special characters

I have the following string:
test123 test ödo 123teö"st 123 m.1212 123t.est
I only want to match strings as a whole that have either characters, digits and special character mixed together. So the regex should match the following string of the example above:
test123 test ödo 123teö"st 123 m.1212 123t.est
Could someone help me out please?
Update
Sorry for not giving a clear explanation of what I need.
I am using C#.
I need to find words that contain alphanumeric strings (eg abc123, 123abc, a1b2c3, 1abc23 etc). Also I need to find strings that contain any kind of symbols (symbols = anythings else than word characters and digits) (eg abc"123, "abc, ab?dd, 100mm", 345t{asd]dd)
If I find a match, I need to "tokenize" (separate digits, word characters and symbols with whitespace) these strings so abc123 becomes abc 123 or 345t{asd]dd becomes 345 t { asd ] dd etc

Assuming you're using a regex flavor that supports lookaheads and Unicode properties, this should get you started:
(?!(?:\pL+|\pN+|\pP+)(?!\S))\S+
\S+ matches one or more non-whitespace characters, but only after the negative lookahead asserts that those characters are not all letters (\pL), digits (\pN), or punctuation (\pP). The inner negative lookahead--(?!\S)--ensures that the outer one examines all the characters in the word.
Although it might satisfy your requirements, this regex is really just a demonstration of the technique you'll probably want to use. As it is, it can be fooled by "words" with (for example) control characters or dingbats in them.

The answer to the question you’ve actually asked is (?s).+, but perhaps you would care to refine your question.